feedbacks, runaway, and tipping points

There’s been some discussion on Twitter about feedbacks, runaways, and tipping points. The issue is that some seem to confuse these and sometimes imply that we could cross thresholds where we’ll undergo a runaway. I thought I would briefly try to explain these terms.

In the context of climate change, external factors that can lead to warming are typically called forcings. This would be things like changes to the solar flux, volcanic eruptions, and our release of greenhouse gases into the atmosphere. Feedbacks are then responses to this externally driven warming that either act to amplify, or suppress, the warming. Some of these are fast, such as water vapour and clouds, while others are slower, such as changes to vegetation or ice sheets. Some are also negative and quite strong (such as the Planck response). This means that even though the overall effect of these feedbacks is to amplify the externally-driven warming, it is limited (the negative feedbacks eventually balance the the effect of the change in forcing and the resulting positive feedbacks). For example, if we were to double atmospheric CO2, we’d expect to eventually warm by about 3oC.

A runaway, on the other hand, typically refers to what happened on Venus. Essentially, virtually all of the CO2 was released into the atmosphere, the warming was so substantial that any liquid water evaporated and was eventually lost to space, most atmopsheric molecules lighter than CO2 were also lost to space, and the surface warmed by many 100s of oC. On the Earth, such a runaway is simply not possible, because most of the carbon, that can then form CO2, is locked up in the lithosphere. We can’t emit enough CO2, either through anthropogenic influences or naturally, to undergo a runaway.

Finally, a tipping point refers to us crossing some threshold where the climate system changes (tips), irreversibly, into a new state. There is the possibility of a global tipping point, but this is seen as very unlikely. However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice.

If we were to cross any of these tipping threshold, then the changes would further amplify the warming (through either releasing additional CO2, or methane, or changing the albedo) and – in the case of the ice sheets – would lead to substantial sea level rise. There are a few things to bear in mind, though. The timescales are typically long; if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie; we could already have crossed some, or might not do so unless we were to warm substantially. Additionally, there is still debate as to whether or not some of these are truly irreversible; if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse?

So, one does have to be slightly careful as to what one implies about tipping points and their significance. On that note, I was going to highlight a recent paper by James Annan that might initiate an interesting discussion about using tipping points in the public narrative. However, this has got long enough, so I will leave that to another post.

Update: Something I meant to stress, is that even though crossing some tipping point might lead to irreversible changes that would amplify our warming, it is still limited. There is only so much that these effects can change the albedo, and there is a limit to how much CO2, or methane, that they could release.

Update 2: If you want to read a more detailed description of the runaway greenhouse effect there is a very good Skeptical Science post by Chris Colose. There is a formal aspect to a runaway that I hadn’t appreciated, but was made aware of by MarkR’s comment. It involves a condensable greenhouse gas (such as water vapour) in equilibrium with a surface reservoir, accumulating in the atmosphere so that it eventually limits the outgoing longwavelength flux. If the incoming flux exceeds this, then energy will accumulate without there being any way to balance this. The surface will then undergo runaway warming until the entire surface reservoir of the condensable greenhouse gas has been depleted.

For water vapour, this longwavelength limit would occur at about 310W/m^2, which – given our albedo of 0.3 – is currently greater than the flux we’re receiving from the Sun. This essentially means that water vapour in the atmosphere is in a regime where it condenses, rather than accumulates. We, therefore, can’t undergo such a runaway in our current state, and no level of CO2 emissions will trigger it.

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208 Responses to feedbacks, runaway, and tipping points

  1. dikranmarsupial says:

    Thank heavens for T^4 ;o)

  2. The Planck response, for those who don’t know 🙂

  3. John Hartz says:

    There has also been a lot of articles and opinion pieces published on these issues over the past months. I will post links to some of them in subsequent comments. I do, however, want to draw your attention to a recent analysis by David Roberts about a “tipping point” in a societal context…

    Social tipping points are the only hope for the climate by David Roberts, Energy & Environment, Vox, Jan 29, 2020

  4. Social tipping points are a slightly different issue (although similarly defined as sudden changes to our societies), but I think they’re more of a worry than climate tipping points. I wrote a post about this a while ago.

  5. From the condensed matter world, there’s a straightforward approach to finding the set-points of a catalyzed positive feedback system. In the climate case, the catalyst is CO2 and the main species is H20. I tweeted this a few days ago:

  6. MarkR says:

    I think we *can* do a runaway greenhouse on Earth, I understood that the “standard” runaway model just needs a GHG with sufficiently broad absorption bands that responds to temperature, like H2O:
    https://en.m.wikipedia.org/wiki/Komabayashi-Ingersoll_limit
    We get enough sunlight to do this but so long as we have enough bright clouds we’ll be ok…

    Did I misunderstand this or were you referring specifically to a Venus-like CO2 greenhouse?

  7. Greg Robie says:

    Unless I misunderstood, the loss of the planet’s cryosphere is not calculated into the #SR15 assertion regarding no committed warming at zero carbon emissions. Concerning that 3°C temperature rise, the Arctic is already there … and it’s cryosphere is collapsing. The non-polar cryosphere is collapsing. The Antarctic cryosphere looks increasingly like it is tipped.

    To call these slow feedbacks is a bit anthropocentric.

    Furthermore, seasonal dynamics regarding the cryosphere are both poorly understood and poorly modeled. Aren’t averages yet an as-good-it-gets … that are significantly not-good-enough (but for motivated reasoning)? For example, all of January has been this winter’s maple sugaring season in the mid-Hudson Valley. The red and silver maples are budding and this next week of warmth will end the sugaring season about the time it usually starts. We have not had winter. There is no snow cover nor frost in the ground. Ice out is underway. Usually (again) the frost is still going into the ground – even with an insulating snow cover. This means that a seasonal reserve of cold (latent heat of ice) will be absent in our normal spring. Air masses will warm much quicker and sooner. 90% of this additional heat will go into the oceans … the great puddle where [significant?] errors/oversights go to drown?!?

    And let us be slow to forget that the models and metrics that yielded that touted 3°C number are shifting higher. Imagine a number that wasn’t based on a one model one vote ‘standard’ … or what that 3°C number is when such is the result of a bit more scientific rigor?

    On the forcing side, this post continues to ignore increased refraction due to a warming troposphere. Particularly as such relates to twilight dynamics. And particularly the Arctic since I last commented about this Inuit observation here, I thought of another metric to consider. Due to our oblate spheroid and troposphere differences between than n this tipping pointe pole and the equator

    sNAILmALEnotHAIL …but pace’n myself

    https://m.youtube.com/channel/UCeDkezgoyyZAlN7nW1tlfeA

    life is for learning so all my failures must mean that I’m wicked smart

    >

  8. Greg Robie says:

    That one got away too soon. I’ve yet to learn not to use this new-to-me iPhone 6 while it is charging. When plugged in the screen develops a mind of its own!

    sNAILmALEnotHAIL …but pace’n myself

    https://m.youtube.com/channel/UCeDkezgoyyZAlN7nW1tlfeA

    life is for learning so all my failures must mean that I’m wicked smart

    >

  9. Mark,
    I was referring to a Venus-like runaway. If I understand what you’re referring to, we’d essentially have to get to an albedo of close to 0.95 [Edit: other way around – an albedo smaller than 0.05, not 0.95] for that effect to manifest. I guess we can’t rule it out, but – as you say – if we have enough bright clouds, we should be okay.

  10. I just found this Skeptical Science post, by Chris Colose, that explains the runaway greenhouse effect very nicely.

  11. David B. Benson says:

    aTTP, title reads “feebacks”.

  12. Yes, we are not going to runaway to Venus conditions. And many tipping points and feedbacks will take decades or centuries to really be felt, so maybe there is really no reason to worry about the warming. We should all be okay. It is certainly a shame when people are careless about how they discuss their concerns with global warming. Thanks for this post.
    Cheers
    Mike

  13. Jon Kirwan says:

    Just FYI, but I can’t recall reading a better book on the topic (as mathematics and NOT as climate) of runaway, tipping points, etc., than Bob Gilmore’s “Catastrophe Theory for Scientists and Engineers.” I really enjoyed it and gave me a rich set of thinking tools (in my opinion, of course.) To those who haven’t read it, they have my recommendation. (I also enjoyed his “Lie Groups and Algebras” book.)

  14. David B. Benson says:

    smallbluemike, there are already plenty of “not alright”. For example, the West Coast shellfish industry is being impacted by the change in seawater pH.

  15. At DBB: maybe you are right about the shellfish, but I did not pick up on immediate ecosystem concerns from reading this post. The point seemed to be a concern about the language we use to describe the things we are seeing. Like ATTP said, “if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie…” How will we know for sure if the impact from seawater pH is a serious problem or has passed a threshold? How can we be sure that the changes are not reversible or that new negative feedbacks won’t arise that will slow the changes even more? We don’t a lot of evidence that the oceans are on their way to a P-T extinction event or Canfield status. That would probably take thousands of years to develop.

    I think in this instance, with seawater changes, we are talking about a simple forcing – that increased CO2 in the atmosphere leads to changes in seawater pH. There probably is no feedback or tipping point or runaway process, it is just a forcing that will proceed over an extended period of time. I think we are being encouraged to discuss these things carefully and avoid getting carried away. The shellfish issue is a simple forcing, is it not? Isn’t that what this post is about?

  16. David B. Benson says:

    smallbluemike — The ocean surface water pH is directly linked to the atmospheric concentration of carbon dioxide. “Just” lower the concentration and that problem solves itself. But there is the deep ocean pH, with a time scale of centuries.

  17. izen says:

    There can be quite profound and relatively rapid regional, or local, tipping point changes from a shift in climate. The two most obvious in the transition from the last glacial period to the current interstadial ~7000 years ago are the flooding of Doggerland and the desertification of the Sahara.

  18. If, given a time series, someone could say how to calculate its “tipping point,” that would be a good thing.

  19. David B. Benson says:

    A permanent change to the landscape, so a regional “tipping point”:
    https://en.m.wikipedia.org/wiki/Missoula_Floods
    No going back from this; a permanent change.

  20. Ben McMillan says:

    ‘Tipping points’ are associated with hysteresis: turn the control knob up from 0 to 11, and the system suddenly flicks to another state. Turn the control down from 11 to 0, and it stays there:
    https://en.wikipedia.org/wiki/Hysteresis#/media/File:StonerWohlfarthMainLoop.svg

    So if you are just looking at the output time series, then it is hard to know whether you have a tipping point. You see one or more sharp transitions (smoothed step function/square wave) in the output when the input is varied smoothly, but that isn’t a smoking gun by itself. A better way to identify it by drawing curves of input versus output.

    Also, most of these tipping points are bad things that you don’t want happening: if you are identifying it in the time series, the bad thing has already happened.

  21. Tony McLeod says:

    Tipping points are time dependant. A slow change may not trigger a tipping point a fast change does. One of the denier talking points is “it was at 1000ppm back when and nothing bad happened…in fact it was better”, but historically CO2 concentration changes have taken tens of millennia or more usually millions of years to unfold.
    The rapidity of the temperature rise is the problem and changes to the physical world are going to be trivial compared the biological. It is highly likely we have already triggered an unfathomable number of biological tipping points – mostly in the demise of species that simply can’t migrate fast enough or at all, or could have but now there is a city or a million hectares of wheat in the way.
    Large, slow-breeding mammals can easily migrate away from gradually rising seas but they rarely do well in a rapid, cascading extinction.

  22. Dave_Geologist says:

    izen, IIRC is has been suggested that the last straw for Doggerland was inundation by the tsunami caused by the Storegga Slide, off Norway. Obviously the water drained away, but erosion and the damage to natural coastal defences, and the killing of soil-binding vegetation by seawater, made it vulnerable to winter storms. And of course anyone who was living there drowned. Eastern Scotland, on the sidewall of the tsunami and just north of Doggerland, was flooded up to 80 km (50 mi) inland and 4 m (13 ft) above current normal tide levels. The shape of the North Sea would have focused even more water onto Doggerland, which was much lower lying and a dead end.

    The trigger for the slide is still debated: earthquake on the Møre-Trøndelag Fault related to post-glacial unloading, or destabilisation of clathrates related to post-glacial warming. Or both: the original earthquake-induced slide stripped off enough cover to decompress and destabilise the clathrates, and the seabed boiled causing more collapse.

    Just as well we’re not currently in a warming world with coastal earthquakes ongoing and clathrates on some of those continental margins. Err…

  23. In regards to clathrates as a possible tipping point, a more thorough discussion of activation energies a la heat of vaporization needs to be pursued. The liquid or ice to water vapor activation energy is well known and this determines the positive feedback that will occur with CO2 as a catalyst. If the activation energy of clathrates to form methane is higher than H20 heat of vaporization, then it may be that this creates a stronger positive feedback, but if the activation energy is low it may kick in earlier but not be as strong a function of temperature. This is all a function of the specific property of Arrhenius rate laws ~ exp(-E/kT).

    As an example from the world of Silicon Valley, silicon has a heat of vaporization of 384 kJ/mol but it takes temperatures of 900C to start outgassing at a measurable rate. On the other hand, solid arsenic used to create gallum arsenide devices has a heat of vaporization of only 35 kJ/mol and it will start measurably outgassing at 300C. In a vacuum environment, solid pure arsenic will sublimate completely without ever turning into a liquid! (I’m not sure what it does on heating to that temperature in air, other than being dangerous)

    So I am curious about the properties of methane clathrates or methane hydrates, starting from some of these fundamental properties of heat of vaporization and heat of sublimation, and what factor that overlying pressure has on the phase plot. Googling around a bit and I’ve found nothing definitive yet. Will have to ask Eli Rabbett about what he thinks.

  24. Not-in-my-name says:

    There was physics before this nonsense started. This article shows that understanding of the fundamentals of thermodynamics is beyond the capability of most people. The terms “feedback”, “runaway” and “tipping points” have no meaning in thermodynamics and will never be found in any text book on the subject. The only tipping point in this is the stupidity of the human race.

    It starts with the use of the term “forcing” to describe an external factor that can cause warming. This is a ridiculous concept when it is the sun that is creating all the climate on earth and more importantly is essential to all life on earth. It shows how climate scientists reduce the sun to something that seems unimportant. They have to do this because they could not create the ludicrous concept of humans being responsible for warming the earth and causing the climate to change. The concept is nonsense considering what we know about the past climate change on earth. The description suggests that without these factors we would still have a climate and could survive.

    There are no feedbacks in thermodynamics that can “amplify or supress warming”. How science can sink to the level of this belief is beyond my comprehension. We have a fundamental law of physics – the conservation of energy – which clearly makes the concept of feedbacks impossible because it would mean that energy could be created from nothing and be destroyed. We have another law – conservation of matter. Einstein brought these together with his famous E=mC2 equation. If there is amplification or suppression of energy then Einstein is wrong.

    There is no runaway in thermodynamics because all heat transfers tend to an equilibrium. There is no runaway on Venus. The high temperature is entirely due to the huge mass of the atmosphere and the well know gas law. When a gas is compressed the temperature increases. Gravity and the mass of the atmosphere is the cause of the temperature on Venus. The atmosphere is so dense that the sun’s radiation cannot penetrate to the surface. Mars also has an atmosphere mainly of carbon dioxide but it does not have high temperatures for the simple reason that it is not a dense atmosphere. The gas law also increases the temperature on the surface of the earth and not the invented greenhouse effect.

    It is quite obvious from the past climate history that there have not been any irreversible tipping points. The earth’s climate history has been one of cooling since it was created. My view is that it has been stable for at least 500,000 years through the ice ages. The climate does not exist for us and we cannot control it. All live evolved because of the climate and humans only evolved recently because the present climate and the warming climate of the last 20,000 years was vital to our success. The danger to humans is cooling. The nonsense in this article is entire because thermodynamics has been reduced to considering temperature when it should be about energy. I suggest that you plot the proxy average global temperatures for the last 500,000 years in degrees Kelvin with 0K as the axis. All you will see is a flat line. We evolved and are successful because we adapted to the climate and we have absolutely no control over it. In order to survive will we have to continue to adapt but we now seem too stupid to realise that.

  25. Dave_Geologist says:

    Paul

    Natural Gas Hydrates, Sara E. Harrison, October 24, 2010

    Clathrate hydrates

    Pretty sure I’ve seen footage of them degassing spontaneously on the deck of a ship. And when they’re lit, it’s the gas coming out that burns not the solid. The gas is not chemically bonded with the water molecules, just sitting in holes or cages in the ice structure with only weak van der Waals forces between them. So I’d expect a very small activation energy for degassing. Although if the permeability of the clathrate is very low the limiting factor might be diffusion of the gas out of the lattice. So maybe we should be thinking about melting and a latent heat of fusion for rapid, large-scale release.

    I’d be more worried about tundra because there you have scope for a large area at more-or-less the same elevation and temperature warming past the critical threshold at round about the same time. As is envisaged for the Antarctic plateau in some models for the PETM. Slow degassing as the thaw expands uphill, adding a small area each year, then the whole plateau goes at once.

    Subsea you need to be in a place where the hydrothermal gradient and phase boundary intersect just above the seabed. Methane hydrates usually occur on continental slopes (the shelf-edge typically being around 200m), so any degassing would be piecemeal, progressing from shallow to deep.

  26. Not-in-my-name,

    The terms “feedback”, “runaway” and “tipping points” have no meaning in thermodynamics and will never be found in any text book on the subject.

