Hawking is wrong

I guess the big alarmist news at the moment is that Stephen Hawking has been quoted as saying:

Trump’s action could push the Earth over the brink, to become like Venus, with a temperature of two hundred and fifty degrees, and raining sulphuric acid.

Well, this is simply not true. As this Climate Feedback says:

It is not possible for Earth’s climate to become as extreme as Venus’ climate in the foreseeable future. And even extreme global warming would not be linked to sulfuric acid precipitation, which occurs on Venus because of volcanic emissions of sulfur gas.

As Chris Colose mentions in the Climate Feedback article, it is theoretically possible to make modern Earth hot enough such that the upper atmosphere becomes quite wet and conducive to substantial water loss to space. However, even this would not be a Venus-like runaway and it is also extremely unlikely (probably, virtually impossible).

On Twitter, Robert Grumbine made the point that a Venus-like runaway is far less likely than something like an extinction-level asteroid strike, and we don’t exactly go around worrying about something like that (we do, however, commit some resources to keeping track of asteroids).

As Ken Caldeira also pointed out, unrestrained fossil fuel burning likely leads to nasty climates, but not as nasty as Venus. I think this is a key point; we don’t need to invoke extremely unlikely (virtually impossible) catastrophic scenarios in order to argue that continuing to pump CO2 into the atmosphere might be a really bad idea.

So, one of the obvious problems with what Hawking has said is that it is simply wrong. The other is that this is an important issue and we really should be discussing the real consequences of continuing to emit CO2 into the atmosphere, not having to deal with high-profile people making alarmist claims. Of course, in the grand scheme of things, this is probably just another blip along the ever complicated climate communication highway, but it would be nice if people who should know better didn’t keep scoring these kind of own goals.

Links:
Stoat on Hawking radiation.

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64 Responses to Hawking is wrong

  1. Magma says:

    From an Earth geologist’s point of view, Venus is right up there with Mars as the second most interesting object in the solar system. Too bad its 90 atmosphere, 460 °C surface is so much more hostile to probes than that of Mars, and its Earth-size gravity well and thick atmosphere so prohibitive of returning surface samples.

    A close sister of Earth, what happened to its water budget? How much was lost to space via UV photodissociation, how much is locked in its mantle, how much simply never accreted? Why is its magnetic field so weak, when it should have a liquid outer metallic core? Did it ever experience plate tectonics similar to Earth? When did volcanism cease (or has it)? What type of volcanic rocks were erupted, and how does Venusian bulk rock and isotopic chemistry differ from Earth’s?

    The lack of water can potentially explain the lack of Earth-style tectonic activity on Venus, and even the CO2 rich atmosphere, since almost all of Earth’s carbonate budget is cycled through the oceans via low temperature surface weathering of silicates followed by organic-mediated precipitation processes, then cycled through the crust and upper mantle afterwards.

    But that said, thermal runaway and a Venus-style fate is highly unlikely for Earth, at least not for several billion years.

  2. Barry Woods says:

    The runaway Venus thing isn’t new claim, seen on occasion in the last ten years. I guess Hawking’s saying it got a lot more attention. I note Prof Richard Bette volunteered to have a chat if somebody could put him in touch.

  3. Barry,
    Yes, it’s not new, but it’s not common. It’s also not as if it doesn’t get pretty quickly refuted.

  4. Barry Woods says:

    Possibly quite widely read though over the years and the refutations not noticed by the public (or Professor Hawkings! 😉 ) Usually variations of “runaway climate change” and “become like Venus”..

    It is a shame Hawkings repeats it, I imagine he has not done any research/analysis himself, just repeating stuff he has read, an almost perfect example of Nobel Prize winner syndrome, perhaps.. Anyway Greenpeace liked it

    Did it and variations of, originate with James Hansen, or was it earlier?

    “In his book Storms of my Grandchildren, noted climate scientist James Hansen issued the following warning: “[I]f we burn all reserves of oil, gas, and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.”

    http://news.nationalgeographic.com/news/2013/13/130729-runaway-greenhouse-global-warming-venus-ocean-climate-science/

  5. Barry,
    I have no idea where it originated from. At least Hansen suggested it could happen if we burned everything (however, it would appear that even this is probably not correct). Hawking was claiming it could happen simply because Trump has withdrawn the US from the Paris climate agreement. That’s not only wrong, but highly exaggerated; withdrawing from the Paris agreement doesn’t mean that we’re suddenly likely to burn everything.

