o.k., well-taken -- I just wanted to make the point that, if you start out accepting IPCC's best estimate for aerosol forcing, there is a human tendency, given the choice of many models/parameters, to choose the model/parameters that yield realistic global warming -- and this is a way to "bake in" the ECS (3C for doubled CO2) that agrees with the assumed (IPCC) aerosol forcing. Jim
On Mon, May 19, 2025 at 8:20 PM Michael MacCracken <[email protected]> wrote: > Hi Jim--No need for a back and forth. I did not mean to dismiss your > calculation of sensitivity possibly being 4.5 C and don't disagree that the > set of parameters used in models now do tend toward yielding a 3 C > sensitivity. Indeed, I found your latest results very interesting, high as > the sensitivity seems if one goes back to when the CO2 concentration is > thought to be 4 or more times preindustrial. > > In my interactions with Ron and others, I was interpreting their remarks > to be saying that the climate sensitivity was directly specified as 3 C in > the models independent of how the processes work and come together, and I > wanted to say that that is not the case. At least that was what I was > intending to say. I should perhaps have made more clear your point that > some of the parameters in the existing model should, based on the time > history of observations and seeking to match the model results to them > could well be indicating that different parameters regarding cloud feedback > are likely the case and this could lead to the higher sensitivity and > improved the match to the multiple types of observations that you consider. > > Good luck for your move back to New York City. > > Best, Mike > On 5/19/25 8:00 PM, James Hansen wrote: > > Hi Mike et al., > > I can't get involved in a back-and-forth -- we are in the process of > moving back to NYC, to live in a Columbia apartment to avoid time wasted in > commuting and taking care of a house/property. However, I'm surprised by > your comment, Mike. Most GCM groups make hundreds, if not more, GCM runs > between one IPCC report and the next, and there are hundreds, if not more, > model parameters. There is a widespread, if not universal, tendency to > prefer those model configurations that yield a magnitude of warming in the > past 200 years that is consistent with observations. In this way, wittingly > or not, the 3C sensitivity is "baked into" the models -- because, as we > showed in our "Acceleration" the usual aerosol forcing employed is close to > the IPCC best estimate for aerosol forcing. As shown by a graph in the > Supplementary Information of our paper, the change of the IPCC aerosol > forcing during the period of rapid warming is negligible. In such case, the > climate sensitivity required to match the observed warming rate is ~3C for > 2xCO2. However, if the aerosol forcing increased by ~0.5 W/m2 (became more > negative) during 1970-2005, as simulated by Bauer et al. and as > independently inferred in our paper, then a climate sensitivity of ~4.5C is > required to match the observed warming. > > However, the temperature change in the last 200 years is only one of the > three independent ways that we obtain the 4.5C sensitivity, and the other > two are much cleaner, independent of the GCM issues. > > High climate sensitivity demanded by large cloud feedback, clearly shown > by Earth's darkening in the past 25 years, is summarized in the recent > communication to my email list. > > The third method is described in our "Global warming in the pipeline" > paper: comparison of equilibrium glacial and interglacial climates. For > several decades, based largely on CLIMAP and "confirmed" by MARGO, it was > believed that the LGM was only 3-4C colder than the Holocene. Thanks > especially to Alan Seltzer, we now know that the LGM was 6-7C colder, which > demands the higher ECS -- several new paleo studies confirm the high ECS. > > Best, Jim > > On Mon, May 19, 2025 at 3:39 PM 'Michael MacCracken' via geoengineering < > [email protected]> wrote: > >> Ron et al.