    So what? This isn’t about thermodynamics, this is about what this terminology means in the cimate context. The whole point of this post is to explain what these terms mean in this context. Just because they don’t have a similar meaning in thermodynamics doesn’t suddenly challenge this.

    It starts with the use of the term “forcing” to describe an external factor that can cause warming. This is a ridiculous concept when it is the sun that is creating all the climate on earth and more importantly is essential to all life on earth. It shows how climate scientists reduce the sun to something that seems unimportant.

    No, they don’t reduce the Sun to something that is unimportant. Everyone involved knows that the energy almost all comes from the Sun (barring a small amount of geothermal). The Sun, however, doesn’t vary very much, and so most of the changes that we experience are due to other external factors (orbital variations, volcanoes, greenhouse gas emissions).

    There are no feedbacks in thermodynamics that can “amplify or supress warming”.

    Again, so what? Feedback in this context have units of W/m^2/K, so either amplify, or suppress, the externally driven warming/cooling.

    It is quite obvious from the past climate history that there have not been any irreversible tipping points.

    In this context “irreversible” means it won’t change back for a very long time (irreversible on human timescales), not that it will never ever change back. There have clearly been past changes that qualify as tipping points as defined in this context.

    I suggest that you plot the proxy average global temperatures for the last 500,000 years in degrees Kelvin with 0K as the axis. All you will see is a flat line.

    Yes, of course you will, but so what? Our current species hasn’t even been around for 500000 years and most of our advances happened during the Holocene, when temperatures were remarkably stable. We’re currently pushing them well outside this range, which has the potential to be severely disruptive. If all you care about is whether or not we will still be here in a few hundreds years time and think we will find some way to adapt to the changes, then we’ll probably be fine. My preference is to try and get there in a way that isn’t highly disruptive and that doesn’t lead to substantial suffering.

  27. Chubbs says:

    Building on TonyM’s comment, the distance from our recent stable climate is a key metric. The amount of warming determines how far our various climate systems are from equilibrium. Kind of like pulling on a rubber band. At some point it is stretched too far.

  28. Dave_Geologist says:

    ATTP, re Venus: what do you think of these papers (if I’m permitted to be a bit exoplanet-OT 😉 )? The first, Increased insolation threshold for runaway greenhouse processes on Earth-like planets, suggests that, at least for an Earthlike world, a “cold trap” exists at the top of the troposphere where water vapour freezes out. That keeps the stratosphere dry, so the planet can’t lose water to space and carries on heating until the oceans have boiled and the surface becomes red-hot and finds a gap in the water vapour absorption spectrum. Do we know Venus can’t have followed that path (too dry today? does that mean it must have had a lower initial water inventory? if Earth’s water was delivered during the late Heavy Bombardment, how would it differ on impact with a red-hot planet?).

    I see that there’s a Pierrehumbert paper Water loss from terrestrial planets with CO2-rich atmospheres out around the same time which I’ve not yet read properly (it’s heavy going 😦 ) which perhaps answers my question (Fig. 10). The first paper focused on planets near the insolation threshold for a runaway greenhouse. Further in, I presume insolation could be high enough that the surface temperature keeps the upper troposphere above freezing and allows a moist-stratosphere runaway, with stratospheric water gradually stripped away. Although I do see a couple of papers referenced which say Venus was drier anyway and lost its water during planetary solidification (again, due to being closer in?). That I would think is consistent with this paper, Emergence of two types of terrestrial planet on solidification of magma ocean, where Venus would be a Type II planet which had a water atmosphere and a runaway greenhouse while it still had a magma ocean (or perhaps it cooled then was warmed again to red-hot by the runaway greenhouse, or the LHB which the second paper touched on?).

    Coming back OT, I found this paper to be a very good explanation for the non-specialist of runaway greenhouse conditions and the constraints on what Earth can and can’t undergo. The runaway greenhouse: implications for future climate change, geoengineering and planetary atmospheres. It agrees that Earth can’t be driven into a Venus-like runaway greenhouse by CO2 alone; it would require increased insolation. It does suggest however that Earth could be driven into a moist greenhouse by CO2 alone, with no runaway but with the cold trap removed and a moist stratosphere from which water would be stripped away over time (a longer timeframe than we care about). Since we might also be looking at 40-50°C warming by then and the loss of the ozone layer, we’d probably be past caring anyway 😦 .

  29. Dave,
    I think that’s all related to the second update I added at the end of the post. For a true runaway, you need to get to the point where the water vapour has limited the outgoing flux and the incoming flux exceeds this level (so that energy continually accrues within the climate system). It’s interesting that the first paper suggests that this is at an even higher level than has been thought (around 375W/m^2, rather than at around 310W/m^2).

    As you highlight at the end, even if a runaway isn’t possible, we could end up in a moist greenhouse phase with water vapour up in the stratosphere. However, I think this is also regarded as unlikely.

  30. izen says:

    @-NIMN
    ” The gas law also increases the temperature on the surface of the earth and not the invented greenhouse effect.”

    But when there is a high pressure weather front it gets colder, and when it is low pressure the weather gets warmer.
    The ugly observations appear to contradict your ‘beautiful theory’.

  31. Dave_Geologist says:

    Yes ATTP, by half-way through I realised I was answering my own question. The inner edge of the Goldilocks Zone comes spookily close to Earth’s orbit, although of course it was much further in for most of the time life was evolving. The high-pCO2, hot-water worlds (hotter than 100°C) were a new concept to me. It should have been obvious though: the most temperature-tolerant Earth life lives around hydrothermal vents at more than 100°C because they’re in the deep ocean. A deep, dense atmosphere can do the same.

    It’s also interesting that although the 1D models were a good guide, the full 3D model revealed some wrinkles and refinements. For example the Hadley cells mean that some parcels of atmosphere are never water-saturated, even if most it is. And the behaviour of clouds is a big deal, and whether they’re a positive or a negative feedback (plus ça change…). You could see it as another sort of tipping point. Instead of a positive forcing suddenly being increased, e.g. by CH4 emission, and perhaps driving more forcing through positive feedback, you have a negative (Planck) feedback stopping dead at a fixed value. Or perhaps it should be seen more as a bifurcation point, like a completely ice-free Earth or a Snowball Earth, where one of the feedbacks either ceases to exist or hits an upper limit. My picture of the runaway greenhouse had been somewhat different, until I read the final paper which is why I recommended it. It’s also open access.

  32. dikranmarsupial says:

    “I suggest that you plot the proxy average global temperatures for the last 500,000 years in degrees Kelvin with 0K as the axis. All you will see is a flat line.”

    Sadly the diagrams from DenialDepot’s article on “how to cook up a graph” are now missing. I think someone doesn’t realise it was a parod you, rather than a tutorial! ;o)

  33. Dave_Geologist says:

    If we plot the Earth’s orbit around the Sun on a graph with the origin at Alpha Centauri, the locations of the Earth and Sun are indistinguishable and no orbit is visible. Therefore Copernicus was wrong and the Earth doesn’t orbit the Sun.

  34. John Hartz says:

    I suspect that the total disintegration of the Thwaites glacier would be considered a tipping point. Here’s the latest research findings about what’s happening to it as we chit chat..

    Scientists have found warm water beneath Antarctica’s “doomsday glacier,” a nickname used because it is one of Antarctica’s fastest melting glaciers. While researchers have observed the recession of the Thwaites Glacier for a decade, this marks the first time they detected the presence of warm water – found at a “vital point” beneath the glacier.

    A news release on the findings called it an alarming discovery.

    “The fact that such warm water was just now recorded by our team along a section of Thwaites grounding zone where we have known the glacier is melting suggests that it may be undergoing an unstoppable retreat that has huge implications for global sea-level rise,” David Holland, director of New York University’s Environmental Fluid Dynamics Laboratory and NYU Abu Dhabi’s Center for Global Sea Level Change, which conducted the research, said in the news release.

    Scientists alarmed to discover warm water at “vital point” beneath Antarctica’s “doomsday glacier” by Sophie Lewis, CBS News, Feb 1, 2020

  35. Willard says:

    Speaking of the Sun:

  36. is there really such a thing as a true runaway state? Is Venus continuing to get hotter?

    Isn’t this idea of a runaway, just a transition in temp states that happens until some sort of new equilibrium develops?

    On those lines, when people talk about runaway warming, I normally think of a change in the carbon cycle of the planet that will raise global temp unexpectedly in a significant amount. That significant amount might only be a degree or two, or maybe 3 or 5. In any instance where the global temp suddenly* jumped by more than a degree, our civilizations and ecosystems would be quite stressed.

    Suddenly means anything under a century in this instance. I don’t know if this could happen in a time frame of a decade or two. I assume there is a lot of temperature inertia in this large system.

    I do think it is fascinating to watch our species test the boundaries and stability of global climate. We have launched the largest science experiment of our species’ history with the CO2 emissions of the past three decades. I don’t think that is hyperbole. As we can see from NIMN, not everyone is convinced yet that the greenhouse hypothesis has been proven. We are a species that loves a science experiment!

    Go Team!

    Mike

  37. at JH regarding the tipping point of the doomsday glacier. I think ATTP alluded to this kind of thing when he said

    “There is the possibility of a global tipping point, but this is seen as very unlikely. However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice.

    If we were to cross any of these tipping threshold, then the changes would further amplify the warming (through either releasing additional CO2, or methane, or changing the albedo) and – in the case of the ice sheets – would lead to substantial sea level rise. There are a few things to bear in mind, though. The timescales are typically long; if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie; we could already have crossed some, or might not do so unless we were to warm substantially. Additionally, there is still debate as to whether or not some of these are truly irreversible; if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ”

    The melting of the Thwaite glacier will take the typical long time that is described above, if the melt is happening in a manner that we would recognize as a tipping point. Once we are certain that this change state is happening and it is a tipping point and not a simple forcing, we should be able to study and determine the speed of the melt and then we will have a time frame that we can work with to study whether this melt is reversible.

    I think ATTP has addressed this kind of potential tipping point in a very sensible manner: “one does have to be slightly careful as to what one implies about tipping points and their significance.”

    Doomsday glacier seems less than careful in this context. I look forward to reading a post on James Annan’s paper on discussion of tipping points in public discourse.

    Cheers

    Mike

  38. John Hartz says:

    Bob Berwyn asserts that an ecological tipping point has already been reached…

    As extreme wildfires burn across large swaths of Australia, scientists say we’re witnessing how global warming can push forest ecosystems past a point of no return.

    Some of those forests won’t recover in today’s warmer climate, scientists say. They expect the same in other regions scarred by flames in recent years; in semi-arid areas like parts of the American West, the Mediterranean Basin and Australia, some post-fire forest landscapes will shift to brush or grassland.

    More than 17 million acres have burned in Australia over the last three months amid record heat that has dried vegetation and pulled moisture from the land. Hundreds of millions of animals, including a large number of koalas, are believed to have perished in the infernos. The survivors will face drastically changed habitats. Water flows and vegetation will change, and carbon emissions will rise as burning trees release carbon and fewer living trees are left to pull CO2 out of the air and store it.

    In many ways, it’s the definition of a tipping point, as ecosystems transform from one type into another.

    In Australia’s Burning Forests, Signs We’ve Passed a Global Warming Tipping Point by Bob Berwyn, InsideClimate News, Jan 8, 2020

    FWIW, Berwyn’s assertion resonates with me.

  39. John Hartz says:

    smallbluemike: I stated in my initial comment on this thread,,,

    There has also been a lot of articles and opinion pieces published on these issues over the past months. I will post links to some of them in subsequent comments.

    I believe it behooves us to compare how scientists such as ATTP employ “tipping point” terminology to how science journalists use the term in MSM media. I suspect many more people read MSM articles than read ATTP’s OPs.

    If we conclude that a climate journalist is using the term “tipping point” in grossly inappropriate way, then we should communicate our concerns directly to that journalist.

  40. well done, JH. by citing the Australian fires as a potential tipping point, you may identified a fast tipping point. I read a piece somewhere recently that talked about some of the feedbacks/tipping points by referring to them as zombies. That discussion reflected on the fact that we have been assuming that all zombies move slowly. Then, as film history indicates, the fast-moving zombie appears and we are all off to the races!

    Australian fires as a tipping point do seem quite fast when compared to glaciers melting! Impressive and cinematic, but I think ATTP is correct: one does need to be careful when discussing these matters, clearly most of them will take a long time to manifest and be proven as tipping points.

    I think the zombie reference is like the doomsday glacier framing, it is not careful. I think it may be sensible to cancel vacation plans to Australia now and give this a little time to get sorted. If you were planning to snorkel at the Great Barrier Reef this year, maybe that opportunity has slipped away? Take the vacation to Ecuador instead and enjoy the Galapagos Islands. Count tortoises! Quite slow moving and in population recovery thanks to Diego.

  41. running through MarkR’s comments leads to this definition for runaway greenhouse effect:

    A runaway greenhouse effect is when there is enough of a greenhouse gas in a planet’s atmosphere such that the gas blocks thermal radiation from the planet, preventing the planet from cooling and from having liquid water on its surface. The runaway greenhouse effect can be defined by a limit on a planet’s outgoing longwave radiation which is asymptotically reached due to higher surface temperatures boiling a condensable species (often water vapor) into the atmosphere, increasing its optical depth.[1] This runaway positive feedback means the planet cannot cool down through longwave radiation (via the Stefan–Boltzmann law) and continues to heat up until it can radiate outside of the absorption bands[2] of the condensable species.

    The runaway greenhouse effect is often formulated with water vapor as the condensable species. In this case the water vapor reaches the stratosphere and escapes into space via hydrodynamic escape, resulting in a desiccated planet.[3] An example of this is believed to have happened in the early history of Venus.

    https://en.m.wikipedia.org/wiki/Runaway_greenhouse_effect

    It is helpful to spell out the definitions. When the greenhouse effect strips away all liquid water from the planet surface, that is runaway warming. A useful definition for runaway to have in hand. I don’t think we are ever going to see that on Earth.

  42. Dave_Geologist says:

    Mike, I would call that a tipping point. Otherwise we’d need a new word for runaways 😉 . There is a limited store of whatever it is we’ve released, and once it’s exhausted we go back to BAU. And it’s a forcing, not a feedback. The same feedbacks that were there before are still operating.

    I would use a runaway for situations in which the net feedback (including Planck) is greater than +1. Or, as per Fig. 1 of the last reference I gave, climate sensitivity is infinite. Even if the forcing stays the same, we just keep on warming “for ever”. I suppose there you also have a situation where the reservoir becomes exhausted or the rules change, so it’s not really “for ever”. But it’s a very long time: millions or billions of years. In the moist-stratosphere case, either you run out of water through photo-dissociation and hydrogen escape to space, or the surface becomes red hot and radiates directly to space at wavelengths where water vapour is transparent. In the dry-stratosphere case, you can’t lose water and have to wait for the rule-change when the surface becomes red-hot.

    The Earth’s current (albedo-adjusted) flux is the star in Fig. 5. If you add CO2 we move to the right but stay below the blue line at about 290 W/m² (probably not a dead flat line because of secondary factors). So we can’t reach the tropospheric asymptotic limit of Fig. 1 (the dry-stratosphere runaway). But if we make the Sun hotter at current CO2 levels, we follow path 2, and enter a runaway at the hump (we emit less radiation as we get hotter, even if we hold insolation constant, and get hotter faster). The analogy with a Snowball Earth is that past the threshold ice cover (about when it reaches the tropics) you are also in a runaway situation with feedback greater than +1. Every square mile of ice you add increases the albedo enough to freeze more than one square mile of sea.

  43. Dave_Geologist says:

    ATTP, is the 375 W/m² vs. 310 W/m² to do with whether it’s a moist-stratosphere runaway or a dry-stratosphere runaway? They look suspiciously close to the c. 380 W/m² and c. 290 W/m² lines in Fig. 1 of my final reference.

  44. Greg Robie says:

    Again, & finished on a charged device…

    Unless I misunderstood, the loss of the planet’s cryosphere is not calculated into the #SR15 assertion regarding no committed warming at zero carbon emissions. Concerning that 3°C temperature rise, the Arctic is already there … and it’s cryosphere is collapsing. The non-polar cryosphere is collapsing. The Antarctic cryosphere looks increasingly like it is tipped.

    To call these slow feedbacks is a bit anthropocentric.

    Furthermore, seasonal dynamics regarding the cryosphere are both poorly understood and poorly modeled. Aren’t averages yet an as-good-it-gets … that are significantly not-good-enough (but for motivated reasoning)? For example, all of January has been this winter’s maple sugaring season here in the mid-Hudson Valley. The red and silver maples are budding and this next week of warmth will end the sugaring season about the time it usually starts. We have not had winter. There is no snow cover nor frost in the ground. Ice out is underway.

    Again, ‘usually’ the frost is still going into the ground – even with an insulating snow cover. This is when really cold Arctic air masses make it this far south. Given the Gulf Stream you UK lads might not think too much about this. Anyway, this means that a seasonal reserve of cold (latent heat of ice) that winter normally stores around here will be missing in action in our normal spring. Air masses will warm much quicker and sooner. 90% of this additional heat will go into the oceans … the great puddle where [significant?] errors/oversights go to drown?!?

    And let us be slow to forget that the models and metrics that yielded that touted 3°C number are shifting higher. Imagine a number that wasn’t based on a one model one vote ‘standard’ … or what that 3°C number is when such is the result of a bit more scientific rigor?