  6. Barry Woods says:

    quick Google shows Hawkings has been saying variations of this for years.
    2016:
    https://qz.com/695759/stephen-hawking-was-asked-to-explain-the-phenomenon-of-trump-couldnt/
    2014:
    https://www.washingtonpost.com/news/storyline/wp/2014/11/10/five-climate-lessons-from-stephen-hawking/?utm_term=.efafac319f30
    2007:
    http://www.independent.co.uk/environment/climate-change/prophet-of-doomsday-stephen-hawking-eco-warrior-433064.html

    And while other scientists have drawn back from spelling out the worst possible consequences of climate change – fearing being accused of sensationalism – he has been prepared to do so, repeatedly warning that global warming could run out of control so that “Earth might one day soon resemble the planet Venus”, with temperatures of 250C and sulphuric-acid rain.

    “very worried about global warming.” and Stephen Hawking’ said he was afraid that Earth “might end up like Venus, at 250 degrees centigrade and raining sulfuric acid.”
    Stephen Hawking’s Quote from 2006 International Conference on String Theory in Beijing

    well, I guess nobody was brave enough to tell him otherwise…. 😉 until now

  7. jsam says:

    Telling people is one thing. Having them absorb it is something else altogether.

    Right, Barry?

  8. Barry Woods says:

    If he thought that all these years I suppose that is why he signed an open letter to George Bush (along with George Soros and Harrison Ford) http://content.time.com/time/magazine/article/0,9171,104774,00.html

  9. jsam says:

    I spotted no error in the letter.

    Dear Mr. President:
    No challenge we face is more momentous than the threat of global climate change. The current provisions of the Kyoto Protocol are a matter of legitimate debate. But the situation is becoming urgent, and it is time for consensus and action. There are many strategies for curbing greenhouse-gas emissions without slowing economic growth. In fact, the spread of advanced, cleaner technology is more of an economic opportunity than a peril. We urge you to develop a plan to reduce U.S. production of greenhouse gases. The future of our children—and their children—depends on the resolve that you and other world leaders show.

    Respectfully,

    Jimmy Carter
    Mikhail Gorbachev
    John Glenn
    Walter Cronkite
    George Soros
    J. Craig Venter
    Jane Goodall
    Edward O. Wilson
    Harrison Ford
    Stephen Hawking

  10. Barry Woods says:

      In September 2000, world-renowned physicist Stephen Hawking was widely quoted in the press as being very worried about “runaway global warming.” (See story below) “I am afraid the atmosphere might get hotter and hotter until it will be like Venus with boiling sulfuric acid,” said Hawking. “I am worried about the greenhouse effect.”  
        http://www.eco-economy-hk.org/hawkingwarming.htm

    well, if he based “urgent”, based on him being incorrect about climate science, Earth becoming like Venus, that would be a bad judgement? Especially, if the other signatories only signed, because Nobel Prize winner scientist said we’d become like Venus to them and the wide press coverage of him saying that

  11. Barry,
    Okay, what are you expecting? That people go back in time and correct Stephen Hawking’s previous errors? I have no idea why he keeps repeating this despite it being wrong.

  12. Paul D Farrar says:

    Are the arguments of Houghton, _The Physics of Atmospheres_ on why the Earth can’t have a runaway greenhouse still considered valid? Also, wouldn’t we need some other chemical species to plug the holes in the water vapor spectrum?

  13. Paul,
    I’m not sure. As I understand Chris Colose’s argument in the Climate Feedback article is that the current Earth can’t really get to the point where it is absorbing more energy than it’s radiating to space. It could (theoretically) get to a moist greenhouse state, but not an actual runaway.

  14. Willard says:

    What are you expecting from BarryW, AT? He’s here to peddle the CAGW meme.

    Please don’t mention Lew.

  15. Barry Woods says:

    I just wonder how much influence he has had with it over the years? seems like he got Harrison Ford’s attention 😉 . Anyway, good that he has now been corrected, hope Richard Betts has a chat with him now.

  16. Barry,
    Given that I’ve been writing this blog for 4 years and this is the first time I’ve encountered him saying it, I would argue him making this claim has had little influence.

  17. JCH says:

    Recent one-dimensional (globally averaged) climate model calculations by Goldblatt et al. (2013) suggest thatincreased atmospheric CO2could conceivably trigger a runaway greenhouse on present Earth if CO2con-centrations were approximately 100 times higher than they are today.

