IPCC AR6 WG1

The site has been a little quiet, but since this blog has been going long enough to have commented on the release of the IPCC AR5 WG1 report, it only seems right to comment on the release of the IPCC’s AR6 WG1 report. In case anyone doesn’t know, the IPCC is the Intergovernmental Panel on Climate Change, AR6 is the sixth Assessment Report, and WG1 is Working Group 1, the Physical Science Basis.

I haven’t read much of the main report, but have read through the Summary for Policy Makers (SPM). The bottom line is that the big picture hasn’t really changed; it’s real, it’s us, there’s strong agreement amongst relevant experts, the impacts could be really severe, we can still do things to limit the impact.

However, I thought I would highlight some of the things that caught my eye, and maybe others can provide other explains in the comments. One of the key highlights in AR5 was that it was extremely likely that most of the observed warming was anthropogenic, and that hasn’t changed: The likely range of total human-caused global surface temperature increase from 1850–1900 to 2010–2019 is 0.8°C to 1.3°C, with a best estimate of 1.07°C (i.e., it’s probably all human-caused).

What does seem to have changed is there seem to be stronger statements about extreme events, in particular heatwaves and extreme precipitation, but also droughts, flooding and tropical cyclones. For example, there is a pretty clear statement that climate change [is] already affecting every inhabited region across the globe with human influence contributing to many observed changes in weather and climate extremes.

The AR6 report also presented a narrower likely range for equilibrium climate sensitivity (2.5oC to 4.5oC) and – unlike AR5 – presents a best estimate of 3oC. It also presents a slightly narrower range for the Transient Climate Response to Cumulative Emissions (TCRE) of 0.27oC to 0.63oC per 1000 GtCO2, with a best estimate of 0.45oC (or 1.65oC per 1000 GtC).

There also seem to be stronger statements about many of the changes, and the current state, being unprecedented over many centuries to, potentially, thousands of years. The report now specifically states that it is more likely than not that no multi-centennial period after the Last Interglacial (roughly 125,000 years ago) was warmer globally than the most recent decade.

There’s plenty more that I could highlight, but overall it seems to be mostly strengthening the basic understanding that we’ve had for quite some time now. Maybe we’ll see less of the “climate change isn’t influence extreme events” narrative that some like to promote, but I wouldn’t bank on it.

If you want to read some other takeaways from AR6 WG1, Realclimate has a new post. As I said above, maybe others could highlight their takeaways in the comments and, if interested, make any others points they might like to make.

Links:

IPCC AR6 WG1 report – Link to the AR6 WG1 report.
IPCC AR5 WG1 post – my post about the release of the AR5 WG1 report in 2013.
AR6 of the best – Realclimate post about the release of the AR6 WG1 report.

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85 Responses to IPCC AR6 WG1

  1. Ben’s comment reminded me that I also thought it did quite a good job of stressing the need for CO2 emission reductions, while also pointing out that it’s important to also reduce the emission of other GHG species.

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  3. I have not read the (summary of the) report yet, but I noticed on social media that the IPCC now calls it *indisputable* that global warming is due to human activity.

    In previous reports they always claimed that there was still a few percent chance it was not and, attribution is not my field, but I have always wondered where that percentage came from. Looking at all the different lines of strong evidence for such a basic claim it looked like cowardice to me. Did they worry that a moon-sized monster of Loch Ness would appear from the bottom of the Pacific and claim its army of fairies to be responsible?

  4. Yes, it now says [i]t is unequivocal that human influence has warmed the atmosphere, ocean and land.

  5. A few thoughts. AR6 has made additional steps compared to AR5, with about 1/3rd of the report on regional aspects. It seems also to have made efforts to improve the readability and presentation e.g. SPM.3 and other ‘innovations’ such as the climate ‘impact drivers’ in SPM.9. The FAQ1.1 table in the full report includes a useful summary of how the science has evolved from 1990 to now (some open questions now ‘closed’). The interactive map is another innovation in sharing the science. So for non-scientists, it feels like it will be more accessible, easier for policy makers to use to drive action (because of more regional data, and assuming they are serious!). Has anything fundamentally changed? No and Yes. No, the underlying message is the same, but Yes, it is looking sharpers and many details are becoming sharper (e.g. the link to extreme weather events).

  6. Richard,
    Yes, I think they have made the message clearer and the information more accessible. As Victor points out, they’re pretty definitive about the human activity being the cause, and they’ve used terms like “unprecedented” and “unequivocal”, which makes things pretty clear.

  7. Ben McMillan says:

    Zeke Hausfather’s take on it, covering some of the same ground, but with extra graphs:

    And a comprehensive in-depth from carbonbrief, almost as long as the SPM itself.

    https://www.carbonbrief.org/in-depth-qa-the-ipccs-sixth-assessment-report-on-climate-science

  8. jacksmith4tx says:

    Zeke did a magnificent job of organizing the flood of data from the report, Bravo!
    There is always one scenario they omit when they do their climate analysis: global nuclear war. But that aside, it’s depressing enough considering the the other raging pandemic, “Behavioral Sink Syndrome”, is destroying our social cohesion which will stifle any collective response.

  9. Willard says:

    Rachel has a post with a TL;DR I really like:

    Another report and the message on climate change is still the same – our emissions must be zero

    https://rachel.blog/2021/08/09/another-report-and-the-message-on-climate-change-is-still-the-same-our-emissions-must-be-zero/

  10. angech says:

    What else is a panel on Climate Change, unspecified expected to find?
    The Climate is not changing and we do not have a reason for existing?
    They have no choice and no insight.

    It’s like what other reason for existing does a climate alarmist have for existing [Willard, Zeke]] other than to promote climate alarmism.?

    The two pertinent questions the IPCC does not consider and has never answered are
    What is the optimal temperature for life on earth?
    What is the optimal level for CO2 levels on earth?
    .

    These basic questions and their answers should be front and centre of the IPCC manifesto.

    Perhaps ATTP could expand on this point with another post dedicated to these two questions.
    Please.

    After all, is the optimum temperature some time in 1850 when we first determined the capacity to determine and record temperatures around the globe. Why is it the best temperature rather than 2 or 3 degrees warmer which led to the most prolific times for expansion of life on earth.?

    What makes the 1900 level of CO2 and the preceding millennia so special?
    Does having a low level of CO2 brought about by the burial of immeasurable amounts of CO2and the lack of building up of levels due to repeated ice ages stunting growth really determine what an adequate amount of CO2 for both animal and vegetative lives need?

    Should we really be back at higher levels to encourage growth and food production and evolution?
    What is the right level of CO2.
    – Optimum Temperature.
    – Optimum CO2
    Why does the IPCC insist that change is dangerous without specifying exactly where we should be and why we should be there?
    Have posted this at JC with similar request.