    On the forcing side, this post (& science, in general) continues to ignore increased refraction due to a warming troposphere. Particularly as such relates to twilight dynamics. And particularly in the Arctic. Since I last commented about the Inuit observations regarding increased refraction here, I’ve thought of another metric to consider … or to continue to ignore. Due to our home’s oblate spheroid shape and troposphere differences between pole and the equator (due to thermal expansion and centrifugal force), it looks like a 1 km-above-baseline seasonal lift in the Arctic tropopause would effect a 3.4% additional refractive forcing of whatever-that-forcing-is-at-the-equator’s-tropopause in the Arctic. At the equator this refraction’s forcing is relatively constant. In the Arctic it is seasonal. But not as seasonal as my mid-latitude bias had assumed.

    I’ve used an astronomy program to make three movies of an annual cycle of the change in solar insolation from 12,000 km in altitude and 0°, 45°N, & 89°N. I lined them side by side across my monitor’s screen and watched them cycle to try to reprogram my bias. The one from 89°N had been particularly helpful relative to my mid-latitude bias. I feel a bit dimwitted to discover how less dim it is with this view from up north than I’d assumed. What might others see and think?

    And since twilight is represented by a program’s conventions, and those relative to the planet’s surface, this is still a perception-limiting view.

    My initial efforts at constraining what a 3.4% additional forcing might actually mean suggests that whatever the annual averaged amount of the forcing is, it has a doubling time of – plausibly – about 75 years … and this relative to an Arctic that is currently, on average, 3°C above baseline.

    Setting all this aside, and noting ATTP’s Twitter “like” of Tom Peck’s opinion piece on Brexit, a different way of approaching tipping points and being “slightly cautious” is asking the question of what is the upper temperature limit regarding neoliberislism’s CapitalismFAIL’s survival? Knuckle-draggers do have a way of making effective political moves.

    And think of this question in terms of a neoliberal strategy of weaponizing geoengineering (in the US this is now to be labeled “climate intervention”) in support of a [desperately needed!?!] Fourth Industrial Revolution.

    45, in his next administration, could pull this off for Wall Street. The $4 million of funding in the Continuing Resolution law last month could be cover for what the military already has planned and ready to make operational. We are withdrawing from the Paris Agreement … do I have to spin this conspiratorial thinking further regarding this question?

    Wouldn’t the eventual collapse of a fake green 4th Industrial Revolution be problematic if the “climate intervention” has been weaponized? What geoengineering strategies would not be significantly hampered by such a collapse? What negative emission technologies, which the promoted low emission pathways assume at scale, could be either developed, implemented, or maintained?

    Regardless of what one may feel about such questions, the current focus of the tweet storms reflected on here at ATTP could be a matter of science being played within game theory strategy. A 4th Industrial Revolution is, and Orwellianly so, dependent on geoengineering becoming politically tenable and dictatorially effected. Until Academia has an argument other than words it is vulnerable to being played in this expanding war of words.

    With the UK’s President for COP26 sacked by the PM, isn’t it more imperative than ever for UK’s academics to organize a zero carbon business plan strategy session for all of academia …through the University of Edinburgh [& virtually (low carbon)]? To have walk speak more forcefully than words?

    >

  45. Dave_Geologist says:

    John, similarly in parts of the Klamath forest. Disequilibrium of fire-prone forests sets the stage for a rapid decline in conifer dominance during the 21st century.

    Using a landscape simulation model, we estimate that about one-third of the Klamath forest landscape (500,000 ha) could transition from conifer-dominated forest to shrub/hardwood chaparral, triggered by increased fire activity coupled with lower post-fire conifer establishment. Such shifts were widespread under the warmer climate change scenarios (RCP 8.5) but were surprisingly prevalent under the climate of 1949–2010, reflecting the joint influences of recent warming trends and the legacy of fire suppression that may have enhanced conifer dominance.

    Large parts of the forest are already in a place where the natural vegetation is no longer forest. Only the presence of a mature forest is keeping the forest there, through ecosystem and perhaps microclimate feedbacks, along with active human management. If the forest goes it won’t come back, other than perhaps by human planting and other interventions until you get back to a stable forest. At current temperatures. Given the time it takes trees to grow, it may not even be worth trying if we’re heading for a 2-3 °C world this century. That is a tipping point in the same vein as the permafrost which has thawed at the top but the thaw hasn’t yet penetrated deep enough to release significant methane fluxes. But will in the end, even if we hold at current temperatures.

  46. Dave,

    ATTP, is the 375 W/m² vs. 310 W/m² to do with whether it’s a moist-stratosphere runaway or a dry-stratosphere runaway? They look suspiciously close to the c. 380 W/m² and c. 290 W/m² lines in Fig. 1 of my final reference.

    I’m not sure. I will try to find time to have a look.

  47. small,

    is there really such a thing as a true runaway state? Is Venus continuing to get hotter?

    No, it has reached an equilibrium. Even in the case of a planet undergoing runaway, it will either eventually lose the condensable greenhouse gas that has allowed it to reach the runaway state, or it will get warm enough that it starts emitting at wavelengths that allow the energy to be radiated to space. The runaway simply refers to the phase when the outgoing flux is limited and the surface warms without the system being able to reach some kind of energy balance.

  48. Greg Wellman says:

    I think there are some basic points and semantics that could be made clearer for the lay reader.
    1. Because of the T^4 Planck response, there is *always* an equilibrium.
    2. Feedbacks depend on circumstances and thus form “regimes”. E.g. the feedback regime with ice sheets is different from the one without. Even when there isn’t a real regime change, the T^4 response means the feedback will evolve as T changes (reducing feedback with higher T, just to be clear). That’s why #1 is true. Raise T enough and feedback drops, even if it was >1 at some point.
    3. A climatic “tipping point” seems best described as a transition between feedback regimes where temperatures just above the tipping point cause a higher feedback than temperatures just below. (The opposite change would be stable and thus not a “tipping point”.) Possible examples of climatic tipping points would be melting methane clathrates, and the cloud-loss-at-1200ppm effect that was much discussed about a year ago (e.g. https://www.quantamagazine.org/cloud-loss-could-add-8-degrees-to-global-warming-20190225/).
    4. Ecological tipping points don’t need to be climatic tipping points. The transition by fire of Australian (and Western American) forests to grassland (or other more open vegetation patterns) is an ecological, but not a climatic tipping point. (To be really technical, deforestation ecological tipping points tend to increase albedo, but also increase CO2, so they do have some mixed effect on feedback – just probably not significant enough to really be considered a climatic tipping point even if the feedback change is in the direction that could make it one.)
    5. The term “runaway” could be defined a couple of ways
    5.1. Any situation where feedback > 1 for some regime or portion thereof.
    5.2. As a pure Venus type runaway – the complete transition of all greenhouse gas reservoirs to the atmosphere.
    Correct me if I’m wrong, but there is no real agreement on 5.1 vs 5.2 definitions.
    6. Given that 3C will be very, very bad and 6C would be pretty much an extinction level event, it doesn’t really matter to humans whether a “runaway” runs for 8C like the cloud loss scenario suggests or runs for 100C or more like a Venus scenario.
    7. Given that 3C will be very, very bad and 6C would be pretty much an extinction level event, we can easily destroy our civilization without ever hitting a feedback > 1 tipping point, or any significant tipping point at all. Business-as-usual plus existing feedback can do it. Any tipping points, even below f=1 just increase the danger. All public-facing communication about feedbacks should emphasize that with just what we know now, we know we are destroying our future, and that all the unknowns do is increase the danger.

  49. D the G says: “the permafrost which has thawed at the top but the thaw hasn’t yet penetrated deep enough to release significant methane fluxes. But will in the end, even if we hold at current temperatures.” I think that may be true, but I think ATTP is correct that the thaw is probably going to take a long time and we should be able to study it as it happens and determine if it is reversible or non-reversible.

    I think it makes sense to be slightly to moderately careful about how we discuss these things. I really appreciate the quick Wellman lesson on these questions and the clarification on Venus equilibrium state post-runaway that probably wiped out liquid water at surface. Here’s an interesting link to the questions about water on Venus: https://www.nasa.gov/feature/goddard/2016/nasa-climate-modeling-suggests-venus-may-have-been-habitable

  50. David B. Benson says:
  51. John Hartz says:

    ATTP: In the climate science context, would the term tipping period generally be more appropriate to use than tipping point?

    Here’s an example of what I getting at. From a man-in-the-street perspective, the melting away of glaciers in Andes is occuring over a period of years. From the scientists perspective , it’s occurring in the blink of an eyelash in terms of geological time.

  52. John Hartz says:

    Speaking of the melting away of glaciers in the Andes…

    Using satellite data, scientists are documenting the inexorable melting of South America’s glaciers and ice fields, with Andean glaciers thinning by nearly three feet a year since 2000. The loss of ice poses a threat to water supplies and agriculture from Bolivia to Chile.

    Andes Meltdown: New Insights Into Rapidly Retreating Glaciers by Jonathan Moens, Yale Environment 360, Jan 30, 2020

  53. I am following ATTP’s lead on the question of the Andes glaciers. I think we need to be at least slightly careful about the way we discuss this matter. I read in the Moens piece that some, not many, glaciers are holding and a few are increasing, even though most are retreating and melting. I think the piece also indicated that one of the short term impacts of the melting would be an increase in available water supply, so I think it’s slightly careful to mention that fact. It’s not all bad news, right? More water is good, even if it may turn out to be short term.

    Finally, I did not see any time frame on when this melt will become a serious problem, nor anything to indicate that we know for certain that this melt is not reversible. A person named Luciana Juarez who operates in the tourism industry says, ““I know the glaciers are melting and I know that will be a problem in the future”

    Another person/source (again, I think, non-scientist) in the article is a 27 yo person named Lukas Garcia Reyes who says, “We’ve run into a wall,” he says. “There is no return, I think, because the climate has already changed.”

    These two sources are hardly a substitute for carefully, peer-reviewed science on what is happening in the Andes and what it truly means.

    I think this is exactly the kind of careless stories and reports that ATTP is suggesting that we should avoid when we can.

    I have a brother in law on vacation in that region right now. He is seeing all the sights and is pretty sure that things are not looking that bad in the region. I will check with him when he flies back to the PNW. I expect to see a lot of beautiful pictures of glaciers and mountains.

    I am torn between my own natural impulse to be quite concerned about all this, like JH and others here and the suggestion of reasonable folks like ATTP and my brother in law who say that we don’t really know for sure what any of this means. It makes sense to be slightly careful and acknowledge that changes will take a long time to develop, does it not?

    Cheers

    Mike

  54. David B. Benson says:

    https://www.google.com/amp/s/amp.theguardian.com/environment/2016/nov/28/shrinking-glaciers-state-of-emergency-drought-bolivia

    La Paz, Bolivia, and the neighboring communities depend upon glaciers for you water supply. This is no longer reliable.

  55. John Hartz says:

    Mike: For the record, your optimism is a tad too pollyannaish for my taste.

  56. In 2010, Chris Colose corrected Tony Heller (a.k.a. Steve Goddard) on a related subject, in the context of Venus’ runaway greenhouse warming. Heller was evading that warming, so he could falsely attribute more Venus’ warm temperature to atmospheric pressure:

    https://chriscolose.wordpress.com/2010/05/12/goddards-world/

    Yet almost of a decade later in 2019, Potholer54 (a.k.a. Peter Hadfield) had to repeatedly correct Heller’s distortions on non-runaway positive feedback. Of course, Heller continued to repeat the same distortions anyway, even after Potholer54’s rebuttal. Amazing.
    Still, the discussion was still useful since Potholer54 provided a nice, basic introduction to non-runaway positive feedback in the context of glacial cycles:

    from 5:25 to 6:27 :

  57. Dave_Geologist says:

    Thanks for the NASA/Venus link mike. I suspect that a lot of this is still up for grabs as people appear to have been addressing it with 3D time-resolved models for less than a decade, and the early ones I quoted up thread from 2013 showed that previous 1D equilibrium models were misleading. Moving fast though: from where Earth’s climate model was in the late nineteenth century in the 1980s, to where Earth’s climate model was in the 1980s-1990s by the 2010s.

    I suspect the answer will be “it’s complicated” and “it depends”. Especially given the NASA paper’s finding that topography and land/sea distribution matter, which we know little or nothing about on early Venus, let alone exoplanets. I’ll repost a couple of links: Emergence of two types of terrestrial planet on solidification of magma ocean. This one made a distinction between Type I planets which cool fast enough to have a solid surface and water ocean and become like Earth, unable to have a runaway greenhouse because insolation is below the radiative limit for a steam atmosphere; and Type II planets (early Venus?) where the steam atmosphere forms shortly after accretion while the surface is still hot, perhaps molten, and delays cooling by many millions of years because insolation is above the radiative limit for a steam atmosphere – you have to wait for the water to be stripped out before cooling can resume.

    I speculated that you could have an intermediate, presumably with insolation close to the limit and perhaps crossing the limit as the Sun warms, where the surface cools and oceans form, but the oceans later boil off and lead to a dry-stratosphere runaway (the blue line in Figs. 1 and 5 of The runaway greenhouse: implications for future climate change, geoengineering and planetary atmospheres). That may have been Venus’ fate from your link, and will presumably be Earth’s fate, before we get engulfed as the Sun goes red-giant (they also generate a moist-stratosphere scenario, one of their four simulations). A potential tipping-point into that state might be something like the Late Heavy Bombardment, as investigated here: Water loss from terrestrial planets with CO2-rich atmospheres – although again it’s complicated and they found that impacts which put a lot of water into the stratosphere also eject a lot of non-condensable atmosphere. So that might not work for Venus which has retained a thick atmosphere.

  58. Dave,
    I had a quick look at the runaway greenhouse effect paper. The increased threshold (375W/m^2 rather than something like 300W/m^2) seems to be because the earlier work used 1D models, and they’ve managed to simulate this using a 3D model. I haven’t quite understood what the difference is, but it seems to be due to clouds (as always 🙂 ).

  59. Dave_Geologist says:

    Ah yes, thanks ATTP. As always, clouds. The non-saturation of the Hadley cells was also a factor IIRC, allowing some windows around the tropics where IR could still escape, so the 3D model can emit more than the 1D model which assumes saturation.

    Exoplanets (and our neighbour planet) are fascinating 🙂 !

  60. Dave_Geologist says:

    Here’s a link to another Goldblatt paper. I like his exposition and clear but quantitative cartoons – YMMV. I’m assuming it’s his influence as lead author and common factor even if a co-author drew them. Low simulated radiation limit for runaway greenhouse climates. It goes through the steps of adding components to a 1D model, and shows I was wrong in assuming you’re stuck in a dry-stratosphere greenhouse until surface heat can escape directly to space. Fig. 1 shows that for a red-hot surface, but still with a cold trap, the upper troposphere radiates in the 4 μ window. That leads to a stable “escape” from the greenhouse, albeit one with a rather uncomfortable 1750 K surface temperature. Absent clouds, we’d be very close to a runaway greenhouse even with pre-industrial CO2 levels. With net negative feedback from clouds, we’re stable at RCP8.5 and even at 3,000 ppmv CO2, but we can go into a runaway at 30,000 ppmv CO2. But by that stage, we’d have seen 50°C warming, so whatever was emitting those final tranches of CO2 into the atmosphere, we can be confident it wouldn’t be a human civilisation anything like today’s. So it’s probably fair to say it’s impossible through anthropogenic emissions, because we’d drive ourselves extinct before we succeeded 😦 .

    The actual numbers are possibly moot if 3D models are showing that it’s even harder to induce a runaway greenhouse, but it’s reassuring that even simple models show we can’t do it with any feasible level of CO2 emissions, and that more sophisticated models show that even more strongly. Also that both are showing we won’t enter a moist-stratosphere greenhouse and lose our water. Now all we have to worry about is that warm Sun in a billion years or so 😉 .

  61. smallbluemike said:

    “A runaway greenhouse effect is when there is enough of a greenhouse gas in a planet’s atmosphere such that the gas blocks thermal radiation from the planet, preventing the planet from cooling and from having liquid water on its surface.”

    Obviously not completely.

    I’m surprised that this group doesn’t understand that Arrhenius rate laws limit the amount of runaway possible. https://www.nasa.gov/centers/ames/news/releases/2002/02_60AR.html

  62. John Hartz says:

    I’m not sure that this article, published today, is telling us anything new., It does, however, contain a graphic showing how the climate sensitivities of a selected group of GMCs compare with each other. I have heretofore not seen such a graphic.

    Climate Models Are Running Red Hot, and Scientists Don’t Know Why by Eric Roston, Bloomberg News, Feb 3, 2020

  63. JH said :

    “I’m not sure that this article, published today, is telling us anything new., It does, however, contain a graphic showing how the climate sensitivities of a selected group of GMCs compare with each other. I have heretofore not seen such a graphic.

    Climate Models Are Running Red Hot, and Scientists Don’t Know Why”

    Steve Easterbrook tweeted that the article was fairly reported. What’s puzzling is why the scientists can’t explain the increase. I know that with deep-learning neural network models it’s often difficult to reverse engineer a mechanism, but with a parametric model it should be straightforward — change the parameters systematically via a sensitivity analysis.

  64. I do the pollyanna thing on this website because the host appears to be committed to that kind of discussion. I have been described as a glass half empty guy elsewhere.

    I think the pollyanna read on things is encouraged here, so I am trying to get in line and amplify that pov. I have taken the extra step of quoting our host to make it clear that I am amplifying that pov.