  18. Barry Woods says:

    well, remember the Doomsday clock.. guess who.. is involved with that.. and his influence on the Royal Society? http://www.independent.co.uk/environment/climate-change/prophet-of-doomsday-stephen-hawking-eco-warrior-433064.html

  19. jsam says:

    If someone corrects Stephen Hawking will you correct Freeman Dyson, please.

    Thanks in advance.

  20. lerpo says:

    On Twitter, Robert Grumbine made the point that a Venus-like runaway is far less likely than something like an extinction-level asteroid strike, and we don’t exactly go around worrying about something like that (we do, however, commit some resources to keeping track of asteroids).

    Not just tracking, also redirecting!

    “The DART spacecraft will use an onboard autonomous targeting system to aim its crash at Dydimos B. It will collide with the small asteroid at a speed of 3.7 miles per second or 6 km per second, that is around 9 times faster than a shooting bullet. By observing its impact on Didymos B’s orbit around Didymos A, scientists will be able to study the effectiveness of the kinetic impactor technique as an asteroid mitigation strategy. The DART spacecraft is small in proportion to Didymos B, only cited to be the size of a refrigerator.” – http://interestingengineering.com/nasa-plans-deflect-asteroid-crashing-satellite-into/

  21. Paul D Farrar says:

    Colose seems to be similar to Houghton (who used older articles I haven’t seen, like Rasool and DeBergh). The surface T as function of water vapor pressure for Earth turns upward (positive feedback), but hits the saturation vapor pressure line. Venus starts at a higher T, and its curve misses the saturation line and keeps going until other, unspecified, processes (like running out of liquid water) take over.

  22. lerpo says:

    Given that I’ve been writing this blog for 4 years and this is the first time I’ve encountered him saying it, I would argue him making this claim has had little influence.

    Yeah. I only knew that he said it this time because of the refutations.

  23. Harry Twinotter says:

    Guy McPherson was peddling Venus-like runaway global warming a while back. I hope Hawking has not been reading his articles. I don’t recall he ever presented any evidence for his prediction.

  24. Lawrence Coleman says:

    His thinking correlates with other world experts in the field of climate science. James Lovelock who I have followed for many years also has said on many occasions that a venus like scenario is possible. We have never experienced such as rapid rise of CO2 in the leading role in such a short timeframe…ever. The dinosaurs even took 10,000 years or so to die out. Quite simply we are in uncharted waters. Waiting for the many gigatonnes of CH4 clathrates to be released under the arctic ocean and permafrost. Only a fool would say a venus scenario is an impossibility. Should the truth be known it is far more likely than you can imagine.

  25. Amazing, so in order to justify being considered “catastrophic warming” we must achieve runaway global warming?

  26. -1=e^iπ says:

    Good idea to call out Hawking on this. It’s important to prevent the public being mislead, so that policy decisions are made with the best available evidence and data.

  27. Lawrence,
    I think there are a couple of reasons why it’s unlikely for the current Earth. One is that a great deal of the CO2 on Earth is locked up in the lithosphere (which happened via weathering) so we cannot emit as much CO2 as is in Venus’s atmosphere. Also, for a true runaway you need to get to a state where there is more energy coming in than going out (causing the Earth to warm to the point where you’ve basically boiled away the oceans). Given current Solar insolation and how much CO2 and water vapour we could put into the atmosphere, this is regarded as not possible.

  28. Aaron Lewis says:

    It would not be our carbon emmissions that push Earth toward a Venus condition, it would be the carbon feedbacks. I do not think recent models capture carbon feedbacks. The best such models that I have seen were done long ago in Dynamo. I know they understated available free methane and clathrates. Carbon feedbacks are a “known unknown”.

  29. Aaron,
    Except, I think too much of the CO2 on Earth is locked up in the lithosphere (carbonate rocks) for even carbon feedbacks to push the current Earth towards a Venus-like runaway.

  30. Paul D Farrar says:

    Of course it doesn’t take that much warming to make significant areas uninhabitable. There are areas with large populations that are on the edge of human survivability, mainly in India and Pakistan. Even now, no meaningful outdoor work can be done in midday, seasonally. With a higher global temperature, a heat wave could kill large numbers, often within hours. The combination of large-scale death events and frequent restrictions on work (many of these areas depend on hard, outdoor labor) could force large populations to become heat refugees.

    Rather than worry about improbable heating, we need to prevent doable heating.