  11. angech,
    This isn’t really about there being an optimal temperature, or optimal CO2 level. It’s about us changing the climate to which we (and most other ecosystems) have adapted on a timescale that is geologically fast. If, by chance, atmospheric CO2 had been 600ppm for the last ~10000 years and temperatures been 2C warmer than it is today, we’d have developed our civilisations in that climate. The problem is the likely disrupting that a rapidly changing climate will bring and whether or not we should be actively trying to limit this through reducing how much we end up emitting.

  12. Willard says:

    While the Rational Wiki has a nice description of Just Asking Questions, here’s an explanation as to why contrarians always ask the same questions:

    Asking questions is only a good idea if you are willing to accept the answers to those questions. In other words, asking a question like, “is coronavirus man-made” is fine if it is being asked out of a genuine sense of curiosity and desire for knowledge. There is nothing wrong with asking that question if you are then willing to look at the evidence and accept the answer provided by that evidence (in this case, the answer is a clear, “no, it was not man-made”). The problem is that many people asking the question won’t accept that answer. They refuse to accept the evidence, but also don’t want to admit that they are denying evidence. So, instead, they claim to be “just asking questions.”

    https://thelogicofscience.com/2020/05/31/the-problem-with-just-asking-questions/

  13. Thomas Fuller says:

    I think Angech’s questions do need to be answered, although their timing and placement within the context of AR6’s release is unfortunate.

    Charting change is an important element of understanding its consequences. Today’s climate might be more ‘productive’ for greenery than 1850s. The question is will it be as benign in 2100, 2200 or 2300. And that question does need to be answered, and really hasn’t been yet.

    But charting the change is important.

  14. Willard says:

    > that question does need to be answered, and really hasn’t been yet.

    Both claims are false.

  15. Joshua says:

    Angech –

    > It’s like what other reason for existing does a climate alarmist have for existing [Willard, Zeke]] other than to promote climate alarmism?

    What reason other than calling people “alarmist, ” as a way of demonizing those you disagee with, do you have for existing?

  16. Tom,
    Yes, I don’t think the questions*needs* to be answered and it mostly has been, even if people don’t like the answer.

  17. Willard says:

    A more important reason is to beg the question at hand, J:

    The critical square of the whole ClimateBall Bingo. This square begs the most important question of all Climateball, i.e. that AGW won’t have any alarming consequences. We just don’t know. #ButCAGW is more or less synonym.

    “But Alarmism”

  18. Thomas Fuller says:

    The 12 chapters of AR6 do not include one on impacts. Hence I must refer back (yet again) to the AR5 Supplementary Report on Impacts and Adaptation, found here: https://www.ipcc.ch/report/ar5/wg2/. If impacts are addressed in AR6, please let me know where.

    There will undoubtedly be negative impacts due to climate change. I for one do not contest human actions as one of the primary causes of these changes. However, I submit that Angech’s questions are not answered as of this moment.

  19. Tom,
    This has just been the release of the WG1 report (the Physical Science Basis). The WG2 and WG3 reports are released next year (IIRC).

  20. Willard says:

    > do not include one on impacts.

    First sentence of the SPM:

    This Summary for Policymakers (SPM) presents key findings of the Working Group I (WGI) contribution to the IPCC’s Sixth Assessment Report (AR6)1 on the physical science basis of climate change.

    Source: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf

    Asking questions is good. Asking coherent questions is better.

    I submit that our luckwarm fellow hasn’t checked at the proper place.

  21. Thomas Fuller says:

    willard, some of us are constrained by other duties, like working for a living. I hope to begin reading AR6 this weekend. Thanks for your warm consideration of the difficulties some of us contend with.

  22. Thomas Fuller says:

    Here are the two questions Angech asked:
    “What is the optimal temperature for life on earth?
    What is the optimal level for CO2 levels on earth?”

    Given that the IPCC has never been tasked with answering these questions, it’s a bit unfair to criticize them for not having provided the answer.

    But I will repeat, these are important and reasonable questions.

  23. Willard says:

    > these are important and reasonable questions.

    These are neither. They are usually ways for contrarians to conceal the idea that we need to state an optimal temperature or optimal level before we [insert your favorite meme related to “but politics”].

    As for never being answered, well, that’s just preposterous. Here’s one:

    Dr. James Hansen, the top climate scientist in the US has just announced his retirement from NASA.

    He’s been one of the best advocates a planet could ask for — he even gave us our name when he wrote that 350 parts per million is the safe level of CO2 in the atmosphere.

    https://350.org/46-years-science-and-courage/

    That was 46+8 years ago.

    I thought Jim’s ideas were welcome by our luckwarm clique.

  24. Thomas Fuller says:

    I believe you are incorrect, willard. ‘Contrarians,’ like every other faction, will of course use whatever they can to further their goals. Nonetheless, the questions remain both important and reasonable.

    And since when does ‘safe’ equal ‘optimal?’ Perhaps the goal should be even lower. I personally doubt it, but it’s certainly possible.

  25. Tom,
    Again, I disagree that these are important questions. The issue is climate *change* and what sort of impact this changing climate will have on our current civilsations, and on ecosystems. It’s quite possible that at some point in the future we will be in a climate where we can thrive and new ecosystems will emerge. The issue, though, is how disruptive will it be to get there.

  26. Thomas Fuller says:

    Hi ATTP,

    Great–now I’m disagreeing with you and willard both. Sigh…

    I think Angech’s questions are reasonable and important because it’s good to have a positive goal, rather than just a ‘do not exceed’ limit. I’m not suggesting there’s a Nirvana or Utopian level of temperature, CO2, etc., but, if I can borrow the term, an optimum range for the principal actors involved.

  27. Willard says:

    > it’s good to have a positive goal

    Since when “positive” implies we know what’s optimal?

    Here’s a positive goal:

    An IPCC special report on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty.

    https://www.ipcc.ch/sr15/

    One way to test if a question is important for some contrarian C is to ask C if and where they checked.

  28. David B Benson says:

    The optimal concentration of carbon dioxide in the atmosphere is that which prevailed before industrialization, i.e., 1750; 275 ppm.
    See David Archer’s “The Long Thaw” and research papers by Ganapolski, often with Archer.

  29. Bob Loblaw says:

    I think Angech’s questions are reasonable and important

    They are bull$#^ questions. “Optimal” for what? Bacterial growth? For bacteria that live in humans, 37C. That’s why fevers are a good defense mechanism. Optimal for permafrost stability? Definitely not 37C.

    Optimal for human habitation? For tree growth? Tropical or boreal? For crop growth? Rice, or wheat, or corn? For road safety?

    Angech’s questions deserve no better answer than “42”. If he (or you) honestly believes that the myriad of natural and human systems can be summed up in one “optimal” number for temperature or CO2, then he (or you) are even more of a fool than he (or you) normally appears to be.

    It’s a “what’s the meaning of Life, the Universe, and Everything?” type of question.