    Here’s a quote from ATTP to consider:

    “There is the possibility of a global tipping point, but this is seen as very unlikely. However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice.

    If we were to cross any of these tipping threshold, then the changes would further amplify the warming (through either releasing additional CO2, or methane, or changing the albedo) and – in the case of the ice sheets – would lead to substantial sea level rise. There are a few things to bear in mind, though. The timescales are typically long; if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie; we could already have crossed some, or might not do so unless we were to warm substantially. Additionally, there is still debate as to whether or not some of these are truly irreversible; if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ”

    Global tipping point? very unlikely.
    Timescales are typically long, taking centuries to manifest
    We don’t know where the tipping point thresholds might lie or if they are irreversible.

    Do these ideas/assertions strike you as too pollyannaish? Whose ideas are these?

    Keep up the good fight, John H! I appreciate your analysis.

    At Paul Pukite: the runaway definition is not mine, it was a cut and paste from the wikipedia source, link was provided above.

    Mike

  65. John Hartz says:

    Another very thought-provoking article by David Roberts and perhaps the basis for a new OP on this site.

    Assessing climate policy requires much more than science.

    Climate scientists are not priests or prophets</strong by David Roberts, Energy & Environment, Vox, Feb 3, 2020

  66. “It’s like asking physicists to judge a dance competition and hearing that one of the dancers is “backed by physics.””

    not much to do with “feedbacks, runaway and tipping points”, JH, but a keeper analogy.

  67. angech says:

    feedbacks, runaway, and tipping points
    Donald Trump 31,386 97.15% 38
    Yes, I know, poor taste.
    But I thought a 97% rate meant a consensus?

  68. dikranmarsupial says:

    “But I thought a 97% rate meant a consensus?”

    why do you think it doesn’t mean a consensus (among Iowan delegates) here?

    BTW, I think this is an indication of insufficient negative feedback. Seriously if the Republicans can’t field a better candidate than Trump, they have serious problems.

  69. smallbluemike said:

    “At Paul Pukite: the runaway definition is not mine, it was a cut and paste from the wikipedia source, link was provided above.

    Mike”

    I’m so very sorry, didn’t realize you were quoting a Wikipedia source.

    One thing that has been drilled in our heads concerning the earth’s atmosphere is that the infrared radiation can escape once the concentration of GHGs thins out enough. I would think this happens on Venus as well. So no atmosphere that shows a diminishing density profile with altitude can completely block thermal radiation from a planet. And that the CO2 also has a specific window with respect to the infrared spectrum, so it can’t by itself block all the wavelength components of thermal radiation from the planet.

    http://lasp.colorado.edu/~espoclass/ASTR_5835_2015_Readings_Notes/Titov_Et_Al-EVTP.pdf

    “2.1 Venus as Seen From Space
    The spectrum of Venus when observed from space has two components: reflected solar radiation and infrared thermal emission. The first component dominates in the UV through the near-infrared range (0.2–4. µm) over the sunlit hemisphere, while the second one prevails at longer infrared
    wavelengths (4–50 µm). Figure 1 shows the mean spectrum of each of the two components together with the night side emission spectrum.”

    I should probably update the Wikipedia page with an asterisk if I can bear with the grief I might get.

  70. Dave_Geologist says:

    97.15% of what, angech?

    Of course, who the consensus is among matters. That’s why the various consensus studies stratify the scientists involved according to their specialist-subject expertise. A consensus about a branch of science among scientists might be quite different from the consensus among a bunch of amateurs who think the Universe was made from nothing in six days. A consensus among Cornwall Alliance signatories who’ve also signed up to a statement that their religion trumps science is valuable as an insight into the thinking of fundamentalist Christians, but has negative value when it comes to a branch of science they’ve explicitly said they’ll deny, regardless of the evidence.

    As George Carling said:”never underestimate the power of stupid people acting in large groups”. A wise person might give little credence to the consensus among such a group, however large it might be and however strong the consensus. They would of course be very aware of the power of such a group to do things which have bad consequences, so would not completely discount or ignore them. Maybe oppose them or work on mitigations.

  71. Dave_Geologist says:

    Paul, rate laws don’t matter for a 1D equilibrium analysis like Goldblatt’s. It’s immaterial how long it takes to get from one stable state to another. The point is that there is a runaway between the two stable states. It might be a slow runaway, but if it ain’t gonna stop until the new equilibrium at 1750K surface temperature, we’d better find ourselves another planet to live on.

    They do matter for temporally resolved FD models, but I’d be astonished if they don’t include rate laws, activation energies, latent heat etc., at least in some parameterised form. Otherwise how could they model the formation of clouds?

    I see I missed out the link to the second Goldblatt paper. Here it is: Low simulated radiation limit for runaway greenhouse climates. The purple line in Fig. 1c shows the bistable (actually tristable) state for a planet with an Earth-like cloud cover. So per my comment further up, the runaway greenhouse is indeed a bifurcation rather than a tipping point, like Snowball Earth. Or rather, it’s a tipping point which is also a bifurcation. Not all tipping points are bifurcations though.

    As I said, I do recommend those two Goldblatt papers. I had thought I understood the runaway greenhouse, but I was envisaging it as a monotonically increasing mapping which just gets very steep. Now I see that I didn’t. I’m sure I’d read the Skeptical Science page before, but Goldblatt has nicer, more intuitive diagrams.

  72. Joshua says:

    Typical of “skeptics,” angech cherry-picks Trump’s performance in Iowa and ignored
    his performance in “Kansas.”

  73. Dave said:

    >”Paul, rate laws don’t matter for a 1D equilibrium analysis like Goldblatt’s.”

    I’m giving the point of view of a materials scientist who has done plenty of work related to vapor pressure process control in a lab environment (lots of cites if needed). There’s a concept of a set point whereby one can control via a feedback system the pressure of a gas. What I have done is apply these ideas to a system where the positive feedback is the catalytic C02/H20 warming interaction and the negative feedback is the natural Planck response. This is just an algebraic way of solving the climate bistability problem that Goldblatt refers to (the snowball earth vs non-snowball). To other material scientists, they would probably say “meh” to what I published, but evidently it’s not well known among other disciplines. If people would take a look at this then perhaps there would be less confusion about understanding why a positive feedback doesn’t automatically equate to a runaway effect. This is especially problematic among D-K afflicted electrical engineers who see positive feedback and assume the worst in terms of a runaway instability — since positive feedback in a electrical circuit is typically direct.

    Bottom-line, are we interested in communicating principles of climate science in straightforward ways or not?

  74. no problem, Paul. No need for apology, I just wanted to clarify. I say enough dumb stuff on my own to warrant some regular criticism, but probably not on that one. Good luck with the edit

  75. at ATTP: are you really confident that the tipping points and changes are going to be as slow and manageable as this post suggests? I am starting to waver with my support for your position on that.

    https://m.phys.org/news/2020-02-arctic-permafrost-greater-role-climate.html

    Some of this stuff looks like it could be fast enough to be a real problem and reversibility seems like a long shot.

  76. This is a fascinating rationale by Gavin Schmidt for why it’s difficult to pinpoint cause and effect in the “red hot model” findings.

    To answer my earlier question as to why they can’t just systematically change the parameters to pinpoint the causal factors, it looks as if #2,3,4 (coupled emergent effects) and #7 (limited time and resources) are issues. He summed it up with “odd things happen” #10 #11

  77. Dave_Geologist says:

    Of course I’m interested in communicating principles of climate science in straightforward ways Paul. That’s why I referred to the Goldblatt papers, which have some nice simple-but-quantitative diagrams. And are about a normal Earth to a red-hot steam-atmosphere Earth, not Snowball Earth.

    As I said YMMV. I’ll leave it to others to decide whether Goldblatt’s explanation is more or less comprehensible, at least to non-materials-scientists, than your analogies. If your analogy says the physics in Goldblatt’s papers is wrong (other than the simplification intrinsic in a 1D model), you won’t convince anyone with what may seem to them a somewhat tortured analogy. You’ll convince them by finding the mistake in the physics. Ditto for the 3D models, but there you might also find a mistake in the parameterisation, in the gridding, or in the solver. Again, you’ll need to get under the hood to do that.

    I know perfectly well that a positive feedback does not equate to a runaway, and neither I nor Goldblatt said it does.

    Limit 1, the black body upper limit, is the maximum radiation that any planet of given surface temperature can emit; this varies with temperature. It does not lead to a runaway greenhouse, but is included for context. Limit 2, the moist stratosphere upper limit, is the maximum amount of radiation that can be transferred by a moist stratosphere; this is invariant with temperature, and so can lead to a runaway greenhouse. Limit 3, the moist troposphere asymptotic limit, is the amount of radiation that a thick, pure water vapour atmosphere will emit; the radiation from any thick water-rich atmosphere will tend towards this asymptotic limit. It is invariant with temperature, and so can lead to a runaway greenhouse.

    Depending on which diagram you’re looking at, you can express it as a situation where the climate sensitivity is infinite, one where the natural Planck response saturates at an outgoing flux which is constant over some (in this case very broad) surface temperature range, or one in which the net outgoing flux decreases with increasing surface temperature (past the humps in Fig. 4f of the second paper, where the runaway is caused by increased solar irradiation with a non-condensable GHG content comparable to today’s). All of which are positive feedbacks, but not just any old positive feedback.

    Note: “invariant with temperature” means over a certain temperature range, not forever. That’s so obvious from the diagrams that Godblatt didn’t mention it, and is also implicit in the text saying you escape from the runaway when you get hot enough to expose a different part of the water vapour spectrum (what I referred to as changing the rules).

  78. Dave, perhaps stick to the earth. What I provided is perfectly suitable for explaining the snowball/no-snowball bi-stable set-points. It may also help in explaining a tri-stable situation if the earth’s glaciation regimes are considered, whereby the snowball doesn’t cover the earth completely

    “… than your analogies.”

    What do you mean analogies? Scientists such as Goldblatt aren’t using anything other than conjecture, as they certainly can’t recreate any of these conditions in a lab setting. My approach is simple, just solving a quadratic equation assuming the known climate sensitivities and the rate laws for GHGs.

  79. John Hartz says:

    In his recent Guardian op-ed, Michael Mann addresses whether or not a societal tipping point has now been reached…

    Australia’s horrific bushfires could be the catalyst that pushes the world to a mass recognition that it’s time to act.

    If there’s a silver lining in the clouds of choking smoke it’s that this may be a tipping point, Opinion by Michael Mann, Comment is Free, Guardian, Feb 2, 2020

  80. John Hartz says:

    ATTP: From a quantum physics perspective, can an observer recognize a tipping point while they are in it? Will observing it change its properties? 🙂

  81. John Hartz says:

    On the good news front…

    Thunberg, 17, has encouraged students to skip school to join protests demanding faster action on climate change, a movement that has spread beyond Sweden.

    Teenage climate activist Greta Thunberg nominated for Nobel Peace Prize, AP/NBC News, Feb 3, 2020

    I rather doubt the US Pretend President will be nominated this year — or in any year for that matter.

  82. John Hartz says:

    Lest we sweep ocean acidification under the rug…

    Not everyone would consider 150-year-old plankton specimens a treasure with “cutting-edge” research potential. But that’s precisely what Lyndsey Fox thought when she discovered a cache of single-celled, shell-building foraminifera deep in storage at London’s Museum of Natural History. Now, the Kingston University micropaleontologist and colleagues have shown that the samples, collected during the pioneering 1872–76 expedition of the HMS Challenger, hold valuable insights about modern-day climate change: Their shells are up to 76% thicker than those of today’s foraminifera, which are thinning in our increasingly acidic oceans.

    Samples from famed 19th century voyage reveal ‘shocking’ effects of ocean acidification by Erin Malsbury, Science Feb 3, 2020

    Has the oceanic component of the biosphere undergone any tipping points to date?

    We must also keep in mind that the effects of what happens in the global ocean system do not always stay within that system, e.g., the production of oxygen be micro-organisms such as plankton.

  83. Dave_Geologist says:

    So, no line-by-line spectral absorption calculations, Paul? No Rayleigh scattering? No line-by-line emission? None of that physics thingie this site is about?

    Perhaps you should read the papers before dismissing them?

    *Sigh* At least llearned something over the last few days.

    My last word on this, but you carry on if you want.

  84. izen says:

    @-JH
    “Has the oceanic component of the biosphere undergone any tipping points to date?”

    One candidate may be the disappearance of cod from the Canadian grand banks in the Atlantic.
    While that may not be a climate impact, (?) it does show one key aspect of tipping points.
    When the initiating cause is removed (depletion by fishing) the condition does not reverse, it continues to the new stable state.
    (No cod)

  85. Ben McMillan says:

    FWIW I found Goldblatt’s papers interesting, and pretty comprehensible, and it isn’t a topic I know that much about.

    Complaining that planetary physics ‘can’t be recreated in a lab’ is a bit odd. Although it makes me wonder if you could simulate a scaled planetary atmosphere on the inside of a rotating tank with a strong internal heat source. Or in a very, very tall building in a large tube. A well-insulated mineshaft maybe?

  86. Dikran Marsupial says:

    The characterisation of electrical engineers is pretty unfair as well – they get lots of lecture time on feedback systems and know how to determine if such a system is unstable (there are even jokes about it). Assuming that your background gives insight into other fields, which they will benefit from is a recipe for D-K syndrome, and this sort of “my field is better than yours” scoffing does not engender confidence IMHO.

  87. John Hartz says:

    The latest on sea level rise along US coastlines,,,

    The pace of sea level rise accelerated at nearly all measurement stations along the US coastline in 2019, with scientists warning some of the bleakest scenarios for inundation and flooding are steadily becoming more likely.

    Of 32 tide-gauge stations in locations along the vast US coastline, 25 showed a clear acceleration in sea level rise last year, according to researchers at the Virginia Institute of Marine Science (Vims).

    The selected measurements are from coastal locations spanning from Maine to Alaska. About 40% of the US population lives in or near coastal areas.

    The gathering speed of sea level rise is evident even within the space of a year, with water levels at the 25 sites rising at a faster rate in 2019 than in 2018.

    Sea level rise accelerating along US coastline, scientists warn by Oliver Milman, Environment, Guardian, Feb 3, 2020

  88. John Hartz says:

    izen: I concur with your suggestion that the disappearance of cod off of the grand banks of Canada might be a tipping point. It also negatively impacts the ability of humans to sustain themselves. Can cod be farmed?

  89. dikranmarsupial says:

    Ben “Complaining that planetary physics ‘can’t be recreated in a lab’ is a bit odd.”

    I gather suitable lab equipment is available from Magrathea, however it requires a moderately large laboratory to use effectively.

    This is a common contrarian argument. You can demonstrate absorption of IR by CO2 in a jar in the lab, but that isn’t really how the greenhouse effect mechanism actually operates. I don’t think the actual mechanism can be demonstrated in a lab as you would need a test-tube large enough to have convection and a substantial temperature difference top-to-bottom due to the lapse rate.

  90. at ATTP: I agree with you that it will take a long time, like centuries in many instances, for the FULL EFFECTS of the changes to manifest, but if the effects that are felt and measured during the transition tipping period (I like that better than tipping point) are clearly harmful, maybe we should all take a slightly less careful approach to how we describe this predicament. What do you think? Is the tone of your post on this perhaps just a little too sunny?

    I think JH, DBB and others have presented some compelling arguments for alarm. Would you agree? Are you alarmed about the changes in the climate and ecosystem?

    Cheers

    Mike

  91. at JH, re the disappearance of cod, etc: I don’t eat fish anymore if I can help it. I feel a kinswhip with the folks who used to gather ice from the Andean glaciers but don’t think they can take more from the glaciers now. I just can’t take anything more from the ocean fisheries and ecosystem. I can’t eat cod or salmon or shellfish anymore and feel good about it. But that’s just me, ymmv.

    The collapse of the fisheries really makes me sad, but not because I may not be able to get cheap tasty fish filets whenever I want. Those days are gone for me and I don’t think they are coming back. I can try to adopt ATTP’s sanguinity about the situation, but it’s hard to sustain.

  92. Dave said:

    “So, no line-by-line spectral absorption calculations, Paul? No Rayleigh scattering? No line-by-line emission? None of that physics thingie this site is about?”

    The approach subsumes the spectral details via applying the logarithmic climate sensitivity. You really need to look at our published work before casually dismissing it.

  93. Ben said:

    “Although it makes me wonder if you could simulate a scaled planetary atmosphere on the inside of a rotating tank with a strong internal heat source. Or in a very, very tall building in a large tube. A well-insulated mineshaft maybe?”

    So a lab-scale tank can emulate the effect of gravity to balance the centrifugal and centripetal forces? This idea reminds me of the Plumb-McEwan tank experiment that was designed to emulate the equatorial QBO standing wave. The apparatus was a cylinder instead of in the real case a sphere that held a stratified equatorial ring layer aloft by gravitational balance. So for the Plumb-McEwan experiment, the geometry was off and the forces weren’t radially inward but along the axis of the cylinder length. Even with that mismatch, their experimental results have often been cited to justify some aspect a QBO model or to explain the radiosonde measurements. Interesting to how far one can contort the resemblance from the actual situation.

    Plumb, R. A., and A. D. McEwan. “The instability of a forced standing wave in a viscous stratified fluid: A laboratory analogue of. the quasi-biennial oscillation.” Journal of the atmospheric sciences 35.10 (1978): 1827-1839.