  31. -1=e^iπ says:

    “Of course it doesn’t take that much warming to make significant areas uninhabitable.”

    We already have large areas of the planet that are uninhabitable. It’s called the poles. If we cooled 1 degree, we would be making more of the planet uninhabitable.

  32. This is pretty silly because a warming of 6 to 8 degrees would be so catastrophic that this discussion would collapse along with the civilizations that support the discussion. We don’t have to encounter runaway warming that would produce a Venus-like atmosphere, we only have to warm the planet enough to trigger CO2 and NH4 releases to end life as we know it on the planet.

    uh-oh… cliff ahead…. is it a cliff that leads to a venus-like conclusion or only a cliff that will bash all our brains out? Yes, that’s an important question to wrestle with before we decide what to do about the cliff.

    Thank you, Mr. Hawking. It might be useful to have more people on the planet get more worried.

  33. -1,
    I think there is a difference between parts of the world today being essentially uninhabitable and us making regions that are heavily populated today into regions that are largely uninhabitable in ~100 years time.

  34. JCH says:

    The North Pole is an ocean, and yes, the ocean surfaces are largely uninhabited. People live on the coasts of the Arctic Ocean.

    Antarctica remains uninhabited by international agreement.

  35. -1=e^iπ says:

    “Thank you, Mr. Hawking. It might be useful to have more people on the planet get more worried.”

    This highlights a big problem. Some people think that it is moral to mislead the public and purposely misinform them in order to scare them into adopting mitigation. All for the greater good of course!

    I believe it’s called noble cause corruption.

  36. BBD says:

    Or just being mistaken.

    As opposed to deliberately twisting and misrepresenting absolutely everything like the, um, ‘contrarians’ do.

  37. JCH says:

    Un-noble cause corruption. Often accompanied with a rationalization that the behavior of some tiny fraction of scientists has so offended them they just had to pick up the sword for falsehood and evil.

    Officer, that boy scout’s behavior so offended me I had to start throwing little old ladies under buses to set the universe right.

  38. verytallguy says:

    This highlights a big problem. Some people think that it is moral to mislead the public and purposely misinform them in order to scare them into adopting mitigation. All for the greater good of course!

    I believe it’s called noble cause corruption.

    This highlights a big problem. Some people think that it is moral to mislead the public into believing honest misunderstandings, mistakes or disagreements are deliberate conspiracies,

    I believe it’s called bullshit.

  39. verytallguy says:

    Ack, even my poor quality satire verging on incoherent insult is rendered useless by html incompetence.

    I probably deserved it.

  40. verytallguy says:

    Wow, fixed so fast by mods that my own mea culpa makes no sense. Not sure if this is good or bad, but very impressive nonetheless.

  41. Just happened to check as you posted your comment. I’m not normally that efficient 🙂

  42. [Mod: Just redacting the first part of this comment] But I understand that -1 raised the question of morality with Hawking’s overstatement on runaway warming. It is really astounding to watch folks work to slow our global response to global warming and the sixth great extinction and then raise the question of morality. That takes testicles of great size, constructed of a copper zinc alloy. I think I hear them clanking. But that is all I will say on the matter. If people want to beat up on Stephen Hawking, why would I intervene? He’s a smart guy and can defend himself, right?

  43. The Very Reverend Jebediah Hypotenuse says:

    -1=e^iπ says:

    This highlights a big problem. Some people think that it is moral to mislead the public and purposely misinform them in order to scare them into adopting mitigation. All for the greater good of course!
    I believe it’s called noble cause corruption.

    Big problem? Not really.

    People should be damn scared. Alarmed, even.

    Personally, I can forgive Hawking for stepping over the line into “noble cause” advocacy – because he is on the right side of history.

    If you want something more sober, more measured, how about Hansen?


    2 degrees is actually a prescription for disaster. That’s actually well understood by the scientific community.

    We know that the prior interglacial period about 120,000 years ago – it’s called the Eemian in Europe –but it was less than 2 degrees C warmer than pre-industrial conditions and sea level was a least 6 to 8 metres higher, so it’s crazy to think that 2 degrees Celsius is safe limit.

    The only thing you can argue is that, well, it might take a while for the sea level to rise that much, but we know that it would happen because once the fossil fuels are burned to reach that level they are not taken out of the systems for millennia, and it does not require millennia for the ice sheets to disintegrate.