  30. mrkenfabian says:

    In the guise of just asking questions the idea that the world might be better because of global warming is introduced into the discussion in a deniable manner. It is a popular argument amongst opponents of climate and emissions accountability, I suspect because, by questioning what is “optimum” it evades consideration of the problems arising from change itself, which we know with high confidence will be damaging to most existing agriculture, infrastructure, people and remnant natural ecosystems.

    I would expect that for much of remnant natural ecosystems the pre-industrial conditions might be considered optimal – species’ ability to adapt by migration is limited and some won’t survive well enough to adapt by evolution. It is a nice notion that we might return the world to such a state but I see neither the means to achieve that or the will to commit to it; effective responses to global warming look constrained to aiming for a new, warmer climate equilibrium, not a return to pre-industrial. Not really a matter of picking and choosing what new equilibrium is best but achieving a new, hopefully steady climate state.

  31. Brandon Gates says:

    Angech, Tomas, et al.,

    At risk of piling on, in the distant past mass extinctions occur over the same temperature ranges when populations were exploding. Hence, no “optimal” temperature. Supposing otherwise entails but stoopid modulz, another favorite contrarian escape hatch.

    What empirical evidence suggests is that rapid departures from local norms is what causes mass die-offs. It’s not the absolute temperature which matters most but rather how fast we get there. If avoiding rates of change consistent with >90% extinction events isn’t a positive goal, I don’t know what is … and I take it that not knowing is the point.

    c.f. but warmer is better.

  32. Thomas Fuller says:

    Brandon, that makes a lot of sense.

  33. Brandon Gates says:

    Thomas, thanks.

  34. Thomas Fuller says:

    We see evidence of that in modern humans. Cold deaths and warm deaths occur in hot and cold climes, but at very different temperatures. Finns suffer from heat at temperatures that have Floridians reaching for a sweater and the obverse is also true. It’s the change from a long-established norm that has an effect.

  35. Brandon Gates says:

    Thomas, I agree with most of what you say but I’d point out that what all humans consider comfortable lies within a range that is much tighter than the swing in temperatures from equator to poles. It’s the rest of the biosphere that would be impractical to air condition which will bear the most direct brunt of rapid departure from local long-term means.

  36. The other obvious issue with the “just use airconditioners” narrative, is that even if it is possible to adapt to climate change through using technological solutions, doesn’t mean that it’s ethically acceptable for one group to continue doing something that will then require another group to invest in infrastructure that will allow them to cope with the changes that may have done little to produce.

  37. Steven Mosher says:

    What is the optimal temperature for life on earth?
    What is the optimal level for CO2 levels on earth?

    there is no optimal temperature for life on earth. no single temp that will optimize some aspect of life
    nevertheless we know -5C would be a bad thing. and 50C would be a bad thing. we know ranges
    and risks with extremes

    i asked my doctors for my optimal weight
    they gave me a range not less than X not more than Y
    they said 200lbs was not good but didnt give an optimal. they gave an average
    and danger levels

    they said i was at increased risk, but because they couldnt say 187.78 lbs exactly
    i pretty much ignored them. asking for optimal is not a good idea. if youre going to ignore
    the answers science Can give you.

    for most life on earth earth we might say not less than 0C not more than 35C
    14C has been pretty good for us. if it aint broke!!

  38. Steven Mosher says:

    Angech
    is their an optimal time for you to leave for work in the morning

    or is there a window or range of times. some too early others too late

  39. JCH says:

    It’s the temperature range where my favorite trees, if need be, have time to move to safety.

  40. Willard says:

    The “normal” body temperature is a construct. Here’s a slightly edited transcript of a cool episode:

    MOLLY WEBSTER: But anyway, Deanna told me there’s a couple of things to know about the 1800s for the purposes of our story. One is that fevers back then weren’t seen as some sort of, like, signal or sign of a disease.

    DEANNA DAY: The fever was just the disease.

    MOLLY WEBSTER: They thought fevers were the actual illness.

    DEANNA DAY: The thing you had that was causing all of your symptoms.

    […]

    MOLLY WEBSTER: Yeah. But then along came a guy named Carl Wunderlich.

    LULU MILLER: Cool name.

    DEANNA DAY: So Wunderlich was a physician in Germany and…

    MOLLY WEBSTER: He was the chair of medicine at the University of Leipzig. And he was one of the first people, one of the first doctors to use thermometers in his clinic. At the time, they were like 2 feet long and took 20 minutes to take a temperature. And in the 1850s, when Wunderlich was doing his thing, it was, like, an era when big data was becoming king, which is funny because he wouldn’t actually think about that because there were no computers.

    LULU MILLER: There were lots of pencils.

    MOLLY WEBSTER: Yeah, lots of pencils, lots of paper. And so his thing that he was like – OK, the data that I’m going to collect is I want to understand how temperature of a human body changes throughout the progression of an illness. And so…

    DEANNA DAY: At his hospital, they took temperature readings repeatedly over and over from about 25,000 patients.

    MOLLY WEBSTER: Twenty-five thousand patients, a million and a half temperature recordings.

    LULU MILLER: Did he have a fleet of temperature collectors?

    MOLLY WEBSTER: No, it was basically him and whoever worked in his clinic. He just had a really busy clinic in Germany.

    LULU MILLER: Wow. That’s like – that feels but I guess over, like, decades, right?

    MOLLY WEBSTER: Yeah, like, 20 years. So Wunderlich collects all this data. And…

    DEANNA DAY: The 19th century version of crunching the numbers and created all of these charts.

    MOLLY WEBSTER: Fever charts.

    DEANNA DAY: He found different diseases had different fever progressions in patients.

    […]

    DEANNA DAY: And kind of incidentally, he was like, and in healthy people, when they are no longer sick, we have found that body temperature is 37 degrees Celsius.

    MOLLY WEBSTER: Which is – the conversion to Fahrenheit is 98.6.

    LULU MILLER: Interesting. So he was just like, oops, I was studying this other thing. I accidentally have a kaj-million (ph) data points.

    MOLLY WEBSTER: Yeah. It was essentially a footnote.

    LULU MILLER: Ninety-eight-point-six – that thing we all sort of bow before – was just a little footnote from the 1800s?

    MOLLY WEBSTER: Well, yes, until this guy came along named Edouard Seguin.

    DEANNA DAY: Edouard Seguin is the person who actually translated Wunderlich’s work and introduced it to the United States.

    MOLLY WEBSTER: And he’s really into thermometry.

    LULU MILLER: Which is a word.

    MOLLY WEBSTER: Which is a word. I know.

    DEANNA DAY: He writes this manual called “Family Thermometry,” which is supposed to teach moms how to take their kids’ temperature and why it’s important and how to do it.

    MOLLY WEBSTER: And so Seguin, along with thermometer companies, kind of went on this big push through, like…

    DEANNA DAY: Articles in Good Housekeeping and Ladies’ Home Journal and Scientific American.