  94. John Hartz says:

    Mike: Thanks for sharing your personal decision to not eat seafood.
    That response and your response to ATTP tells me you are not as Pollyannaish as I had thought.
    Mea Culpa,

  95. David B. Benson says:

    John Hartz, one could farm cod but that nobody does suggests there is no profit in doing so.

    smallbluemike, there is plenty of farmed salmon. Also some wild-caught species. You might care to avoid anything that bottom trawlers bring up.

  96. at DBB: salmon is a wild animal. It should not be farmed. I don’t have any interest or appetite for eating salmon flesh built from fish pellets.

  97. Dave_Geologist says:

    Paul, you do know that the logarithmic temperature response to CO2 concentration is not a direct consequence of physics, but a curve-fitting approximation which works at moderate concentrations like now or pre-industrial but breaks down at low and high CO2 concentrations? One that was discovered by doing the physics then fitting an empirical curve to the results. And of course H2O may or not be approximately logarithmic at moderate concentrations for the same reasons, but I very much doubt if that is the case in a steam atmosphere. In fact I know that’s not the case because physics-based approaches like Goldblatt’s have done the hard calculations at high concentrations, and if it remained logarithmic you couldn’t get a runaway. And if you didn’t have physics-based interaction between two GHGs you couldn’t get the overshoot and hump I referred to. Perhaps you should revisit your logarithmic assumption. Or post links to your papers so I can read them.

    I know I said I was finished, but logarithmic-for-ever is a popular misconception, sometimes used to say climate science is false because it gives silly results at zero concentration, so it’s worth correcting. The answer, of course, is that if you do the physics it stops being logarithmic before you reach that point.

    As an aside, the same misconception was often displayed by visitors to my old field regarding the (negative) exponential plot of ocean-floor depth with age. It’s a square-root function at early time and linear at late time, due to the geometry of a very narrow ocean, and to mineral reactions and phase changes under deep burial. Which, if left to their own devices for long enough, can result in a density inversion and interesting things like delamination or initiation of subduction.

  98. Dave, Believe it or not sometimes it’s really just about trying to simplify our understanding and therefore our intuition.

    Huang, Y. & Shahabadi, M. B. Why logarithmic? A note on the dependence of radiative forcing on gas concentration. Journal of Geophysical Research: Atmospheres 119, 13,683-13,689 (2014).

    “Understanding the logarithmic dependence of radiative forcing on atmospheric gas absorber concentration is not only academically interesting by itself but also shed light to understanding climate feedback and sensitivity. The logarithmic nature of the forcing dependence allows us to efficiently estimate the radiative forcing and feedback using analytical methods. The analysis here suggests that such analytic methods can be applied to not only broadband but also spectrally resolved radiation.”

  99. Dave_Geologist says:

    Over what concentration range Paul? An 8x perturbation of 280ppm is 2240 ppm. To drive a CO2 runaway greenhouse needs ten times that (actually more than ten times, because the 3D models require a significantly higher insolation threshold than Goldblatt’s 1D models). Absolute humidity of water vapour is in the order of 1%; a steam atmosphere could have 50% or 100% water vapour.

    Thanks for the link. They may have an alternative explanation to the textbooks, but I’ll hold fire on accepting it until it becomes the consensus. 22 cites in five years, a significant number self-cites, suggests it’s not yet mainstream. And from a quick skim they seem to be saying the textbook explanation isn’t enough because it doesn’t explain why it also applies to monochromatic radiance (another self-cite). So the textbook explanation is fine for actual CO2 and water vapour spectra? And I note that they demonstrate the logarithmic relationship with a MODTRAN analysis… IOW exactly what the runaway authors do. And yet in their hands it can generate runaways. At partial pressures orders of magnitude higher, where by implication the logarithmic relationship must break down.

    Approximations are fine over the range where they work. As I said, we don’t have to worry about a runaway until the Sun gets hotter, because we’d have rendered the planet uninhabitable long before we could get to the tipping point for runaway through our own actions. Literally uninhabitable. You’d need a spacesuit to survive outdoors, even at the poles. That doesn’t mean that there’s no tipping point, or that it’s not worthwhile to investigate it and understand it, or indeed to consider how other planets might be different, which is where I started out. Nor does it mean that the logarithmic assumption isn’t fine for the range of interest for climate planning. I never said otherwise. It’s just not fine for deciding whether or not a runaway can happen at concentrations which are not accessible to and won’t ever be accessible to the human race.

    In a similar way the exponential subsidence model is fine for well over 90% of the world’s oceanic crust. It’s just not fine in newly-forming oceans, in the vicinity of mid-ocean ridges, and in the small part of the Pacific which has very old oceanic crust. It probably wouldn’t be fine in a different Earth, for example one with a single supercontinent with lots of old oceanic crust around it and with most spreading happening in new intracontinental rifts and infant oceans. That second situation might be of great interest to me as a geologist, but of no interest to the editor of the next edition of the Times World Atlas.

  100. Dave_Geologist says:

    And from the second paper: Logarithmic radiative effect of water vapor and spectral kernels

    Applying logarithmic scaling in the water vapor absorption bands where absorption is strong and linear scaling in the window region where absorption is weak can generally constrain the error to within 10% of the overall OLR change for up to eightfold water vapor perturbations.

    IOW horses for courses. Over specified ranges. Hmm, wonder what would happen in the water vapour absorption bands where absorption is strong if you made the water vapour concentration really really small? Or in the window region where absorption is weak if you made the water vapour concentration really really big?

  101. The Huang paper references an Emission Layer Displacement Model, which is related to classes of calculations used by us spectroscopists. The gist of the idea is that the logarithmic dependence arises from the integration of a differential transmittance along a length (in this case the atmospheric layer). The differential transmittance can be described by ΔL/L where L is the depth of the layer. Integrating this over the entire length, one gets log(L) and since L will vary as an effective optical depth with increasing concentration, the logarithmic dependence arises. Huang goes through a more detailed calculation than this intuitive model provides, but the essential idea is that the log comes from the path traversing along the scattering cross-section.

  102. Paul,
    Can I clarify? Are you suggesting that the logarithmic relationship applies across the full range of possible concentrations?

  103. Yes, I think it goes from one path end-point to the other in Huang’s Emission Layer Displacement Model. A different final concentration will give a different path end-point. Like I said, I have seen this kind of logarithmic derivation for spectroscopic methods involving scattering many times, and was not surprised that it is used here.

    Yet I also though it might not be general because CH4 and N2O are not modeled by a logarithm but by a square-root dependence. A square-root has a vague similarity to a log function yet doesn’t have a singularity at 0, which may be why they apply it for those GHGs.

  104. Dave_Geologist says:

    So it’s a curve-fit Paul. Like the linear fit they propose for part of the water-vapour spectrum. Which works for the parameter range where the curve(s) fit the physics, but not where they don’t.

    I must have a dig around and see whether anyone has 3D-modelled the mixed-GHG atmosphere, to see if the temperature thresholds change or just the insolation threshold.

    The ones with CO2-driven outgoing-emission-overshoot would be a wicked tipping-point to identify, even if we could maintain a civilisation in so warm a world. In those, the tipping point is tens of degrees below the start of steam-driven runaway where you begin boiling the oceans. It’s at the hump, where climate sensitivity essentially becomes negative: between there and the asymptote, warming increases rather than decreases the energy imbalance, even at constant insolation. Fascinating. Like those meta-materials with an “impossible” negative Poisson’s Ratio. I love it when science is counter-intuitive.

  105. Dave said: “So it’s a curve-fit”

    Name some aspect of experimental science that requires matching data to a closed-form analytical theory that is NOT a curve fit. In fact, everything that is beyond a point fit (such as estimating Einstein’s cosmological constant) is classified as a curve fit, whether it’s a straight line, curved line, surface, curved surface, or any multidimensional manifold. They are all in some sense analytical curves that need to be fitted to real world data if the theory is to gain any acceptance. The term “best fit” or “model fit” is often used instead of curve fit to describe this process — but guess what — Wikipedia redirects “best fit” to “curve fit” and “model fitting” to “curve fitting” !

    Of course heuristic curve fitting is different, as the physics I provided is not based on a heuristic but on a real physics-based model that Huang derived from considering a differential transmittance.

    That’s kind of a pet peeve of mind when someone suggests “curve fitting” as a backhanded compliment.

  106. dikranmarsupial says:

    PP wrote “Name some aspect of experimental science that requires matching data to a closed-form analytical theory that is NOT a curve fit.”

    you are missing out the important bit:

    Dave wrote “Which works for the parameter range where the curve(s) fit the physics, but not where they don’t.”

    There is nothing wrong with curve-fitting, provided that you know that is what you are doing and don’t try and pass it off as anything more than that without good argument/evidence (c.f. Nikolov – who argues in his paper that his candidate curves have physical justification).

  107. dikranmarsupial says:

    “Name some aspect of experimental science that requires matching data to a closed-form analytical theory that is NOT a curve fit. In fact, everything that is beyond a point fit (such as estimating Einstein’s cosmological constant) is classified as a curve fit,”

    IIRC there was no analytic theory for Einstein’s cosmological constant when it first appeared in his equations – he added it because he wanted to have a steady-state universe (for which he had no real observational or theoretical justification). It was a heuristic term added to the physics.

  108. Dave_Geologist says:

    Paul, as an example any process following first-order kinetics is exponential with time. Not as a result of curve-fitting but because the exponential falls out via basic maths and the definition of first-order kinetics. Many chemical reactions, and radioactive decay, for example. The textbook explanation for logarithmic forcing, OTOH, is a fortuitous coincidence driven by peak-broadening which has a host of interacting causes, none of which inherently say “logarithmic”.

    Of course you could argue that memory is introduced by the closeness of the reactants in the carrying medium or by disturbance of the carrying medium, or that there are interactions between atomic nuclei or between nuclei and emitted particles, meaning that the process is not truly, at the limit, first-order. A case in point would be reaching critical mass. But you still have the assurance of knowing that it is fundamentally exponential, with secondary perturbations, and that you can predict a long way out-of-sample in the expectation that the secondary perturbations will be small relative to the exponential. And that it’s not, for example, a part of a logistic curve which just looks exponential.

    The curve-fitting comment was not meant as a back-handed compliment. I was emphasising that you can’t assume it applies across all concentrations or partial pressures, and that the authors you quoted followed the process (1) make the measurements or do the MODTRAN calculations; (2) see what sort of curve fits; (3) come up with a physical rationale for why that curve fits, at least in that part of the parameter space.

  109. “IIRC there was no analytic theory for Einstein’s cosmological constant when it first appeared in his equations”

    Thanks for that correction. Since the cosmological constant is more of a fudge factor heuristic than a part of a theory, the speed of light c may be a better candidate as a point fit. Yet even that has been estimated by fitting with respect to many different points on a curve:

    “In 1728, English physicist James Bradley based his calculations on the change in the apparent position of the stars due Earth’s travels around the sun. He put the speed of light at 185,000 miles per second (301,000 km/s), accurate to within about 1 percent.”

    Another kind of point fit is on predicting the position and size of an unknown astronomical object. Yet this is also based on seeing an anomaly on some data curve that doesn’t fit the theory predicted from known data.

  110. Dave said:

    “(2) see what sort of curve fits”

    I rest my case.

  111. John Hartz says:

    I believe the following excerpt from an article by Steve Hanley (CleanTechnica) is directly relevant to the ongoing discussion among Paul Pukite and others on this thread…

    The most recent peer reviewed study, Mann says, was published by Rogelj et al in Nature in 2016. But that study used a simplistic climate model that did not take into account what Mann calls nonlinear factors — changes in climate dynamics that are exponential rather than arithmetic. They are often called feedback loops, in which small changes contribute to and reinforce even more changes.

    We have seen a sobering example of the importance of these feedback mechanisms here in Australia where I am currently on sabbatical. In the catastrophic fires that have engulfed the continent (which were exacerbated and amplified by unprecedented heat and drought made possibly by climate change), roughly twice as much carbon escaped into the atmosphere as was produced by all of fossil fuel burning in Australia over the last year. </em

    These sorts of amplifying “carbon cycle” feedback mechanisms (and this is just one example–there are many others including, for example, the potential release of frozen methane in the Arctic with warming) are not accounted for in the simple sorts of projections that Hausfather and others are using here. It is very likely that these feedback mechanisms will add substantially to the warming over the next century. </em

    Combine that with the fact that the most recent (“CMIP6”) IPCC climate models seem to be showing the potential for considerably greater warming than the previous generation (“CMIP5”) of IPCC models, and in my view, it is very difficult to rule out warming in excess of 4C under “business-as-usual” climate policies. Only with very strong mitigation efforts and rapid reduction of carbon emissions can we avoid such a scenario with a high degree of confidence. </em

    Finally, let’s not forget that even a 3C warmer world would be catastrophic. Here in Australia, we’re already seeing the catastrophic impacts of less than half that much planetary warming. </em

    Most of this critical context has been lost in the recent discussion. </em

    There is some good news here. The numbers show that escalating efforts around the world to decarbonize our economy are starting to pay dividends. We’re starting to bend that emissions curve downward. But we need to reduce emissions by a factor of two over the next decade and bring them down to zero in a matter of a few decades if we are to avert catastrophic climate change impacts. We have to get off fossil fuels far more quickly than we’re on track to do under current policies. </em

    This latest commentary doesn’t change that at all. </em

    Worst Case Climate Change Scenario Is Scary, But The Reality Could Be Even Worse by Steve Hanley, CleanTechnica, Feb 5, 2020

  112. dikranmarsupial says:

    “Since the cosmological constant is more of a fudge factor ”

    It was at the time, Einstein removed it, and it was since put back in again, now we have some theory/observations that suggests it belongs there.

    “Since the cosmological constant is more of a fudge factor heuristic than a part of a theory, the speed of light c may be a better candidate as a point fit. ”

    Not all calculations are curve-fits. There is not enough information there to know either way. If I have an ideal gas, then PV=nRT. If I know V & T, I can calculate P, but I have done no curve-fitting.

  113. dikranmarsupial says:

    “Dave said:

    “(2) see what sort of curve fits”

    I rest my case.”

    It is a shame when discussions end up with this sort of evasion, ignoring for a second time the key point

    The curve-fitting comment was not meant as a back-handed compliment. I was emphasising that you can’t assume it applies across all concentrations or partial pressures, and that the authors you quoted followed the process (1) make the measurements or do the MODTRAN calculations; (2) see what sort of curve fits; (3) come up with a physical rationale for why that curve fits, at least in that part of the parameter space.

    [emphasis mine]

    despite this having been drawn to PP’s attention once already.

  114. Jon Kirwan says:

    @dikranmarsupial

    I had a very similar reaction to PP’s abrupt “rest my case” quip. It’s the kind of thing that goes on when someone is being “charismatic” and using tools found in debate class to “win an argument.” And none of it has any place in a scientific discussion. Instead, points are made and countered with care from as informed and comprehensive position, as possible — to the best of their abilities. A flippant comment “sounds nice” the the lay person and feels like, “Yeah, take that!” But it’s nothing at all. It’s just being intellectually lazy and avoiding the work required of a better response.

    On the general topics of theory, experimental evidence, so called “curve-fitting,” and so on, I have only a few comments I want to add.

    If you go back to “Atmospheric Carbon Dioxide and Aerosols:Effects of Large Increases on Global Climate,” by Rasool and Schneider, published in Science, New Series, Vol. 173, No. 3992 (July 9, 1971), 138-141, you’ll find that they used a highly simplified 1D atmospheric model. Using that model, they concluded, “It is found that even an increase by a factor of 8 in the amount of CO2, which is highly unlikely in the next several thousand years, will produce an increase in the surface temperature of less than 2 K.” Specific criticisms appeared almost immediately from Charlson, Harrison, and Witt. And in 1972, Rasool and Scheider not only admitted their arguments’ weak points, but added a new, very serious defect that others hadn’t yet brought up. In 1974 and again in 1975, Schneider went on to provide refined models that reversed their earlier estimates and to show warming effects in the near-term. (Their 1971 paper also discussed aerosols, which was an important addition at the time to the discussions, although they unfortunately also used the term “ice age” in it, which became popularized in ways it should not have been.)

    My point in bring up the above is that a 1D model is simply inadequate to the discussions I’ve been seeing here. If you are attempting anything with regard to Venus or the Earth using the kind of simplifications used by Rasool & Schneider back in 1971, then you are almost certainly making a serious error merely by the fact of it. (Unless, of course, you can demonstrate that the 1D simplification, out of solid and accepted theoretical considerations, is adequate for the purposes at hand.)

    (I also know that Rasool had earlier written about Venus and the runaway greenhouse effect there a year before, in 1970. It’s likely that both have written papers on Venus, afterwards, as well.)

    Also, if you start up an Earth simulation using an arbitrary set of initial conditions, these models (if they work at all) will quickly discover the Hadley cells, for example. (About 100 yrs of simulation, often enough.) These are the kind of thing you’d expect from boundary-value problems.

    As a sidebar, there’s a book I’ve read called, “Atmospheric and Oceanic Fluid Dynamics,” by Geoffrey Vallis. It’s worth a look-see.

    In some cases, for example cloud formation, theory exists well enough to do a credible job but we don’t have the compute power for global application (last time I checked, anyway.) I’m bring up clouds because some folks like to suggest these are just “curve fits.” But cloud parameterizations aren’t just statistical curve fits and they aren’t collections of “adjustable parameters,” either. They use physically based theories, but ones targeted to describe the cloud field. By this, I mean things like fractional cloudiness or area-averaged precipitation rate, but without actually describing the individual cloud elements themselves.