--Just a note that the 3 C sensitivity is not "embedded" in the >> climate models. That is the value that emerges from the representations of >> the various physical processes that play out against each other. So, >> assuming the observations and resulting analyses are accurate, for there to >> be a higher sensitivity, it might be that some of the processes are not >> parameterized in a way that fully represents possibilities and realities >> (observations to calibrate parameterizations can be drawn from only the >> conditions we are experiencing), some processes are not represented at >> all (viewed as long-term such as isostatic rebound, etc.), the resolution >> of the models is not fine enough to treat aspects of the processes, etc. In >> any case, however, the 3 C sensitivity is not built into the models. >> >> Mike >> On 5/19/25 1:49 PM, Ron Baiman wrote: >> >> Thank you LDM and Dan, >> >> @LDM: >> >> (IMO) Thanks for sharing! IMO this recent Hansen and Kharecha Newsletter >> with further evidence supporting a climate sensitivity of 4.5 rather than >> the established IPCC value of 3.0 that is (as I understand it) embedded in >> most current climate models, is excellent and should be widely distributed, >> per these last two paragraphs: >> >> "Criticisms of the Acceleration paper in the media did not address the >> physics in our three assessments of >> climate sensitivity. Instead, criticisms were largely ad hoc opinions, >> even ad hominem attacks. How can >> science reporting have descended to this level? Climate science is now so >> complex, with many sub- >> disciplines, that the media must rely on opinions of climate experts. >> Although there are thousands of >> capable scientists in these disciplines, the media have come to depend on >> a handful of scientists, a clique >> of climate scientists who are willing, or even eager, to be the voice of >> the climate science community. >> But are they representative of the total community, of capable scientists >> who focus on climate science? >> We have lamented9 the absence of scientists with the breadth of >> understanding of say Jule Charney or >> Francis Bretherton,10 or our beloved, sometimes crotchety, former >> colleague, Wally Broecker. However, >> the truth is that there are many scientists out there with a depth of >> understanding at least as great as the >> clique of scientists that the media rely on. Given the success of this >> clique in painting us as outliers, we >> are dependent on the larger community being willing to help educate the >> media about the current climate >> situation. For that purpose, we will discuss – one-by-one in upcoming >> communications – several of the >> matters that are raised in our papers. Thanks for your attention." >> >> @Dan: Thanks for sharing! I will definitely give this a listen! >> >> Best, >> Ron >> >> >> On Sun, May 18, 2025 at 4:04 PM LDM <[email protected]> wrote: >> >>> >>> https://www.columbia.edu/~jeh1/mailings/2025/CloudFeedback.13May2025.pdf >>> >>> Large Cloud Feedback Confirms High Climate Sensitivity >>> James Hansen and Pushker Kharecha >>> 13 May 2025 >>> >>> Abstract. >>> >>> Earth’s albedo (reflectivity) declined over the 25 years of precise >>> satellite data, with the decline so large that this change must be mainly >>> reduced reflection of sunlight by clouds. Part of the cloud change is >>> caused by reduction of human-made atmospheric aerosols, which act as >>> condensation nuclei for cloud formation, but most of the cloud change is >>> cloud feedback that occurs with global warming. The observed albedo change >>> proves that clouds provide a large, amplifying, climate feedback. This >>> large cloud feedback confirms high climate sensitivity, consistent with >>> paleoclimate data and with the rate of global warming in the past century. >>> >>> >>> https://youtu.be/NxV1IbHt7fU >>> >>> When Will We Go Over 2ºC? & Hansen's Cloud Update >>> <https://www.youtube.com/@climatechat> >>> >>> >>> On Sun, May 18, 2025 at 9:09 PM Ron Baiman <[email protected]> wrote: >>> >>>> Wow! Thanks for sharing Renaud. I haven't read it but from the >>>> abstract it (very unfortunate for all of us humans and most other species, >>>> but not really surprising for many of us humans) looks like forecasts of >>>> Hansen et al. 2024 are being vindicated! >>>> Best, >>>> Ron >>>> >>>> >>>> On Wed, May 14, 2025 at 9:51 AM Renaud de RICHTER < >>>> [email protected]> wrote: >>>> >>>>> Earth's Energy Imbalance More Than Doubled in Recent Decades >>>>> https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024AV001636 >>>>> Abstract >>>>> >>>>> Global warming results from anthropogenic greenhouse gas emissions >>>>> which upset the delicate balance between the incoming sunlight, and the >>>>> reflected and emitted radiation from Earth. The imbalance leads to energy >>>>> accumulation in the atmosphere, oceans and land, and melting of the >>>>> cryosphere, resulting in increasing temperatures, rising sea levels, and >>>>> more extreme weather around the globe. Despite the fundamental role of the >>>>> energy