    MOLLY WEBSTER: To talk about thermometers and make them, like, a new tool for the home.

    DEANNA DAY: And there are advertisements in all kinds of publications.

    MOLLY WEBSTER: And over and over again, they’d hammer on this number – 98.6, 98.6. That’s what you should be. That’s what your kids should be. And I feel like this, like, marketing campaign that happened at the end of the 1800s and the early 1900s is essentially been handed down to us through the century and made us think that 98.6 is the normal or ideal temperature for a human body, which is bullsh**.

    (LAUGHTER)

    CATHERINE LEI: Well, it turns out that there’s a lot of variation across all these different parameters.

    MOLLY WEBSTER: So this is Catherine Lei.

    CATHERINE LEI: Infectious disease epidemiologist at Stanford University.

    MOLLY WEBSTER: And as Cat explained it to me, there is no one healthy human temperature.

    CATHERINE LEI: Women have higher temperatures than men.

    (SOUNDBITE OF MUSIC)

    CATHERINE LEI: Bigger people have higher temperatures.

    MOLLY WEBSTER: Fatter and skinnier people have different temperatures.

    CATHERINE LEI: Taller people have lower temperatures.

    LULU MILLER: Woah.

    MOLLY WEBSTER: They’re just so thinned out that they got surface area for days?

    CATHERINE LEI: (Laughter) I don’t know.

    MOLLY WEBSTER: Hormones can change your temperatures. Morning and night can change your temperatures.

    CATHERINE LEI: Younger people have higher temperatures than older people.

    LULU MILLER: I’m already thinking about the sweatsuits I want to rock. OK.

    MOLLY WEBSTER: And even in the same person, temperature taken in the ear, in your armpit and your butt can vary by, like, two degrees.

    LULU MILLER: Wow.

    MOLLY WEBSTER: Now, all this variation piles up to an average of 98.6. But just to really crack this thermometer wide open – and you might remember this from the episode I did last summer, Fungus Amungus – researchers don’t even think 98.6 is our average anymore.

    LULU MILLER: What?

    MOLLY WEBSTER: Like, there was just a new paper a year ago that said it looks like the sort of average of a healthy kind of Western population is 97.5. And Cat was actually involved in that research, and she said that it looks like our temperature has been dropping .05 degrees Fahrenheit every decade since the 1850s.

    https://www.wnycstudios.org/podcasts/radiolab/articles/kleptotherms

    The history of science is great. Climateball players should study it more.

  41. Thomas Fuller says:

    You’re the only Climateball player in 2021, willard. You created it. You then killed it. Pity, that.

  42. Brandon Gates says:

    Yup, looks like Climateball to me, W. Same plays different days. I couldn’t help but play a round for old times’ sake:

    > Not just some heat waves, but every heat wave. And not just those that are going to happen in the future, but all those that are happening today. Apparently, heating has that effect. It just can’t help but make things hotter, no matter what their current temperature and no matter when it is applied.

    A rising tide raises all boats, John R. It works better for physical tides than economic ones but that’s a different discussion. What doesn’t rise with tides are sea walls. A rogue wave is less likely to slosh over the dike at low tide than high tide. One almost has to not want to get it to not get it.

  43. Thomas Fuller says:

    willard wrote, “AT is still waiting for you to show where the IPCC says that climate change doesn’t threaten our civilisation.”

    https://www.ipcc.ch/report/ar5/wg2/.

  44. Steven Mosher says:

    Yup, looks like Climateball to me, W. Same plays different days. I couldn’t help but play a round for old times’ sake:

    nobody escapes the matrix

    folks at clisep be black pilled.
    when they need to be orange pilled
    ya’ll need that orange pill and laser eyes

  45. Willard says:

    First hit for “civiliza”:

    11.8.2. Limits to Food Production and Human Nutrition

    Agricultural crops and livestock similarly have physiological limitations in terms of thermal and water stress. For example, production of the staple crops maize, rice, wheat, and soybean is generally assumed to face an absolute temperature limit in the range of 40°C to 45°C (Teixeira et al., 2011), while key phenological stages such as sowing to emergence, grain-filling, and seed set have maximum temperature thresholds near or below 35°C (Yoshida et al., 1981; Porter and Gawith, 1999; Porter and Semenov, 2005 ). The existence of critical climatic thresholds and evidence of nonlinear responses of staple crop yields to temperature and rainfall (Brázdil et al., 2009; Schlenker and Roberts, 2009; Lobell et al., 2011b) thus suggest that there may be a threshold of global warming beyond which current agricultural practices can no longer support large human civilizations, and the impacts on malnourishment and undernutrition described in Section 11.6.1 will become much more severe. However, current models to estimate the human health consequences of climate- impaired food yields at higher global temperatures generally incorporate neither critical thresholds nor nonlinear response functions (Lloyd et al., 2011; Lake et al., 2012), reflecting uncertainties about exposure-response relations, future extreme events, the scale and feasibility of adaptation, and climatic thresholds for other influences such as infestations and plant diseases. Extrapolation from current models nevertheless suggests that the global risk to food security becomes very severe under an increase of 4°C to 6°C or higher in global mean temperature (medium evidence, high agreement) (Chapter 7, Executive Summary).

  46. Steven Mosher says:

    What empirical evidence suggests is that rapid departures from local norms is what causes mass die-offs. It’s not the absolute temperature which matters most but rather how fast we get there.

    same thing we found in heat waves.
    rapidly going from 80F to 103 for a few days in the spring when residents are not adapted to it
    –think chicago– is worse than being at 105F for days in july — thibk phoeix

    its the the rapid change from what you are accustomed to or adapted to is what kills you.

  47. Steven Mosher says:

    https://journals.physiology.org/doi/full/10.1152/physiol.00040.2018

    Although heat waves may occur for only a short duration relative to an animal’s entire life, heat waves need only occur once during the pre-reproductive developmental period to strongly reduce reproductive success (14, 127). Since reproductive success is a complex interaction of organismal traits and ecological interactions, ecosystems will change as the environment changes, since each member of an ecosystem has its own response to environmental change. To understand the impacts of environmental change on physiological adaptation, we must consider selection for organismal traits in the context of the changes in an organism’s habitat (59) as well as changes in the ecosystem they are a part of, especially species interactions such as mutualisms (123), competition (49), predator-prey (111), and host-parasite (85), and the prevalence and penetration of infectious diseases, such as the temperature-sensitive response to the densovirus causing sea star wasting disease outbreaks during marine heatwaves (8, 68, 82).

  48. Dave_Geologist says:

    It’s in the nature of “normal science” that after a while the consensus stays the same but the uncertainty range narrows.