    But field experiments continue in order to provide additional verification and to improve the applied techniques. An example of the impact of these experiments, which I remember from more than 10 years ago, is the boundary-layer cloud parameterization of Lock et al., circa 2000 and 2001, and tested by GCSS. Improvements for cloud parameterizations have accelerated, too, back around that time by first replacing the conventional subgrid parameterizations with more detailed high-resolution models; those capable of representing individual large clouds, at least. These ’embedded’ models include many more small-scale process interactions. One can look up “cloud-resolving convection parameterization” or just “superparameterization,” to get more information on that. But physics-based examinations to test these parameterization models are also regularly performed. MRI/JMA, I think, ran a model with 5 km gridding over a volume of some 4000km x 3000km x 22km; centered over Japan (I’m thinking here of Yoshizaki et al., 2005.) That model used a time-slice method and makes detailed projections of the evolution of small scale cloud features. This was then compared with actual obserations. Also, I remember that Sato et al., 2005, reported some encouraging results from another global cloud-resolving model. (I’ve been out of touch on this subject since then.)

    The point here is that the entire subject is complex. The comprehensive evolves almost daily, it seems, and I’d suggest that none of us here possess that view. I think PP arguing from an outsider’s perspective isn’t even worth arguing over. An arrogance of view, without first being fully informed, very likely leads to mistaken claims rather than new revelations.

    If I had a recommendation to help all of us reading this “debate,” it would be that we ask for someone who is doing active and relevant research to read the commentary here and help us with gaining a more comprehensive view about it. I suspect that the discussions here would encourage, not discourage, their input, too. Worth a try, anyway. I think we could all learn a little something from it.

    That said, I tend to feel that Dave’s perspective about “approach” is more aligned with mine, though there was a comment or two I’d probably have edited. 😉

  115. Dave_Geologist says:

    Paul, this time it really is my last word.

    (2) is not your case, it’s mine. You’re resting my case, not yours.

  116. Dave_Geologist says:

    Thanks Jon. I agree 1D models over-simplify, but they can be useful for putting across simple concepts. Of course, sometimes they may lead you astray. Another early error was putting all the CO2 in a layer at ground level, so it radiated at surface temperature and there was no greenhouse effect. I suppose that’s a 0D model. IIRC Skeptical Science and Science of Doom have pages where they go through a worked example, splitting the CO2 into multiple layers throughout the atmosphere and showing how the GHE converges asymptotically on the fully-resolved value.

    But when, as with the papers I linked to above, the 3D model shows the same behaviour as the 1D model, just with threshold values shifted, the 1D model has expository value. Especially in the hands of an author who can draw good quantitative cartoons 🙂 . Just don’t bet the planet on absolute values taken from it. In the Earth simulations I mentioned, the Hadley cells were indeed a major factor in allowing IR to radiate through spatial windows where the atmosphere was undersaturated in water vapour. You could perhaps correct for that by making the whole atmosphere a bit less undersaturated, but I suspect you’d still get the wrong answer. Just as Lewis & Curry’s 1D (global average) approach gives the wrong answer when applied to a 3D model or to a series of latitudinally segmented averages of the 3D model. Likewise, given how complex cloud/warming interactions are, correcting for clouds by simply assuming a global albedo increase has to miss out some important feedbacks.

    Even 2D models (which is what a latitudinally segmented model is) have value. My second-most-cited paper used 2D models to show that you had emergent behaviour which did not exist in 1D models of the time and whose omission had led to people reaching completely wrong conclusions about inversion events. (We’re talking 35-40 years ago so don’t even mention “3D model” 😉 – nowadays you can run much better 2D models on your phone or iPad 🙂 ).

  117. This is somewhat of a repeat of a discussion on this blog from awhile ago, trying to understand a non-heuristic physical mechanism for the logarithmic behavior

  118. dikranmarsupial says:

    PP did you read the paper?

    A few key conditions that the derivation of the ELD model relies on can be used to predict when the logarithmic relationship may not hold. These situations include the following:

    [ long list]

    which seems to support Dave’s position, not yours.

  119. https://www.theguardian.com/environment/2020/feb/06/humanity-under-threat-perfect-storm-crises-study-environment?utm_term=RWRpdG9yaWFsX0xhYk5vdGVzLTIwMDIwNw%3D%3D&utm_source=esp&utm_medium=Email&CMP=labnotes_email&utm_campaign=LabNotes

    Fiona Harvey does not mention that the long time frames involved with global warming and also appears to be less than sanguine about strong negative feedbacks kicking in and ignores the reversibility question. Harvey’s general tone is a bit less light-hearted than ATTP’s.

  120. John Hartz says:

    Mike: Thanks for flagging Fiona Harvey’s article. She is an excellent environmental journalist. Are you proposing that she and ATTP debate? 🙂

  121. John Hartz says:

    According to this Chris Mooney article, we may be witnessing a turning period in ocean currents as we speak.

    The world’s oceans are speeding up — another mega-scale consequence of climate change by Chris Mooney, Climate & Environment, Washington Post, Feb 5, 2020

  122. Yes, a critical debate/discussion with ATTP and Harvey would be great. Is it my imagination or has ATTP moved closer to luke/luckwarmer positions over the past year? I love the ideal of unicorns pooping rainbow ice cream as much as the next person, but I am dubious that my ice cream needs can be met by this method.

  123. Joshua says:

    Curious if anyone might comment on this:

    > A reading of 65 degrees was taken Thursday at Esperanza Base along Antarctica’s Trinity Peninsula, making it the ordinarily frigid continent’s highest measured temperature in history.

    The Argentine research base is on the northern tip of the Antarctic Peninsula. Randy Cerveny, who tracks extremes for the World Meteorological Organization, called Thursday’s reading a “likely record,” although the mark will still have to be officially reviewed and certified.

    The balmy reading beats out the previous record of 63.5 degrees, which occurred March 24, 2015.

    […]

    David Bromwich, a climate researcher at Ohio State University, noted, however, that while the Antarctic Peninsula has warmed strongly since the late 1940s, temperature trends in summer have been variable in recent decades, including a brief cooling spell since 1998. “So overall, this record looks to be a one time extreme event that doesn’t tell us anything about Antarctic climate change,” he wrote in an email.
    ——-

    What Bromwich said is interesting. My instinct is thst he’s right – it’s a mistake to use short term phenomena to draw conclusions about a long-term trend in a particular region. I always laugh when they post record cold recordings at WUWT.

    But it’s also hard to just dismiss record warmth recordings just 5 years apart…

    And Steig says:

    > “[This record] doesn’t come as any surprise,” wrote Eric Steig, a glaciologist studying climate change at the University of Washington. “Although there is decade-to-decade variability, the underlying trend across most of the continent is warming.”

    So? Not surprising but also not very informative? Would that be a fair (if not very satisfying) conclusion?

  124. John Hartz says:

    Mike:

    Is it my imagination or has ATTP moved closer to luke/luckwarmer positions over the past year?

    Your imagination has run amuck!

  125. John Hartz says:

    The “big picture” is sketched out in this article…To say that things are going to hell in a handbasket would be a gross understatement.

    Climate change could spark ‘global systemic crisis’, scientists warn by Laurie Goering, Thomson Reuters Foundation, Feb 7, 2020

  126. dikranmarsupial says:

    “Is it my imagination or has ATTP moved closer to luke/luckwarmer positions over the past year?

    Your imagination has run amuck!”

    AFAICS ATTP seems to go where the science leads. The science hasn’t moved any closer to luke/luckwarmer positions over the last year (hint: has the ECS plausible range shifted much in the last 30 years? No).

  127. dikranmarsupial says:

    “Yes, a critical debate/discussion with ATTP and Harvey would be great.”

    If you mean a face-to-face debate, then no that would not be great. Science abandoned that as a means of arriving at the truth a century ago (ask Darwin) because such debates are won by rhetoric rather than being right (in fact not caring whether what you say is true, but can’t be fact-checked live in the discussion, is a distinct advantage)

  128. Dave_Geologist says:

    has ATTP moved closer to luke/luckwarmer positions over the past year?

    I haven’t noticed mike. AFAICS he’s just been properly cautions about doomsaying which is not yet widely accepted in the climate-science community, just as he was properly cautions about low-ball outliers like Lewis & Curry. Consensus and all that. And of course properly dismissive of the various wackos he’s come across. OK, more generous than that or than I. He’s tried to engage and show where they’ve gone wrong, but been met by walls of wackiness or personal abuse.

  129. dikranmarsupial says:

    It isn’t actually the case that people are necessarily polarised as “skeptics” or “warmists” – but those that are will tend to view anyone that is just following the science as being one or the other anyway. This isn’t that surprising – we are all susceptible to confirmation bias.

  130. Dave_Geologist says:

    Jon, by coincidence a new Snowball Earth model is just out, looking at the impact of the location of the mountain belts formed during accretion of the supercontinent which itself made a snowball more likely. Again, showing that the detail matters when it comes to thresholds and what drives the tipping point (sea-ice growth vs. low-elevation snow vs. montane snow vs. atmospheric circulation changes). For snowball fans like me, it’s a rich source of recent references. This is one of the set which has a high-methane Palaeoproterozoic atmosphere driven by the respiration of methanogenic archaea. There is another family which uses very high CO2 to compensate for the weak Sun and has different feedbacks (weathering and erosion draws down CO2 but not CH4).

    Again the 3D models can do a lot of things a 1D model can’t, but the basic principle is the same: past a certain point, a given albedo change drives a temperature response which causes a further albedo change bigger than the original change, and you have a runaway.

  131. Dave said:

    “… but the basic principle is the same: past a certain point, a given albedo change drives a temperature response which causes a further albedo change bigger than the original change, and you have a runaway.”

    Just because it’s a positive feedback doesn’t mean it’s a runaway. That’s what I was trying to point out with my original comment concerning (Arrhenius,Clausius-Clapeyron,Boltzmann,etc)-class thermal feedbacks. “We can make the assumption that the temperature, T, reaches a steady state such that the positive feedback limits its extent as the Boltzmann factor acts as a rather weak feedback
    term. (This is not runaway warming we are talking about).”
    quoted from Pukite, et al (2019)

    So one has to first determine if albedo changes are activated WRT temperature in a similar way. It may in fact go runaway (two curves that diverge due to convexity) before hitting a rail, but it also may reach a set-point, which is essentially what regime the Earth is in after we got out of the last CO2-depleted snowball earth regime.

  132. Dave_Geologist says:

    Paul

    A given albedo change drives a temperature response which causes a further albedo change bigger than the original change, so the total change is more than twice the original change (and, unspoken, so on recursively) generates a diverging series = a runaway.

    A given albedo change drives a temperature response which causes a further albedo change smaller than the original change, so the total change is less than twice the original change (and, unspoken, so on recursively) generates a converging series ≠ a runaway.

    Check what I said. The first, not the second. I had hoped it was clear enough the first time. If not, it should be now.

  133. DM said:

    “Not all calculations are curve-fits. There is not enough information there to know either way. If I have an ideal gas, then PV=nRT. If I know V & T, I can calculate P, but I have done no curve-fitting.”

    As an example, this work we did years ago on nanostructure thermodynamics. Our group was able to show how we could monitor the layer-by-layer sublimation of atoms from a single-crystal surface with an overpressure characterized as an ideal gas — a mind-blowing experiment of measuring a ~nanogram material leaving the surface per minute. With the systematic control over the experimental parameters we did curve-fitting to show how everything was consistent with known physics. These may look like straight lines but only because they are transformed on a semi-log coordinate system.

    Van Hove, J., Pukite, P., Whaley, G., Wowchak, A. & Cohen, P. “Layer-by-layer evaporation of GaAs (001)”. Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 3, 1116 (1985). https://avs.scitation.org/doi/abs/10.1116/1.583064

    Looking back on my experimental research, I don’t think I’ve ever published something without a curve-fit of some kind — that was considered almost a standard practice. Never made sense to report on some finding unless it could be compared to some known theory or a model adapted to the experiment at hand.

  134. DM (and others say) “AFAICS ATTP seems to go where the science leads.”

    ok. I have questions.

    When ATTP says: “In the context of climate change, external factors that can lead to warming are typically called forcings. This would be things like changes to the solar flux, volcanic eruptions, and our release of greenhouse gases into the atmosphere. Feedbacks are then responses to this externally driven warming that either act to amplify, or suppress, the warming. Some of these are fast, such as water vapour and clouds, while others are slower, such as changes to vegetation or ice sheets. Some are also negative and quite strong (such as the Planck response). This means that even though the overall effect of these feedbacks is to amplify the externally-driven warming, it is limited (the negative feedbacks eventually balance the the effect of the change in forcing and the resulting positive feedbacks).”

    I think this is accurate, but also misleading because it can easily be read to mean that “the effects of forcings and feedbacks is limited.”

    When ATTP says:

    “Finally, a tipping point refers to us crossing some threshold where the climate system changes (tips), irreversibly, into a new state. There is the possibility of a global tipping point, but this is seen as very unlikely. However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice.

    If we were to cross any of these tipping threshold, then the changes would further amplify the warming (through either releasing additional CO2, or methane, or changing the albedo) and – in the case of the ice sheets – would lead to substantial sea level rise. There are a few things to bear in mind, though. The timescales are typically long; if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie; we could already have crossed some, or might not do so unless we were to warm substantially. Additionally, there is still debate as to whether or not some of these are truly irreversible; if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ”

    Again, I think it is accurate, but misleading because the framing is structured around long timescales, reversibility and has no discussion or mention of potentially catastrophic impacts that could happen well before the impacts of the tipping points have settled down into a new equilibrium state.

    as for caution, the piece suggests we use caution in how we discuss tipping points and their significance, but fails to mention or suggest caution with regard to the real world consequence of global warming that exist outside any linguistic and scientific discussion of the way we describe how global warming through use of terms like forcings, tipping points, and runaway.

    It makes me think about a scientific discussion of the the three drug cocktail that is commonly used in execution that would describe each drug carefully along with its actions, but fails to include any mention of the purpose and outcome of the drug cocktail as administered, which would be ending the life of the recipient. I think the larger framing of the discussion at least deserves an honorable mention.

    JH and others have inserted that discussion through the comments, but why would it be completely absent from the original posting? What does it mean or what does it tell us if the large, precautionary concern and frame of reference is missing from the way a scientific discussion is presented? Especially if that omission is accompanied with a focus on strong negative feedbacks, long time frames and potential reversibility? Maybe I am the only one that is bothered by this.

    No disrespect meant to anyone. Maybe I missed a sentence or paragraph or two that covers the seemingly legitimate concerns in the body of the original post that fits with the concerns raised by some folks in the comments section of this discussion?

  135. dikranmarsupial says:

    Sorry PP, your evasion of Dave’s point earlier suggests that there is no point discussing this with you any further.

  136. dikranmarsupial says:

    smallbluemike “I think this is accurate, but also misleading because it can easily be read to mean that “the effects of forcings and feedbacks is limited.”

    If you think something a physicist tells you about physics is misleading, perhaps, just perhaps it isn’t actually misleading, just that you don’t understand.

    Forcings and feedbacks are limited. There is a limit to the amount of energy that the Sun can radiate in our direction. There is a limit to the amount of CO2 that is available to be put into the atmosphere. The Planck feedback is only limited by the temperature the planet can achieve given the forcing. Venus is at an equilibriium of these forcings and feedbacks. It has experienced a runaway greenhouse effect, but it was eventually limited by the Planck feedback and the lack of any more available carbon to put in the atmosphere and has now equilibriated.

  137. at dm: I acknowledge the accuracy to the best of my knowledge. Read carefully please. The context, or lack thereof, is what I am bringing up. I think to discuss the limited nature of these things is an error if there is no mention that the limited impact of these things may be sufficient to bring about a devastating amount of human misery. In that sense, the impacts are clearly limitied and may still be clearly sufficient to create a devastating amount of misery. Am I being clear? Am I being misunderstood here or am I misunderstanding the presentation by objecting to the potentially devastating impacts which are not mentioned?

    I think this will be my last attempt to move this discussion forward on this thread.

    Cheers to all,

    Mike

  138. dikranmarsupial says:

    ” Read carefully please.”

    I did, you said something was misleading, but the “misleading” interpretation (“… it can easily be read to mean that “the effects of forcings and feedbacks is limited.”) you gave was correct. How can it then be misleading?

  139. Ken Caldeira annually asks his students – and twitter (?) – what climate science has learned in the past 20 years (+?) that is *substantively* different/not already incorporated… forcings, sensitivities, observations, mechanics, etc.

    A *very* good question.

    Amongst the only things that occurs to me (and I got a rare “twitter like”! from Ken my suggestion 👍) was indications/hypotheses of potential mechanical MICI/MISI (Marine Ice Cliff/Sheet Instability)

    A *lot* of breathless “this just in!” with respect to feedbacks, runaways, tipping points, “but teh methane!”, etc. are not new to anyone long on the science…

    I would add that the emerging ecosystem science appears most new/concerning to me. ymmv.

  140. … and for what it’s worth, I think the most recent physics on MICI/MISI suggests it might be more stable than the initial indications. Anyone up to speed? Let’s hope!

  141. … and I think that the loss of summer Arctic sea ice extent qualifies as a substantial surprise…

    But what else?

    I am by no means sanguine. I have been genuinely freaked about what we understood decades ago (and justified, as far as I can tell).