    That number (2 degrees) was chosen because it was convenient and thought that well that will give us a few decades so we can set targets for the middle of the century.

    Actually what the science tells us is we have an emergency, this is actually a global crisis and the science for that is crystal clear. It’s not obvious to the public because the climate system responds slowly, the ocean is 4 kilometres deep, these ice sheets are 3 kilometres thick. They only respond over timescales of decades to centuries, but once the processes are started it’s going to be extremely difficult if not impossible to stop them.

    The paleoclimate evidence indicates the ice sheets are much more sensitive than the glaciologist, the modellers of ice sheets have indicated and furthermore we now have satellite data over the last 12 years that confirms that ice sheet disintegration is a non-linear process that should not have been surprising, and I have been saying that for 10 years, but now this satellite data confirms that.

    The ice sheets are losing mass faster and faster with a doubling the of about 10 years. If that continues, we would get sea-level rises of several metres within 40 to 50 years.

    The consequences are almost unthinkable. It would mean that all coastal cities would become dysfunctional, some parts of the cities would still be sticking above the water but they would not be habitable, so the economic implications are incalculable. We really cannot go down that path, this is an issue of intergenerational injustice, it’s a moral issue…

    http://www.abc.net.au/radionational/programs/breakfast/two-degrees-of-global-warming-is-not-safe/6444698

    Hawking corrupt?

    Now that’s a crisis.

  44. Willard says:

    When some people start with “some people”, reach for your wallet.

  45. -1=e^iπ says:

    “That number (2 degrees) was chosen because it was convenient and thought that well that will give us a few decades so we can set targets for the middle of the century.”

    It was chosen by William Nordhaus in 1975 as an initial first guess. Interestingly, Nordhaus has moved well beyond his initial first guess as we can see by his DICE IAM. I think we should do the same.

    “The ice sheets are losing mass faster and faster with a doubling the of about 10 years. If that continues, we would get sea-level rises of several metres within 40 to 50 years.”

    Exponential sea level rise models are unphysical.

    I guess that could be another possible example of some people spreading misinformation (Hansen and his unphysical exponential sea level rise models).

  46. -1,

    Exponential sea level rise models are unphysical.

    Really? Care to provide a source?

  47. verytallguy says:

    I guess that could be another possible example of some people spreading misinformation

    The irony. It burns.

  48. -1=e^iπ says:

    @ ATTP – Climate models don’t show exponential sea level rise. See the IPCC AR5. Sea level rise by 2100 even under RCP 8.5 is less than 1 m (95% confidence level).

    But alternatively (if you want something simpler to understand), you can think about sea level rise as the convolution of temperature changes with a step sea level rise response function. If the response of sea level rise is very slow (which it is, hundreds of years) then this can be roughly approximated as sea level rise being a linear function of the integral of temperature. Since temperature is increasing roughly quadratically, this means sea level rise is cubic at best (not exponential). If you take a cubic fit to sea level rise over the past ~150 years or whatever you get a projection that agrees roughly with the predictions of climate models.

  49. -1,

    Climate models don’t show exponential sea level rise. See the IPCC AR5. Sea level rise by 2100 even under RCP 8.5 is less than 1 m (95% confidence level).

    Climate models do not include many of the processes that could lead to sea level rise. You could try reading this.

    But alternatively (if you want something simpler to understand)

    I think I may have pointed this out to you before, but I’m the only person allowed to be condescending here. Also, your explanation is reasonable but I don’t think it proves that exponential rise is unphysical (which is what you claimed).

  50. -1=e^iπ says:

    Sorry, my intent was not to be condescending

  51. BBD says:

    -1

    I guess that could be another possible example of some people spreading misinformation (Hansen and his unphysical exponential sea level rise models).

    You only get to say this if Hansen is proven wrong. Not only has this not happened, but the possibility that he is correct is very real. So who is spreading misinformation?

    How odd that you talk about future SLR as if it were driven by thermal expansion when we all know that later this century, ice sheet dynamics will become the main driver.

    That could be regarded as spreading misinformation too.

  52. The Very Reverend Jebediah Hypotenuse says:


    Exponential sea level rise models are unphysical.

    So are exponential atmospheric carbon dioxide level rise models.

    Your argument from incredulity also begs the question.

  53. -1=e^iπ says:

    @ BBD –
    “the possibility that he is correct is very real.”

    The possibility that the flying spaghetti monster exists is also very real.