  49. Willard says:

    Next occurence:

    Relationships are explored using statistical analysis and data derived from archaeological and other historical records. For example, the timing of the collapse of the Khmer empire in the Mekong basin in the early 15th century corresponds to an unusually severe prolonged drought (Buckley et al., 2010). DeMenocal (2001) summarizes evidence that suggests that major changes in weather patterns coincided with the collapse of several previously powerful civilizations, including the Anasazi, the Akkadian, Classic Maya, Mochica, and Tiwanaku empires. Other historical reference points of the interaction of climate with society emerge from analysis of the Little Ice Age. Some studies show that the Little Ice Age in the mid-17th century was associated with more cases of political upheaval and warfare than in any other period (Parker, 2008; Zhang et al., 2011), including in Europe (Tol and Wagner, 2010), China (Brook, 2010), and the Ottoman empire (White, S., 2011). These studies all show that climate change can exacerbate major political changes given certain social conditions, including a predominance of subsistence producers,conflict over territory, and autocratic systems of government with limited power in peripheral regions.The precise causal pathways that link these changes in climate to changes in civilizations are not well understood due to data limitations. Therefore, it should be noted that these findings from historical antecedents are not directly transferable to the contemporary globalized world. The literature urges caution in concluding that mean future changes in climate will lead to large-scale political collapse (Butzer, 2012).

    That’s in 12.5.1. Climate Change as a Cause of Conflict.

  50. paulski0 says:

    Seems to have gone slightly under the radar but there is quite a big change in assessed aerosol forcing strength, which was presumably a large factor in the ECS assessment update. -1.3W/m2 in AR6 for 1750-2014 compared with -0.9W/m2 in AR5 for 1750-2011. Within that the aerosol-cloud component estimate in AR6 is almost double that in AR5.

  51. Paul,

    Thanks. I did notice that it seemed a bit higher, but hadn’t checked. I also think the ERF for a doubling of CO2 might be slightly bigger too (3.9 W/m^2, rather than 3.7 W/m^2).

  52. Chubbs says:

    Observed warming has also been increased a bit in AR6. Per Chris Smith’s twitter, the AR6 value is 1.30C warming for 2019 vs 1750. With forcing over the same period of roughly 0.7 of 2X CO2, my noodling gives a TCR of 1.9, Hard to fuel an ECS debate with those #.

  53. Brandon Gates says:

    Mosh, thank for that paper it is an interesting read. Two things jumped out at me:

    When high temperatures become extreme enough to cause direct damage to proteins by breaking the weak bonds that maintain protein tertiary and quaternary structure, the cellular stress response is induced (69). In this response, additional ATP is diverted to the expression and function of molecular chaperones (e.g., HSPs) that attempt to repair the damage to unfolded or misfolded proteins (19).

    […]

    In species with multiple copies of a gene, the loci may evolve differences in primary structure that lead to different thermal properties (i.e., thermally adapted paralogous homologs), and differential expression of those genes can be involved with thermal acclimation, as in the above-mentioned thermoTRPs, and has also been demonstrated in myofibrilar proteins (113). Where multiple loci for a gene are not available, there is potential for allelic variants to be differentially expressed—a phenomenon that has often been characterized as important for thermal adaptation of populations (25, 100) but is not well supported by evidence for plasticity within individuals (113). Some organisms possess enhanced capacity to produce proteins with diverse thermal properties from a single gene by editing the mRNA transcripts from that gene before translation.

    Repairing damaged proteins and on-the-fly, on-demand mRNA editing … mind blown.

    The WGII lot are really up against it.

  54. Steven Mosher says:

    Mosh, thank for that paper it is an interesting read. Two things jumped out at me:

    yes. sometinmes stupid questions” optimal T?” leads other people to find cool stuff

  55. Jeffh says:

    I have not visited this site recently, and then I come in here and see non-ecologists debating and discussing what their limited understanding of the field perceives to be ‘optimal temperature’ for biodiversity. As always, as someone who does possess the relevant expertise, I find some of the comments disturbing, lacking an appreciation of the importance of scale.

    The critical point – repeated ad nauseum by ecologists and environmental scientists – is not what the supposed ‘optimal’ temperature is but how much variance there is around climate control mechanisms at large scales where change is slow and thus much more deterministic. In other words, when there is change, the question is the rate of change or how long it takes to go from one abiotic condition or state to another. In this context, the biosphere is warming more rapidly than in hundreds of thousands of years and perhaps many millions of years. Locally, of course, these changes are occurring even more dramatically. Placed this against a tapestry of a suite of other anthropogenic stresses across the biosphere and the prognosis for much of biodiversity is quite literally dire.

    When the ‘Great Dying’ occurred at the Permian-Triassic boundary some estimates are that the surface temperature of the Earth increased by around 8 degrees over 100-200 centuries, perhaps as a result of intensive short-term volcanism (this is longer than human civilization). This temperature rise and attendant acidification of the oceans was enough to drive the greatest mass extinction in our planet’s history: some 75% of terrestrial and 95% of marine species disappeared. Bear in mind that the current rate of warming exceeds the P-T warming event by 10 to 30 times. Again, place this in the context of habitat loss and fragmentation, chemical pollution, over-harvesting, invasive species and other human-mediated processes on natural systems and we are facing a calamity of epic proportions in which climate warming amplifies the effects of these other stressors.

    The planet already has lost immense amounts of genetic diversity as a result of the human assault, and genetic diversity represents one of the important tools for rapid adaptation to biotic and abiotiic factors (via selective sweeps). We can see biodiversity across a broad taxonomic range of vertebrate and invertebrate taxa declining rapidly; nowhere is this more apparent than in insects, but of course all of biodiversity is in full scale retreat. So any discussions of ‘optimal temperatures’ are clearly way off the mark. They miss the point entirely. Species and genetically-distinct populations are locally adapted to conditions which fall within well-defined thermal windows, and if conditions are pushed well outside of those windows at the current rate at which they are, then there will be many losers and few winners.

    On top of ‘longer-term’ warming (I use quotations here because even the longer term rate of warming is probably unprecedented for most species found today) are, of course, climatic extremes, that are an even greater threat, because they hammer populations over short time-scales. These extremes are increasing in frequency, duration and intensity. Ectotherms, such as arthropods, are especially susceptible to extreme heat; we already know that upper lethal limits for some insect species is higher than upper thermal limits for their reproduction. In other words, some species can survive temporary heat exposure but it can destroy their eggs and/or sperm, making it impossible for them to reproduce. This turns them into ‘the living dead’. Some of my current research examines the effects of heat exposure on development, survival and reproduction in spiders.

    The bottom line is that climate change and climatic extremes represent a huge and unpredictable experiment on biodiversity and complex adaptive systems. These systems generate conditions that permit humans to exist and persist. This experiment cannot really be replicated, so it is an enormous gamble. Given our dependence on natural systems, and on knowing that previous mass extinctions were caused by rapid surface warming, it seems bizarre for me to read threads where people are attempting to defend climate change by claiming that ‘warmth is better’ without placing this into the proper context. Warmth is not ‘better’ at all when it is generated over just several human generations.