    But what’s substantially new, other than our obscene failure to reduce emissions?

  142. David B. Benson says:

    rustneversleeps — The rapidity of glacial retreat back through Icy Bay, Alaska, from the oceanside grounding line back to solid ground, suggests that the West Antarctic Ice Sheet will also quickly retreat over the portions below sea level. This is now starting at Twaites Glacier and presumably also Pine Island Glacier.

  143. David B. Benson says:

    Incidentally, Pine Island Glacier is named after Pine Island Bay which in turn is named after the Pine Island, the first ship to explore there.

  144. ok, and that’s the MICI/MISI physical mechanics… but is that (at current/updated understanding) not incorporated?

  145. David B. Benson says:

    rustneversleeps — I don’t think that anyone knows how fast it will go. The closest analogy might Meltwater Pulse 1a at the end of the glacial stade leading to the misnamed Holocene.

    https://en.m.wikipedia.org/wiki/Meltwater_pulse_1A

  146. Ok, but again, not a recent insight… incorporated as best the paleo could do…

    AIUI, hypotheticals on MICI/MISI mechanics are an attempt to close that (amongst other) very “discrepancy” – and, indeed, in the last (15-ish?) years, we have gained *some* insight… and lost some elsewhere…

    I am still curious about substantial processes that were not understood/incorporated in IPCC AR5 WG 1.

  147. David B. Benson says:

    rustneversleeps — There is a recent report about the miniature submarine which explored a bit of the underside of Thwaites Glacier to discover something about the melting along the seafloor. I am uncertain about whether this changed any current hypotheses.

  148. David B. Benson says:

    https://en.m.wikipedia.org/wiki/Thwaites_Glacier
    mentions the recent research results.

  149. JCH says:

    Melting slowly in place/calving in place is not really the same thing. Collapse is about a major advancement. The Roman Colosseum has been falling down since the day it was built. If you wake up tomorrow to news that it suddenly became a pile of rubble overnight, that’s what they’re after with MISI/MICI. Ice sheets and ice cliffs are structures, so the physics of how/if materials fail is being applied to them. I think the first efforts in model them in that manner actually started over 20 years ago. Before Hansen, I don’t think people were at all concerned with it. How many times have it been written it will take thousands of years to melt them. Greenland is an ice fortress. I read that.

  150. Jon Kirwan says:

    @Dave_Geologist

    Thanks for the open access link. I’ll take some time to read it. I haven’t spent much time on “snow ball” Earth, but I should. I did spent quite a lot of time on trying to simulate Earth’s atmosphere (hundreds of stacked-up slab models in simplified form) to see if I could work out if the Earth even remotely could become a “Venus” result. My simplistic results (and they cannot be trusted, I assure you) were that the sun itself would need to increase its insolation by about 5% before it would even be possible. (I included H20 and CO2, but little else to be honest.) I did tap into MODTRAN and HITRAN. But the bottom line is that I found from a relatively simplistic model that we just can’t get to a Venus situation without more insolation.

    As a sidebar, and I’m not sure it’s been mentioned here, but the Bond albedo of Venus is such that it actually absorbs slightly LESS insolation from the sun as does Earth. Venus reflects quite a lot of its insolation. Yet it is VERY HOT on the surface. It was a surprising “trivia detail” that I learned many years ago. People often imagine that Venus is closer to the sun (it is) and therefore that is all that is needed to understand why it is so hot. But they don’t often know that Venus reflects away more than twice the insolation it receives, such that it “keeps” less than the Earth does.

    I considered the idea of trying to work out Venus using my simplified model. But it really wasn’t as easy as I’d earlier imagined. So I dropped the idea.

    The recent paper you provided is very interesting, so I will read it when I get a moment.

    [By the way, I’ve begun to have a renewed interest in geology. Some of the recent discussions about the pair of “blobs” within Earth’s mantle and some papers I’ve seen with respect to the Hawaiian-Emperor bend and the differences in minerals found over time. (A recent idea suggests that a plume “got stuck” against one of the blobs, to create that kink, and began to erode some of the material from that blob to mix with its own materials. This makes me all the more curious about the blobs themselves and what they may be. There is a suggestion they are related to the impact that created the moon, even!) I’m also just interested in Oregon geology, in general, because I live here. I’m hoping to take one of my sons around the place to look at varying formations and to think about what they may or may not imply. I’m envious of what I perceive the light of your experiences might shed. Oh, well. Life is all too short, I suppose.]

  151. David B. Benson says:

    Jon Kirwan — I recommend taking along a copy of “Roadside Guide to Oregon Geology” as you tour the state.

  152. Dave_Geologist says:

    Jon, the 1D models suggest we can get to a runaway by adding CO2 at our current insolation (but not from CO2 alone – you have to boil the oceans and it’s water vapour which drives the runaway). Perhaps not, because the 3D models have a higher insolation threshold, but I would have thought you could do it with an arbitrarily high CO2 partial pressure – say 1 bar. 30,000 ppm is enough in the 1D models. It’s not a meaningful path for AGW to take us down because even if there was enough accessible fossil carbon, we’d all have died of asphyxiation and heatstroke long before we’d burned it all.

    On the blobs, there are some suggestions of heterogeneity dating back to the early mantle. Not sure about the moon-forming impact though – everything should have been well-mixed and melted. A hot-spot sceptic, Gill Foulger, cited Iceland as a non-plume because the basalts have the geochemical signature of mantle fertilised by subducted crust. Trouble with the non-plume arguments is that absence of evidence is not evidence of absence, and as seismic has got better plume after plume has been imaged. Including Iceland. There is a rather neat explanation for Iceland, that it’s both. In a hot-spot frame it can be matched to the Siberian Traps plume, which even if still active should have lost all its readily melted material in the process of making the biggest Phanerozoic Large Igneous Province. Which is supported by the fact that it didn’t leave a subsequent hot-spot trail. It ran out of fuel. Just as well or we might not be here to discuss it. The Great Dying might have been an Even Greater Dying. The suggestion is that it was reactivated (refueled 🙂 ) when it met up with subducted oceanic crust dating back to closure of the Iapetus (proto-Atlantic) Ocean.

  153. David B. Benson says:

    Regarding Venus,
    https://en.m.wikipedia.org/wiki/Atmosphere_of_Venus
    it is not quite in equilibrium because the sulfuric acid at the top of the atmosphere is losing water, becoming just hydrogen sulfide. So the albedo is slowly changing.

  154. David B. Benson says:

    Oh dear. I meant to write
    Becoming sulfur dioxide.

  155. David B. Benson says:

    No, no, no.
    Sulfur trioxide!

  156. Jon Kirwan says:

    @David B. Benson

    I have both the original (1978?) and the newer (2014?) editions of that book.

  157. Jon Kirwan says:

    @Dave_Geologist

    This is the recent article I saw on the “blobs”:

    https://www.quantamagazine.org/continents-of-the-underworld-come-into-focus-20200107/

    Inspired some curiosity, if nothing else.

    Regarding the models I played with, I did completely boil the oceans away in the runs. I still couldn’t get a runaway Venus here. Not without more insolation. But again, my modeling was naive. It was just a proof of concept for some other questions I had, and I decided to “push it” to see what it said about the required insolation assuming the oceans were boiled into the atmosphere. But I had exactly zero chemistry in the model — I didn’t have any way of figuring out what might really happen with sulfur and H20 (sulfuric acid) or any other chemistry that almost certainly would occur. So as I said, it’s just a very cheap guess about things. But it was interesting to me that it required more insolation than we actually have right now. Not by much. But some. What made brought this to memory, today, was that some years later I found a peer-reviewed paper on the topic using GCMs and it had a similar answer — we need more insolation than we have, right now. So I thought, “Oh, so maybe a simplified approach isn’t all that terrible at making back of the envelope calcs.” But it is probably more coincidence than anything. I’m sure the paper did a comprehensive job and all I had was an accidental coincidence.

    Of course, we will be getting more insolation as the sun ages. So that’s ahead, regardless. But I won’t be around for that. 🙂

  158. angech says:

    I understand protecting people’s sensitivities so fair enough.
    Can I just post that I agree with DM’ s comment
    “Forcings and feedbacks are limited.” Wholeheartedly?
    Thanks.
    This is why Dave’s comment
    “A given albedo change drives a temperature response which causes a further albedo change bigger than the original change, so the total change is more than twice the original change (and, unspoken, so on recursively) generates a diverging series = a runaway.”
    Is problematical.
    We can structure scenarios to give possibilities of change but they are like the road runner magically finding extra energy.
    Potential energy scenarios lurk in many places. Like puffing into the sails to make you go faster. Like ice cliffs falling. Like doggerbank collapsing or the Mediterranean opening up.

    But when we come to physics energy in is energy out and generally there is a limit, not a runaway, for obvious reasons.

  159. Dave_Geologist says:

    If you haven’t seen it already, Jon, here is a review paper about the blobs (LLSVPs). Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle. It includes a third possibility, not really mentioned from a skim of the Quanta article, that you get a pile-up of downgoing subducted slabs underneath a rising mega-cell. The subducted material is both denser and lower-melting than the surrounding mantle, so there’s a narrow line between it staying buried and solid or partially melting and contributing to low shear velocity and to plumes.

    One way of getting high 3He/4He ratios is to sample primitive mantle which has little 4He. Another is by partial melting at mid-ocean ridges which extracts all the U and Th from the mantle source so that accumulation of 4He in the melt residue is restricted and the original high 3He/4He maintained. Hence the interest in subducted slabs of old oceanic lithosphere. Of course you can go chicken-and-eggy and say that the anomalies, whatever they are, are primitive but they have controlled the spatial distribution of large-scale convection, and that the pile-up of old slabs is against a pre-existing controlling feature.

  160. Dave_Geologist says:

    It’s the Sun angech. The energy of the Sun-Earth system remains the same. For a period of time following a forcing such as a CO2 increase the Earth retains more of the Sun’s incoming energy than it radiates. It warms up until the level at which the atmosphere radiates gets hot enough to once again balance the Sun’s input. Then there is a new equilibrium.

    It is possible for a steam atmosphere to have a runaway in that part of the parameter space where the energy radiated gets decoupled from the surface temperature and stays constant for a large increment of surface heating. Within that interval the surface continues to warm, even with no further external forcing. Eventually it gets hot enough to radiate in the near infrared, the runaway ends and we return to business-as-usual. Just much, much hotter. Like a super-Venus. I did say above that it only applied in a limited parameter space.

    The same for the Snowball transition. The albedo from the extra snow or ice reflects enough sunlight that the upper atmosphere is radiating more energy than is arriving from the Sun (or rather arriving and being absorbed by the surface). Normally the atmosphere would cool, with a lag, bringing energy-in and energy-out back in balance. But for certain conditions, in the tropics, it can cool the surface enough to freeze more ice than the area of the original “extra snow or ice”. The process becomes self-sustaining within a certain parameter space: a runaway, until there’s no more water to freeze. Then the runaway ends (or, in some models, it ends where a patch of residual ocean doesn’t freeze so easily, perhaps because of changed ocean currents due to the extensive sea-ice cover).

    All conservation laws are honoured. And no-one said the runaway lasts forever. In fact I specifically said it didn’t.

  161. JCH says: “How many times have it been written it will take thousands of years to melt them. Greenland is an ice fortress. I read that.”

    I think that is the point that ATTP made with mention of the long time frames involved in these changes. It is certainly accurate to state that it will take centuries, or even thousands of years, for the full effect to manifest. Thanks to angech and JCH for weighing in with their support on this matter.

    Interesting info on the non-equilibrium and sulfur something status on Venue. I am picking up lots of useful information this week.

    Cheers

    Mike

  162. dikran asked “you said something was misleading, but the “misleading” interpretation (“… it can easily be read to mean that “the effects of forcings and feedbacks is limited.”) you gave was correct. How can it then be misleading?”

    I think it is easier if I give you examples of things that may be
    true and also misleading:

    Crime pays.

    “If you commit a horrible crime, the government will give you free food and accommodation, sometimes for the rest of your life.” – koalameat

    Water babies

    “If a human baby is born underwater, it can live its entire lifetime submerged, without ever surfacing for air.” – Scrappy_Larue

    Fallopian Tubes.

    “On average a person has approximately one fallopian tube” – 3BallJosh

    The healing power of the Walkman

    “Smallpox was eradicated within a year of the release of the original Sony Walkman.” – GhostoftheWolfswood

    The deadliest substance

    “Every single person who drank water in the 1800s died.” – VictorBlimpmuscle

    sourced from reddit

    I think it is simply true that statements can be true and misleading. Do you accept that this is true, Dikran?

    Respectfully,

    Mike

  163. dikranmarsupial says:

    Mike, sorry, I have no time for evasion, if you say people are being misleading don’t expect a friendly reception if it turns out the the misleading message you perceived was correct. Not being able to accept you are wrong doesn’t help.

    Angech as I said, you can have a runaway, it just doesn’t run away to infinity. It runs away to a climate like that of Venus.

  164. Dave_Geologist says:

    Jon, in your model did you have a dry or a moist stratosphere? The threshold is lower for a cold trap and dry stratosphere: Fig. 1 of The runaway greenhouse: implications for future climate change, geoengineering and planetary atmospheres. The 3D model in Increased insolation threshold for runaway greenhouse processes on Earth-like planets doesn’t say you can’t get a runaway if you dramatically increase CO2 because it keeps present-day CO2. But presumably you’d need much more than Goldblatt’s 30,000 ppm, so we’d be even deader when we triggered the runaway in a 3D model. I’ve been reading the papers again and there are some apples and oranges. Goldblatt uses outgoing TOA flux (so, when we’re in balance, what is absorbed by the surface after albedo effects etc.), about 240 W/m2 today, whereas Leconte uses incoming solar irradiance of about 340 W/m2. That’s why the 3D threshold is so close to our current orbit (0.95 A.U. and 375 W/m2). I think when ATTP commented upthread about how different they were it was that apples-to-oranges comparison. And with our present CO2 level, Goldblatt’s model has overshoot before the runaway (curve 2 in Fig 5), so the runaway threshold is about 320 W/m2 TOA flux and about 50°C surface temperature, not the asymptotic 290 W/m2 TOA flux. So we’re probably just talking about the difference between 0.95 A.U. and 0.97 A.U. for 3D vs. 1D models.

  165. Dave said:

    “The same for the Snowball transition. The albedo from the extra snow or ice reflects enough sunlight that the upper atmosphere is radiating more energy than is arriving from the Sun (or rather arriving and being absorbed by the surface). Normally the atmosphere would cool, with a lag, bringing energy-in and energy-out back in balance. But for certain conditions, in the tropics, it can cool the surface enough to freeze more ice than the area of the original “extra snow or ice”. The process becomes self-sustaining within a certain parameter space: a runaway, until there’s no more water to freeze. Then the runaway ends (or, in some models, it ends where a patch of residual ocean doesn’t freeze so easily, perhaps because of changed ocean currents due to the extensive sea-ice cover). “

    The conventional explanation of the snowball earth transition I thought was the article by Lacis, Schmidt, Rind, and Ruedy “Atmospheric CO2: Principal Control Knob Governing Earth’s Temperature” in Science (2010).

    “If the global atmospheric temperatures were to fall to as low as T_S =T_E, the Clausius-Clapeyron relation would imply that the sustainable amount of atmospheric water vapor would become less than 10% of the current atmospheric value. This would result in (radiative) forcing reduced by ~30 W/m^2, causing much of the remaining water vapor to precipitate, thus enhancing the snow/ice albedo to further diminish the absorbed solar radiation. Such a condition would inevitably lead to runaway glaciation, producing an ice ball Earth.”

    This is essentially the physical basis that I used in solving for the 2 stable set-points (T_S=nominal, T_E=effective) as mentioned in my first comment on this thread. I applied the continuous Clausius-Clapeyron T dependence by itself to arrive at the quadratic formula solution, but it’s feasible to also include some type of positive albedo feedback to the formulation. Whatever the albedo feedback value is, it would modify these set-points, and if it happened to be stronger than a T dependence, it would add another order to the quadratic equation, making it a cubic equation with 3 set-points. If the albedo term is only a slight perturbation, the 3rd set-point would be much higher than T_E, but if it is too large then its impact would be to increase T_E while lowering the 3rd set-point value.

    This would be a rationale for suggesting a large uncertainty to the equilibrium climate sensitivity, as the positive feedback albedo factor is mathematically forcing the log(C) term to become less convex with respect to T and thus elevating the effective T_E set-point.

  166. angech says:

    SMB
    “Again, I think it is accurate, but misleading because the framing is structured around long timescales, reversibility and has no discussion or mention of potentially catastrophic impacts that could happen well before the impacts of the tipping points have settled down into a new equilibrium state.”
    I misinterpreted this bit too when I read you. English is a …… (difficult language at time to get one’s meaning across in)
    “Misses out on the dangers of” would have been a better choice perhaps.
    Thanks for your refreshing set of quotes and views.
    Took me a while to get the baby one as I am a bit too literal most of the time.

  167. David B. Benson says:

    Further ecosystem collapse:
    https://m.phys.org/news/2020-02-el-nino-contributes-insect-collapse.html

    Tipping over still further…

  168. Dave_Geologist says:

    Paul, that’s mostly another way of saying the same thing, but probably less intuitively for angech and in a 1D model like Goldblatt’s for the Venus runaway. Where, to coin a phrase, climate sensitivity goes “to Infinity and beyond!”.