    “as if it were driven by thermal expansion”

    When you raise global temperatures, sea levels will converge towards a new equilibrium for that temperature, this includes sea level rise due to ice melting. The idea that sea level rise is a roughly linear function of temperature convoluted with a step sea level response function is still valid.

  54. -1,

    The possibility that the flying spaghetti monster exists is also very real.

    Brilliant. Pseudo-anonymous person on internet criticises leading climate scientist. As far as I can tell, the worst case shown here is approximately exponential.

    When you raise global temperatures, sea levels will converge towards a new equilibrium for that temperature

    Well, yes. Please tell me you didn’t think that the suggestion was that it would be exponential for all eternity?

    To be clear, I don’t know if sea level rise could go through a phase where it is exponential. Your claim that this is unphysical, however, seems rather strong and is something you haven’t yet actualy backed up (other than waving hands wildly).

  55. The Very Reverend Jebediah Hypotenuse says:


    The idea that sea level rise is a roughly linear function of temperature convoluted with a step sea level response function is still valid.

    As a Pastarian who drinks tea from Russell’s teapot, I will merely allude to the fact that there is possibly an important difference between validity and soundness.

  56. Willard says:

    > You only get to say this if Hansen is proven wrong.

    Hansen could still be wrong and make a claim that is physically possible.

    Minus needs to show that Hansen’s claim is impossible on physical grounds.

  57. BBD says:

    Ah, well then, he’s in trouble. Because that step function bit he mentioned would presumably be exponential SLR. It’s a timescale thing, it seems.

  58. Willard says:

    > there is possibly an important difference between validity and soundness.

    Economists seldom expect logical inquisitions.

    From the redundant department of redundancy:

    There is a considerable difference in future projections for sea-level rise between process-based models and the semi-empirical model. A problem associated with the projections based on the semi-empirical model is assuming that sea-level change in the future will have the same relationship with the past, as the relationship is calibrated with the past record of the GMSL rise. However, it is not certain whether the past relationship will hold in the warmer world, because the climate system undergoes complex interactive changes, and rises in air temperature and GMSL may show a non-linear relationship. More effort is needed to resolve the reason for the large difference in the future projections between the two models. Nevertheless, a possibility cannot be excluded that the GMSL rise will exceed 1 m by the end of this century if climate change proceeds along a high temperature increase pathway.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758961/

    Cue to Olivia Newton-John.

  59. The Very Reverend Jebediah Hypotenuse says:


    Minus needs to show that Hansen’s claim is impossible on physical grounds.

    WIth that proof out of the way, -1 can then move back to Hawking’s hawking.

    Or, if you want something simpler to understand:
    http://www.projectmidas.org/blog/calving/

  60. -1=e^iπ says:

    Maybe we can infer something about climate sensitivity from Venus going runaway as Venus was supposedly a very Earth-like planet when it started out.
    Consider a simple linear feedback model ECS = A/(1-f), where A = 1.15C is the no feedback climate sensitivity and f is the feedback strength. Since Venus is ~70% of the distance to the sun, it receives ~2x the solar radiation. This means that for the most part the feedbacks are twice as strong (ex. twice as much incoming radition -> twice as much outgoing radiation -> twice as much increase in radiative forcing due to a similar change in water vapour).
    Now there are some things that are not included in ECS, but these other factors tend to become negligible as the planet gets warmer. The ice-albedo feedback goes to zero as you run out of ice. And the CO2-temperature, CH4-temperature and N2O-temperature feedbacks go to zero as temperature increases since radiative forcing from CO2, CH4 and N2O are logarithmic / square-root functions of concentration while the concentration increase as a function of temperature is linear at best.
    As Venus went runaway, this means that 1-2f should be less than or equal to zero. 1 – 2f = 0 => f = 0.5 => ECS = A/(1-0.5) = 2.3 C.
    So Venus going run away suggests to us that feedbacks should at least double the non-feedback climate sensitivity and ECS should be 2.3 C or greater.
    Does this make sense?

  61. -1=e^iπ says:

    Found this old blog post by Judith Curry, where she states:
    “Myhre and Stordahl found a 12.7% difference between CO2 radiative forcing with clouds versus clear sky”
    https://judithcurry.com/2010/12/11/co2-no-feedback-sensitivity/

    Never really thought about cloud impact on no-feedback sensitivity (always assumed you could get it for the most part with basic back of the envelope calculations).

    So I guess the above should say that Venus being runaway suggests to use that ECS is 2.0 C or greater.

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