  56. Willard says:

    > The biosphere is warming more rapidly than in hundreds of thousands of years and perhaps many millions of years.

    Thanks, Jeff. I added that line to my “But Life” square:

    “But Life”

  57. mrkenfabian says:

    “The bottom line is that climate change and climatic extremes represent a huge and unpredictable experiment on biodiversity and complex adaptive systems. ”

    Welcome to the test tube. Despite the near absolute certainty when the experiment runs it’s course the use of computer modeling is looking like a MUCH better alternative. Although even real world evidence is likely to continue to be disputed, up to and beyond the catastrophic.

  58. Dave_Geologist says:

    As I recall it’s generally thought that we’re warming about a hundred times as fast as the End Permian, but ten times as fast as the PETM. My favoured explanation for the speed of the PETM is the Antarctic permafrost one. Antarctica was a huge plateau and as warmth rose up the sides melting was slow, bit by bit. When it reached the plateau, it all went as once (limited only by the latent heat of melting). The Siberian tundra is like that. Flat, all at the same latitude, all exposed to the same warming. The original driver probably was the burning and vaporisation of hydrocarbons during North Atlantic rifting. Carbon cycle instability had started 1.5 m.y. earlier: Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum. There’s one lone wolf that says about the same speed as the PETM, but that relies on a very controversial interpretation of some shelf sediments off the east coast of America, that the cycles are annual and daily. That’s normal in lakes but offshore they’re more like decadal (oscillations like El Nino or the AMO) and fortnightly (the passage of successive storms).

    The enhanced hydrological cycle will hit us first – it already is with record droughts and floods. The PETM was that on steroids. Multi-year not multi-month droughts, torrential downpours once a decade, car-sized boulders rolled hundreds of kilometres across Spain. Good luck making agriculture work amidst that. So much clay was washed into the oceans that there was a global change in the mineralogy of ocean-floor sediments. The North Sea was a toxic soup, like those bloom-affected lakes you’re warned to stay clear of. We see it in the rocks (the Sele Formation). Ironically it makes them hard to drill though and keep stable. They’re fissile because unlike the rocks above and below they’re not bioturbated. Because there was no bio down there to turbate. And unlike the euxinic lake-floor sediments of the Devonian Orcadian Lake, not full of fish bones and scales. Presumably no fish. Greening of the Sinai, yes, but desertification of other areas.

    Or we could take action to prevent that happening.

  59. russellseitz says:

    Willard :
    “Appeals to alarmism or alarmists often act as hyperbole or caricature. Identifying the target of the concern is key. “…

    If Climate Desk has a sense of irony, let alone the sardonic, , it would insist on a clean, well lighted table overlooking Bingo Square.

  60. angech says:

    Steven Mosher
    “What is the optimal temperature for life on earth?
    What is the optimal level for CO2 levels on earth?”

    “There is no optimal temperature for life on earth. no single temp that will optimize some aspect of life. nevertheless we know -5C would be a bad thing. and 50C would be a bad thing. we know ranges and risks with extremes.
    14C has been pretty good for us. if it aint broke!!”

    Steven,thank you for your answer, the first real attempt by anyone to address this question sensibly.
    Salient points you make.
    There is a range of temperatures that suit different life forms differently.
    Too cold -5C, or too hot 50C would be bad for most life forms that we recognize.
    We have a good idea of the ranges, risks and extremes.
    We also know that life has already adapted in the past to periods of cold,
    more recently and heat before that and that our current forms are different to that of more ancestral life when it was not 14C.
    There is nothing special about 14 C, the only reason you can say it is good for us is that we are currently surviving in a range in which the median in some parts of the world is 14C.

    The use of the word optimal is deliberate.
    It has a meaning that everyone understands even if no-one can agree on exactly where it is.
    When we speak of temperature we can all, as you have done express an estimate centered on the middle of the range we would like to live in.
    Life similarly is understood by all as is the earth.
    14C is lovely as an average for the globe generally but allows the spread of temperatures seasonally plus day and night that we all enjoy.
    I would go a little higher, seeing that more life was present on the earth in warmer millenia at least 2C warmer than the IPCC baseline , say 16 C?

    We are all able to call an optimal temperature and have others disagree with us but you and I would certainly be in the same ball park on this one.
    I would like to state that just because the IPCC works from a baseline of 14C and you happen to like it does not mean it is the optimal temperature for many reasons. Fear of change of the status quo by many [not on your part], or pushing one temperature as ideal because we can then fear departing from it are reasons for favouring 14 C.
    But what are the benefits of change and what should the science say when pressed to justify this choice.?

    i asked my doctors for my optimal weight
    they gave me a range not less than X not more than Y
    they said 200lbs was not good but didnt give an optimal. they gave an average
    and danger levels

    they said i was at increased risk, but because they couldnt say 187.78 lbs exactly
    i pretty much ignored them. asking for optimal is not a good idea. if you’re going to ignore
    the answers science can give you.

    for most life on earth earth we might say not less than 0C not more than 35C
    14C has been pretty good for us. if it aint broke!!
    Steven Mosher says:
    August 11, 2021 at 11:57 am

    Angech is their an optimal time for you to leave for work in the morning

  61. Jeffh says:

    Angech, let me respond to your rather simple post. I thought that I had pretty well debunked the arguments your are making in my first response (above), but clearly either you did not read it or understand it. I can partially understand your reticence to understand the scientific facts, given your contrarian leanings. Still, it annoys me when I see non-environmental scientists attempting to put a positive spin on anthropogenic warming by suggesting that much of biodiversity thrives at higher temperatures so therefore the human amplification of global temperature must be a good thing.

    Nothing could be farther from the truth. As someone qualified to comment on this issue, I wish to strongly reiterate that it is not mean surface temperature that matters so much as the temporal rate of change. Yes, nature does ‘better’ at warmer temperatures to a point, but what is much more important is predictability and stability. Temperate species are adapted to seasonal changes in temperature and photoperiod whereas tropical species are better adapted to low variability in both of these parameters. By causing the biosphere to warm at rates unseen in hundreds of thousands or many millions of years, we are forcing nature – ecosystems, communities, trophic interactions, species and populations – to adapt well outside of their thermal optima. Given enough time – many thousands of years at least – many species and biomes could adapt. But the current rate of warming globally and even more locally falls well outside of the ability of much of biodiversity to respond adaptively, and an increase in exposure to extreme events like heatwaves is making the situation worse. As I explained above, many ectotherms are being exposed to extreme temperatures at or above the upper thermal limit for reproduction and/or survival. The deleteriois effects of these thermal stresses are being amplified by a range of other anthropogenic stresses. Nature is already responding as much as it can to the rate of warming thus far – we are seeing range shifts polewards or to higher elevations, changes in seasonal or diel activity patterns, changes in voltanism, and other physiological forms of local adaptation. But this is not nearly enough to cope with an unprecedented rate of warming combined with threats posed by other human-mediated stresses.