imbalance in regulating the climate system, as known to humanity >>>>> for >>>>> more than two centuries, our capacity to observe it is rapidly >>>>> deteriorating as satellites are being decommissioned. >>>>> Key Points >>>>> >>>>> >>>>> - >>>>> >>>>> Earth's energy imbalance more than doubled in recent decades >>>>> - >>>>> >>>>> The large trend has taken us by surprise, and as a community we >>>>> should strive to understand the underlying causes >>>>> - >>>>> >>>>> Our capability to observe the Earth's energy imbalance and budget >>>>> terms is threatened as satellites are decommissioned >>>>> >>>>> Plain Language Summary >>>>> >>>>> Global warming is caused by the imbalance between the incoming >>>>> radiation from the Sun and the reflected and outgoing infrared radiation >>>>> from the Earth. The imbalance leads to energy accumulation in the >>>>> atmosphere, oceans and land, and melting of the cryosphere, resulting in >>>>> increasing temperatures, rising sea levels, and more extreme weather >>>>> around >>>>> the globe according the the United Nations Intergovernmental Panel on >>>>> Climate Change (IPCC). Observations from space of the energy imbalance >>>>> shows that it is rising much faster than expected, and in 2023 it reached >>>>> values two times higher than the best estimate from IPCC. We argue that we >>>>> must strive to better understand this fundamental change in Earth's >>>>> climate >>>>> state, and ensure our capacity to monitor it in the future. >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Healthy Planet Action Coalition (HPAC)" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to >>>>> [email protected]. >>>>> To view this discussion visit >>>>> https://groups.google.com/d/msgid/healthy-planet-action-coalition/CAHodn9-e2iCfiPJYDRnv2TTcjgCueetUw9Fs83Tp48B2gA0jJA%40mail.gmail.com >>>>> <https://groups.google.com/d/msgid/healthy-planet-action-coalition/CAHodn9-e2iCfiPJYDRnv2TTcjgCueetUw9Fs83Tp48B2gA0jJA%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> >>>> >>>> -- >>>> Healthy Planet Action Coalition <http://www.healthyplanetaction.org> >>>> YouTube Channel >>>> <https://www.youtube.com/channel/UCdt5vatByfyg-Pm9Vu6ahZg> >>>> @HPACoalition (Bluesky and Twitter/X) >>>> Addressing the Urgent Need for Direct Climate Cooling: Rationale and >>>> Options <https://academic.oup.com/oocc/article/4/1/kgae014/7731760> >>>> Baiman et al. 2024. *Oxford Open Climate Change* >>>> An Open Letter to the IMO Supporting Maritime Transport that Cools the >>>> Atmosphere While Preserving Air Quality Benefits >>>> <https://academic.oup.com/oocc/article/4/1/kgae008/7706251>. Baiman et >>>> al. 2024. *Oxford Open Climate Change* >>>> >>> >> >> -- >> Healthy Planet Action Coalition <http://www.healthyplanetaction.org> >> YouTube Channel >> <https://www.youtube.com/channel/UCdt5vatByfyg-Pm9Vu6ahZg> >> @HPACoalition (Bluesky and Twitter/X) >> Addressing the Urgent Need for Direct Climate Cooling: Rationale and >> Options <https://academic.oup.com/oocc/article/4/1/kgae014/7731760> >> Baiman et al. 2024. *Oxford Open Climate Change* >> An Open Letter to the IMO Supporting Maritime Transport that Cools the >> Atmosphere While Preserving Air Quality Benefits >> <https://academic.oup.com/oocc/article/4/1/kgae008/7706251>. Baiman et >> al. 2024. *Oxford Open Climate Change* >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion visit >> https://groups.google.com/d/msgid/geoengineering/CAPhUB9CnQHnNxxw0m238XK9mxSatsHedxndUf7vO0KoQkVeiXQ%40mail.gmail.com >> <https://groups.google.com/d/msgid/geoengineering/CAPhUB9CnQHnNxxw0m238XK9mxSatsHedxndUf7vO0KoQkVeiXQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion visit >> https://groups.google.com/d/msgid/geoengineering/4e23a031-1d90-429f-b962-a428e82fc7ac%40comcast.net >> <https://groups.google.com/d/msgid/geoengineering/4e23a031-1d90-429f-b962-a428e82fc7ac%40comcast.net?utm_medium=email&utm_source=footer> >> . >> > > > -- > Jim Hansen, Director > Climate Science, Awareness and Solutions Program > Columbia University Earth Institute > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/geoengineering/CAEL%2B3vM1eBgxrNdGNjtUOKv75kMx43UgfVnEu-T06SL7wOhYDQ%40mail.gmail.com > <https://groups.google.com/d/msgid/geoengineering/CAEL%2B3vM1eBgxrNdGNjtUOKv75kMx43UgfVnEu-T06SL7wOhYDQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > -- Jim Hansen, Director Climate Science, Awareness and Solutions Program Columbia University Earth Institute -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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