    If that was all there was to it, why do 3D models consistently flip when ice gets past the tropics? Why do some 3D models remain ice-free in mid-ocean? Why does the presence, absence, location and trend (N-S or E-W) of mountains matter? Why does having or not having a supercontinent matter? What happens if it snows on liquid oceans which cover half the planet? What is the partial pressure of H2O above those oceans compared to a continental interior undersaturated in H2O and at -60°C? How do you average that over the globe? Etc.

  169. David B. Benson says:

    Dave_Geologist, keep it up about Snowball Earth. I find it helps about our current predicament.

  170. John Hartz says:

    Two more articles directly related to the OP…

    Worst Case Climate Change Scenario Is Scary, But The Reality Could Be Even Worse by Steve Hanley, CleanTechnica, Feb 5, 2020

    The Worst Climate Scenarios May No Longer Be the Most Likely by Chelsea Harvey, E&E News/Scientific American, Jan 30, 2020

  171. attp says “There is the possibility of a global tipping point, but this is seen as very unlikely. ”

    Are tipping points very unlikely? I googled that and find the following article that I think is pretty mainstream on that question:

    https://www.nature.com/articles/d41586-019-03595-0

    Nov 27, 2019 (pretty current)

    headline: Climate tipping points — too risky to bet against

    Sub-headline: The growing threat of abrupt and irreversible climate changes must compel political and economic action on emissions.

    authors:
    Timothy M. Lenton,
    Johan Rockström,
    Owen Gaffney,
    Stefan Rahmstorf,
    Katherine Richardson,
    Will Steffen &
    Hans Joachim Schellnhuber

    from that article: “Politicians, economists and even some natural scientists have tended to assume that tipping points1 in the Earth system — such as the loss of the Amazon rainforest or the West Antarctic ice sheet — are of low probability and little understood. Yet evidence is mounting that these events could be more likely than was thought, have high impacts and are interconnected across different biophysical systems, potentially committing the world to long-term irreversible changes.”

    Do others read this article in Nature and this blog post and find them to send a distinctly different message to the reader? What are the major difference that anyone notices, if any?

  172. smb,

    Maybe read the part directly after the sentence you pulled from ATTP’s post about *a* “global” tipping point?

    However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice.

  173. small,
    Yes, I’ve read that. Carbon Brief also had a very nice article about tipping points today.

  174. John Hartz says:

    ATTP: I intended to flag the Carbon Brief article but you beat me to it. Perhaps you should use it as a springboard for a new OP.

  175. smb,

    Maybe read the part directly after the sentence you pulled from ATTP’s post about *a* “global” tipping point?

    However, it is possible that we could cross thresholds where some parts of the system undergo essentially irreversible changes. Examples would be melting of the West Antarctic Ice Sheet, the Greenland Ice Sheet, Amazon rain forest die-off, release of carbon from the permafrost, and the disappearance of summer Arctic sea ice:

    Yes, and I read the sentences after that one:

    ” There are a few things to bear in mind, though. The timescales are typically long; if we cross a tipping threshold it will still take a long time (centuries) for the full effect to manifest. Also, we don’t have a particularly good idea of where these thresholds might lie; we could already have crossed some, or might not do so unless we were to warm substantially. Additionally, there is still debate as to whether or not some of these are truly irreversible; if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ”

    I do not pick up any sense of urgency or significant concern from the ATTP post about tipping points, where I certainly get a sense of urgency and significant concern when I read the Nature or Carbon Brief pieces.

    When ATTP says, “if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ” I would be inclined to think the answer is maybe some would reverse, but I would then ask: How and when do you think we will be able to artificially draw down atmospheric CO2? This looks very much like a magic wand solution to me. This looks like a technocrat’s solution that is roughly equivalent in detail and likelihood to the theocrat’s solution that suggests An All Powerful Being Who Loves Us may rescue us if we are faithful and fill the coffers. I love pie, pie in the sky not-so-much.

  176. John Hartz says:

    Mike: I have to admit that I find it hard to decipher the text (all or portions thereof) of many of your posts. You do, however, have a bent for taking contrarian positions for the sake of being contrarian rather than for being objective.

  177. Joshua says:

    Sbm –

    I’m going to take the liberty to suggest a slight edit to the section of Anders’ post that you excerpted (indicated by bold) to see if it shifts you reaction

    > EVEN if we could artificially draw down atmospheric CO2 would some, like Arctic summer sea ice, then reverse? ”

  178. At JH: sorry to hear you find it hard to decipher my posts. My take on thing tends to match well with folks like you, DBB, VTG and a few others who seem quite alarmed.

    I sometimes tire of pushing the alarm button and switch to cheerleader for the status quo mode in an attempt to see if it is possible to push the folks who appear to not be alarmed to express some/any sense of alarm. It’s probably a waste of time and maybe just creates confusion.

    Does that help?

    Tthink how much happier we might be if we were big fans of Trump and it also turned out that global warming and the sixth extinction are a hoax. Wouldn’t that be a happy situation to be in?

    I can’t get there from here. Bummer

  179. yes, your edit helps a little. But rather than slide in “even” in that sentence, I think it would be better to leave that sentence alone and add a sentence after that says, Of course, the problem with hypothetical reversals that might happen with a draw down of atmospheric CO2 is that there is nothing planned along on those lines that we can scale up quickly, so this technological solution is really a spherical cow. It simply doesn’t exist in nature at this time.

  180. smb,

    It simply doesn’t exist in nature at this time.

    Actually, as ATTP has patiently explained over several years here, it does indeed exist in nature. Add in reforestation/afforestation at scale, and we could make a serious dent in atmospheric CO₂ on decadal to century scale. And temperatures would fall

    That’s not the question. It is more whether “systems” would respond. For instance, as we melt the ice sheets, we are reducing their elevation. So it is not clear that returning to the the GMST at which we melted would be be sufficient to halt or reverse further melting. Etc.

  181. David B. Benson says:

    smallbluemike, ,one means of lowering the carbon dioxide concentration of the atmosphere is via planting trees:
    http://bravenewclimate.proboards.com/thread/694/trillions-trees
    Of course emissions must cease.

  182. for those of you thinking planting trees is the solution:

    https://climate.nasa.gov/news/2927/examining-the-viability-of-planting-trees-to-help-mitigate-climate-change/

    does it pencil out? Remember, I said solutions that am talking about solutions that we can deploy and that pencil out:

    the math turned out to be a little shady. Last month a bunch of climate scientists and ecologists piled onto that tree research in the same journal, calling out numerous errors in the first team’s calculations.
    https://www.wired.com/story/trees-regenerative-agriculture-climate-change/

    But, again, did ATTP mention how he thought this was supposed to happen in the real world or is it just pie-in-the-sky?

    Absent a real plan about how this might happen, it looks wrong to me to suggest it will or could happen.

  183. … just to be clear, my screenshots above are (per the links) plots from Hansen et al, and Archer et al.

    Don’t assume re/afforestation…

  184. smb, my most recent post was made before I realized you had made another comment…

    Maybe just me, but you seem to persist here with variations of “but you have somehow overlooked *THIS*!!!”

    my two links above were to papers by lead authors James Hansen, and David Archer…

    … our “host” here is Ken Rice…

    Maybe entire discussions like “but tipping points!” is more nuanced, science-based than “but trees!”, etc.?

  185. At RNS: I try to be generally ok with a wait and see approach. Let’s go down the road a year, maybe two at the outside, and see if the tone here has changed. People used to bash Guy McPherson pretty hard and pretty regularly, but that doesn’t happen as much as it did a couple years ago.

    Your graphs are impressive, but I don’t know what to make of them. I keep looking at this one:

    https://www.google.com/url?sa=i&url=https%3A%2F%2Fcleanet.org%2Fdetails%2Fimages%2F87131.html&psig=AOvVaw29q8VXxYIoLHcBlrGGS9wk&ust=1581474938176000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCNDRm7G7yOcCFQAAAAAdAAAAABAD

    If there are things that we can easily do at scale that create changes in this graph, why aren’t we doing them? Can we really do them? Will we really do them? When will we do them?

    It’s been a long day. I have been texting for Bernie today and dealing with a lot of pretty crazy Trumper responses, so I am tired and may not be thinking as clearly as I would like.

    Cheers,

    Mike

  186. David B. Benson says:

    Half-a-million insect species face extinction:
    http://bravenewclimate.proboards.com/thread/159/climate-change-emergency?page=4#post-6241
    provides the full citation.

  187. David B. Benson says:

    smallbluemike, it appears that all the points raised by Saatchi, in the NASA article that you linked, and many more, have been considered in the articles linked in the BNC Discussion Forum thread which I linked here for you.

    It is past time to begin reforestation, afforestation, and other plantings around the world. All without understanding of the ‘final’ consequences, centuries hence.

  188. An interesting point to consider is the distinction between (1) runaway warming to an extreme greenhouse and (2) runaway cooling to a snowball earth.

    With the Lacis et al set-point model of a catalyzed H2O warming w/ CO2 activation, the runaway lasts until it reaches either of the two set-points of snowball earth (a runaway cooling) and current CO2 concentration (a runaway warming). These are the limiting “rails” of the positive feedback process.

    This process can be used to understand past glaciation cycles with a Milankovitch orbital forcing pushing the steady-state conditions in one direction or the other.

    I think the question now — with the significant man-made CO2 activation added to the loop — is whether additional warming feedbacks will arise, and whether they will create a new set-point that the earth will reach that isn’t predicted by the log(CO2) w/uncertainty that is the consensus thinking. The fat-tails in the uncertainty is where all the concern is and this is where someone like Curry’s uncertainty monster needs to focus on.

  189. ATTP: do you have any interest in revisiting your post about the Wicked Problem from January 3, 2018? Maybe a review of what you thought at that time about this problem and if any of your thoughts on the problem have changed since January 2018. Secondarily, maybe look at your “action plan” for the problem, wicked or not, and provide an update on how the species has done over the past two years.

    Cheers,

    Mike

  190. Dave_Geologist says:

    Paul, I suppose some reassurance against fat-tail Venus-style runaways is that if you invoke natural tipping points (tundra, hydrates etc.), these are things which could have occurred in the past when the climate was much hotter than today (by 10°C or more) and didn’t, with insolation much like today’s. Of course that may mean there’s only one chamber loaded in the Russian-Roulette gun. And if you do it by burning fossil fuel we’ll have made the world uninhabitable and stopped burning fossil fuel before we reach the runaway temperature. Long before, probably. IIRC the early Triassic was no more than 10-12°C warmer than today and the tropics were uninhabitable by reptiles or fish, let alone mammals or humans in megacities. I don’t think we could get past that point without a global, probably nuclear, war or three which should nicely trim back our emissions once the fires have gone out.

    And there’s direct geochemical and indirect genetic evidence that the Archaean oceans were hot (60-80°C) and covered most of the globe, with less continental crust and most of that forming shallow seas rather than land-masses. With the dim young Sun there must have been high concentrations of CO2 (no continental weathering to speak of so little drawdown) and CH4 (produced by methanogenic archaea, and not oxidised because no photosynthesis and no oxygen). The methane would have been limited by photolytic breakdown in the upper atmosphere and escape of hydrogen to space (no ozone layer either), and the CO2 by slower sea-floor rock weathering. That must be as close as we came to boiling the oceans and we didn’t.

    AFAIK most or all of the runaway calculations either directly do a line-by-line analysis rather than making a logarithmic assumption, or do a line-by-line analysis and curve-fit, discarding the logarithmic approximation where it no longer works. That’s implicit in all the steam atmosphere ones, because otherwise you could not get to a point where TOA emissions saturate at a constant value, independent of surface temperature.

  191. At DG: I find “runaway (to Venus)” to be a distracting canard because it is can create so much confusion and disagreement. Apparently, the term “runaway” has been defined as the condition where water is no longer present at planetary surface. I can accept that definition, but I think it’s not very useful because it is so unlikely and largely irrelevant to our species’ plans for emissions. The runaway to Venus definition is also a bit a shame because the word could also be used to describe the change in temp that occurs as tipping points from planetary conditions from on equilibrium state to the next equilibrium state. I find that definition to be more useful than limiting runaway to mean only the temp increase that would cause there to be no more water on the surface.

    I think many alarmed folks use runaway in the second sense. So, as we pass a tipping point that will move us from one equilibrium state to the next one, we might be talking about a “runaway” temp increase of 2 or 3 degrees C (on top of the 1 degree plus that we have already provided). A couple degrees is certainly not going to boil off all the water at the surface, but a couple small runaways of this type or a large one that brings an equilibrium with 5 to 8 degrees of new temp will be sufficient to undo our species and many others. As has been stated above, a temp increase of 2 to 4 degrees is not ideal, it’s not a walk in the woods.

    I think I will try to remember to use tipping period from here on out to describe the time period between equilibrium states to avoid these definitional problems. The term tipping period would then be described by the time passage and temp increase between equilibrium states.

    In your comment above you say:

    “I suppose some reassurance against fat-tail Venus-style runaways is that if you invoke natural tipping points (tundra, hydrates etc.), these are things which could have occurred in the past when the climate was much hotter than today (by 10°C or more) and didn’t, with insolation much like today’s.”

    Could you expand your thoughts a bit on this statement? I just want to be sure that we are in agreement that natural tipping points (tundra, hydrates etc.) were passed and completed (melting, etc) in the temp range that you chose. I also want to be sure that we are in agreement that a climate 10 degrees hotter than today is a climate where human civilization (perhaps all human being) no longer exist.

    Beyond that, if you could switch from a reassurance mode about the unlikelihood of runaway to Venus to the explicit dangers of specific tipping periods with their temp and time constraints on occasion, I would appreciate it. Any chance of that? Is it a reasonable request?

    Cheers,

    Mike

  192. smallbluemike, It’s interesting to consider that the climate sensitivity of CO2 alone is 1.2C per doubling (i.e. logarithmic) but the fact that the positive feedback of H2O along with its own logarithmic dependence pushes the effective climate sensitivity up to 3C per doubling. If there are other Arrhenius activated sources that can compete with H2O such as hydrates and permafrost sources, these will also add to the effective doubling. If these aren’t tipping points per se at least they will work to incrementally reposition the Lacis non-snowball climate set-point upwards in temperature.

    Apparently for the recent models that are “running hot”, the incremental upward repositioning of effective climate sensitivity may be mainly due to the distinction between water vapor and water vapor in the form of clouds, especially in the southern hemisphere. From “Causes of Higher Climate Sensitivity in CMIP6 Models” :

    “Here we find that the temperature response to an abrupt quadrupling of atmospheric carbon dioxide has increased substantially in the latest generation of global climate models. This is primarily because low cloud water content and coverage decrease more strongly with global warming, causing enhanced planetary absorption of sunlight—an amplifying feedback that ultimately results in more warming”

    However, Zeke Hausfather says the “running hot” may not be a universal result, as this is just an observation based on a subset of the reported results. Many are still not running hot.

  193. Dave_Geologist says:

    mike, I didn’t mean that those tipping points did’t happen. There were indeed events with large releases of non-volcanic fossil carbon. Those are what we have to be concerned about. A 10°C rise would destroy civilisation. 30-40°C would wipe out most advanced life. I meant that those events did not drive us into a Venus runaway.

  194. Dave_Geologist says:

    mike, I would probably define runaway as a bifurcation between two stable states, with no stable state between. Snowball Earth as well as Venus. Based on the 1D models, and the observation that 3D models have higher insolation thresholds than similar 1D models, through things we know are real and missing from 1D models like the Hadley Cells, I would see the only way for Earth to undergo a Venus runaway would be if it was triggered by CO2 or CH4 emissions. Based on Fig. 5 of Goldblatt’s RSTB paper, in scenario 2 runaway doesn’t start where the oceans boil. It starts at a GMST of about 50°C where you pass the hump and TOA emission decreases with increasing temperature. Ocean boiling is a consequence of (for that curve) insolation-driven CO2-controlled runaway. For curve 3 it’s more gradual, but again you can’t have a steam atmosphere until you boil the oceans, and you need CO2/CH4/etc. or increased insolation to boil the oceans. (Note that these are insolation-driven curves at constant CO2; I’m using them as an analogue.)

    The distinction between that and other tipping points like hydrate or tundra release are that those are forcings not feedbacks: the runaway is a change in the feedback with no additional forcing. With those forcings the climate sensitivity stays the same (ECS, at least). Although you could argue that they are akin to Earth System Sensitivity or ESS, just happening now and not in a thousand tears time. In a runaway climate sensitivity becomes infinite or undefined (over a certain temperature range, until you reach the second stable equilibrium where you can emit in the near-IR or there’s no more ocean to freeze).

    The runaways have tipping points, but not all tipping points are runaways. That may be overly technical for most people, but you’ll notice that the scientific papers use tipping point for the tundra etc. and runaway only for runaways as I’ve defined it.

  195. Dave_Geologist says:

    Coincidentally, another tipping point was just published:

    Crossing thresholds on the way to ecosystem shifts (commentary)

    Global ecosystem thresholds driven by aridity (paper)

    Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.

  196. Thanks DG. I am trying to wrap my head around this. It is pretty technical. I will attempt to adjust my thinking and refer to tipping points or tipping periods and avoid the term runaway. I don’t think I can live long enough for a runaway to be clearly identified as underway, so it’s kinda academic anyway.

  197. Philip S. Webster says:

    This is a fantastic blog with some really great posts many too technical for me but converting to Tipping Period is a good idea.

    BTW: noting the 65 degrees way down South as you all probably know it made it to 70 degrees a week later.

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