    So, once again, discussions of ‘optimal temperatures’ for biodiversity are pointless because they ignore scale.

  62. Willard says:

    > the first real attempt by anyone to address this question sensibly.

    I resemble that remark, Doc`

    Ron,

    I’m glad we both agree that we need to get to Carbon Zero ASAP.

    Once we agree on that, there is no need to pussyfoot about the optimal level of CO2 in the atmosphere.

    Even Doc should be able to see that. Suppose he offers you to play Russian roulette. The only reason why you’d bother to calculate the odds would be if you’d accept. Once you refuse to play, no need to determine optimal strategy.

    Same for CO2 levels.

    Doc’s riddle only matters to those who feel lucky.

    Those who, like you and me, want to get to Carbon Zero ASAP don’t need to answer it.

    https://judithcurry.com/2021/08/09/ipcc-ar6-wg1-discussion-thread/#comment-957400

  63. Eabani says:

    ‘What does seem to have changed is there seem to be stronger statements about extreme events’

    The SPM presumably didn’t have room for a ‘what’s new’ section, but the Technical Summary has such a thing near the front, comparing to AR5 WG1 and the special reports SR15, SRCCL and SROCC (the ‘technical’ summary is not nearly as soporific as you might think, although the available draft PDF hasn’t inserted many of the graphics into position and some don’r render easily). AR6 WG1 acknowledges some of the ‘low-likelihood high-impact’ events including Marine Ice Cliff Instability and AMOC shutdown, without great emphasis, but still feels like a step forward. The particular change I noticed over two years since SROCC is the increased rate of ocean acidifcation and stratification, which may have knock-on effects for the ocean as a carbon sink and particularly marine biodiversity. Jeffh is wise in my opinion to search for geological precedents: the report compares current temperatures to the Eeemian, current atmospheric composition to the Pliocene, and potential change to the Eocene. Dan Rothman at MIT has suggested the speed of change could cause a millennial ocean tipping point, not something we were envisaging among climate concerns in the 1950s.

    In terms of stronger statements, the TS uses ‘established fact’ twice, in reasonable English usage. ‘Human influence on the climate system is now an established fact’ and:

    Chapter 11 ‘concludes that it is now an established fact that human-induced greenhouse gas emissions have led to an increased frequency and/or intensity of some weather and climate extremes since 1850, in particular for temperature extremes. Evidence of observed changes and attribution to human influence has strengthened for several types of extremes since AR5, in particular for extreme precipitation, droughts, tropical cyclones and compound extremes (including fire weather).’

    Fire weather, flooding and drought using high-resolution regional climate models are projected at a regional level. This and the new atlas should be really useful for planning adaptation and there’s of course much more to come in WG2 in February.

    The effect of the narrowing TCRE is that the 67% remaining carbon budgets haven’t reduced much compared to the 33% ones. The biggest shift is focus on the SSP1-1.9 pathway, which (even if greenhouse gas removals scale up in future decades) requires rapid demise of fossil fuel extraction. Lead authors were in the UK media saying 5% a year, slightly slower than the UN Production Gap report.

  64. angech says:

    Thanks to all for the comments above.

    I just got round to seeing them yesterday and this morning but I sincerely appreciate ATTP/Willard putting them up and the interest it has generated.
    I have to make an answer to Joshua and try to get Willard to answer the question though it seems he feels it is not needed.
    We are in lockdown but I am supposed to go out on work with an exemption today.
    When I have sorted that out I will try to get back tonight and make some sensible comments
    [I know].

    I do feel very strongly that if you want to avoid emission rise and warming you have a responsibility to state what and why the temperature level you are concerned about is the right one.
    This is a very complex question and at the heart of a lot of my skepticism, apart from my built in contrarianism which masks true skepticism all the harder.

    Thanks to Steven Mosher who is the only one so far to give a genuine answer to this complex question and has an extra understanding of how hard it is to get a true world temperature base.

    The frog in the hot water analogy is supposed to show how we can get into trouble with rising temperatures.
    I prefer to think of it as evolution at work.
    Perhaps we get a live hot frog adapted to hot springs rather than a cooked one?

  65. angech says:

    Joshua says:
    “What reason other than calling people “alarmist, ” as a way of demonizing those you disagree with, do you have for existing?”
    Firstly I do not demonise those I disagree with.
    Your perception that calling people alarmist is demonising is instructive, look at it closely, explain.
    The first and most important one [meaning of life] [existing] is to be helpful to other people.
    After the laughing and floor rolling this is still my view.
    I may disagree with people, agreed? I may describe their viewpoints, agreed? None of this constitutes demonisation.

  66. Jeffh says:

    Again, Angech, your replies are essentially disposable. I really do not wish to waste more of my time on them.

    Evolution takes time. Much more time than the current atmospheric experiment is giving it. The current rate of global surface warming exceeds that which precipitated previous mass extinctions by several times. On top of that are a range of other anthropogenic threats which amplify the harmful effects of warming. We will not see many live frogs adapted to hot springs, to use your analogy. We are going to see a mass of dead, boiled ones. Homo sapiens will be among the more prominent victims.

    Your understanding of the relevant science is poor, and it is this which underpins your contrarianism. I will leave it at that.

  67. Joshua says:

    angech –

    > Your perception that calling people alarmist is demonising is instructive,..

    It’s tribal. Pejorative. It’s in bad faith. It’s insulting. It disdables good faith exchange. It’s playing the player, not the ball. It’s like me calling you a “denier,” which necessarily is a sign of bad faith exchange.

    > I may disagree with people, agreed?

    Name-calling isn’t signaling disagreement. It moves from discussion of point of view to expressing personal antipathy.

    > I may describe their viewpoints, agreed?

    What? Calling someone “alarmist” is describing their viewpoint? Only a denier could write something like that. (But I’m not being demonizing).

    .

  68. Willard says:

    > I do feel very strongly

    Feeling strongly isn’t exactly an argument, Doc. It does not counter mine. It is pure contradiction.

    And you repeated it many times already. I suggest this stops.

  69. angech says:

    I am having a discussion with em Ellison regarding whether the faster a planet spins the higher its average temperature should get [closer] to the ideal average temperature. A post at Roy’s agrees with my view that it does increase but the other argument is energy in, energy out a previous favorite of mine.
    No google help. No other sources.
    Does ATTP have an opinion, his field, or would someone else DG etc be able to help out with a reference to set me straight?

    Thanks.

  70. angech,
    I can’t see why the rotation rate would influence the average temperature (at least as measured by energy balance). However, a fast rotating planet can distribute energy differently to one that, for example, is synchronously rotating.

  71. angech says:

    Thanks.
    There are a couple of these problems that are out there.
    This is the only one worth bothering you about as it is in your field.
    I will go away and think about it some more.

  72. Dave_Geologist says:

    angech, there are a number of differences rotation rate makes, from the distribution of temperature to the presence or absence of a strong magnetic field. Which influences all sorts of things. It’s complicated. That why we need finite-difference models.

    It feeds in a little bit to energy balance, because a 1°C temperature rise has different outgoing-radiation-change implications in a hot place vs. a cold place. It moves ΔT around the planet non-linearly. That’s part of the reason a global-average model like Lewis & Curry’s is garbage-in, garbage out. It’s what everyone did before they could do better, but now the data and computer resources are there to do better, people do better and understand why it gives an unreliable result for forward prediction.

    Changed Coriolis forces will change ocean currents and wind/storm/cloud distribution in complicated ways, which can also feed into energy balance. Of course the Earth’s rotation rate is changing so slowly that it’s immaterial on a human lifetime, indeed on the timescale of humanity’s residence on Earth. It is of interest for the early Earth, for the other planets, and for exoplanets.

    The sustainability of habitability on terrestrial planets: Insights, questions, and needed measurements from Mars for understanding the evolution of Earth-like worlds

    The Role of the Nonlinearity of the Stefan–Boltzmann Law on the Structure of Radiatively Forced Temperature Change

  73. As far as the Earth’s rotation rate, it is what it is, and hypothesizing on what would happen if it differed substantially is not that useful. More useful is to understand the cause of the variation in the current rate, which is usually discussed via tracking the length of day (LOD) deviations. Up to the annual cycle, about 99% of the variations are due to the solar and lunar tidal cycles applying a torque (either directly or indirectly) to the earth’s moment of inertia. Amazing the precision of this model, as even the 18.6 year lunar nodal modulation is observed.

    Beyond that it gets more fuzzy, with the interesting correlation of multidecadal average global temperature changes aligning fairly well with the multidecadal LOD variation. A former NASA JPL scientist has been working on this for years and has apparently kept up with the correlation studies with this paper from 2016 “Does an Intrinsic Source Generate a Shared Low-Frequency Signature in Earth’s Climate and Rotation Rate?” https://journals.ametsoc.org/view/journals/eint/20/4/ei-d-15-0014.1.xml. See Figure 3 in particular. It’s possible that this too is a tidal torque effect but its nonlinear and acting on the ocean volume.

  74. angech says:

    Thanks, DaveG,
    angech, there are a number of differences rotation rate makes, from the distribution of temperature to the presence or absence of a strong magnetic field.
    thanks Paul.
    Up to the annual cycle, about 99% of the variations are due to the solar and lunar tidal cycles applying a torque (either directly or indirectly) to the earth’s moment of inertia
    Both insights helpful.
    appreciated. +++

  75. verytallguy says:

    Angec.

    A thought experiment may help.

    Consider an atmosphereless planet, and the following two limiting cases.

    Scenario 1: rotation rate exactly tidally locked. Sun facing side is in radiative balance with incoming. Reverse side is at absolute zero.

    Scenario 2: rotation rate infinite. Entire planet is at same temperature, in radiative balance with incoming.

    In Scenario 1, the mean surface temperature is lower than Scenario 2, because the SB law goes with the 4th power of T. Its Sun facing surface radiates at twice the rate of the planet in Scenario 2, but the temperature on that side is only above the average temperature in Scenario 2 by the 4th root of 2 (1.189).

    [This treats the planet as planar rather than spherical, but the principle is still hopefully clear]

    There’s a real world example: Mercury. Not precisely tidally locked, but the temperatures in either side are quoted as 100 to 700K (WIKI)

  76. Just to follow up a bit on VTG’s comment. There is a difference between what you’d get if you determined the effective radiative temperature and the average of the temperature. The former should not depend on the rotation rate of the planet (it depends on energy in = energy out), while the latter will depend on the rotation rate of the planet. As VTG points out, a synchronously rotating planet will have a different average temperature to a rapidly rotating planet even if they have the same effective radiative temperature.

  77. Dave_Geologist says:

    Appreciation appreciated, angech,

    The spinning vs. tidally locked scenario is an extreme version of the terrestrial energy-balance one, where you get a better answer if you sector by latitude, low-mid-high, to account for Arctic amplification of warming.

    By coincidence, I recently came across this paper picking apart the short and long term causes of Arctic amplification (paywalled but you can find copies on Google Scholar).

    .Arctic Amplification: A Rapid Response to Radiative Forcing

  78. Dave_Geologist says:

    Thanks, ATTP.

  79. Mal Adapted says:

    Dave_Geologist, thanks for that link. I recently saw a couple of claims that Antarctic sea ice growth somehow balances Arctic sea ice loss, and countered with Arctic amplification. I’ll be even better prepared now 8^D. I find the $50/yr for an AGU membership well worth it, when confronting ClimateBall players!

  80. angech says:

    Hmm. I would like to use both those arguments of verytallguy and ATTP at Judith’s blog to try to convince someone that while the energy out is constant the temperature averaged might change with rotation rate.
    Hoping that is OK.
    Might get heated so I will deidentify it.

  81. Willard says:

    That someone might be you, Doc:

    The Faster a Planet Rotates, the Warmer its Average Temperature
    September 28th, 2016 by Roy W. Spencer, Ph. D.
    This is a followup to my post from yesterday where I provided time-dependent model results of the day-night cycle in lunar temperatures.

    https://www.drroyspencer.com/2021/08/uah-global-temperature-update-for-july-2021-0-20-deg-c/#comment-781422

    Here’s what Roy says:

    Basically, any process which increases the day-night temperature range (such as a longer diurnal cycle) will decrease the average temperature of a planet, simply because of the non-linearity of the S-B equation. I suspect the effect does not exist if the surface being heated has zero heat capacity, since the temperature of the surface will instantly come into equilibrium with the absorbed sunlight; in that case the length of day would not matter. But since that is physically impossible, it does not apply to real planets.

    https://www.drroyspencer.com/2016/09/the-faster-a-planet-rotates-the-warmer-its-average-temperature/

  82. I think one should stress that there is a difference between effective radiative temperature, which depends only on energy balance (i.e., energy in = energy out) and the average of the temperature, which will depend on how the temperature is distributed across the surface. Essentially, given the T^4 dependence for energy radiated into space, means that if you have two planets with the same incoming energy, the average of the temperature of the planet with a large temperature difference between the two hemispheres will be smaller than the average of the temperature of planet where the hemispheres have similar temperatures. However, the effective radiative temperatures will be the same.

  83. angech says:

    Willard says: September 13, 2021 at 4:26 pm “That someone might be you, Doc:”
    No, I don’t think so.
    That excerpt was for people to look up at that site and refer to.
    It was the opening sentence of Spencer’s article, not something I had done.
    Poorly parsed on my part.

    For my part I am happy to see the general agreement between the scientists on this issue as ATTP has reinforced.
    He has again put it very clearly with the gravitas I lack.
    Does feel strange to all be on the same side for one of those sliding door moments.
    At least one of my concepts matches, 99 to go.
    .

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