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.
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
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.
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https://www.columbia.edu/~jeh1/mailings/2025/CloudFeedback.13May2025.pdfLarge Cloud Feedback Confirms High Climate SensitivityJames Hansen and Pushker Kharecha13 May 2025Abstract.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.
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
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The variation is the result of people making the same mistakes in oversimplifying the major climate feedbacks, some oversimplify more than others for conceptual or technical reasons. The minimum value is the core GHG in all models, and from then on up is anyone’s guess, except that the models seriously underestimate the actual temperature sensitivity seen in paleoclimates. Hansen does a better job on the feedbacks than most!
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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
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
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Columbia University Earth InstituteJim Hansen, DirectorClimate Science, Awareness and Solutions Program
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On May 19, 2025, at 8:39 PM, James Hansen <jimeh...@gmail.com> wrote:
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
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Glacial-Interglacial changes and climate sensitivity:
CLIMAP’s temperature proxies based on foraminiferal assemblages (Imbrie et al.) claimed a much small glacial inter-glacial temperature range as that from O-18 (Emiliani, Shackleton), largely because equatorial foram populations stayed the same, although squeezed tighter latitudinally.
CLIMAP’s interpretation was therefore that there was almost NO large temperature decrease in the tropics even though all the tropical mountain lake palynology showed clear cooling of more like 10 degrees C!
For many wrong reasons, CLIMAP’s very low climate sensitivity interpretation became accepted as a de facto standard by the modeling community, despite most of the paleontological data which pointed to a much higher sensitivity than the models, clearly pointed out in 1990 after the very first IPCC projections.
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Geotherapy: Regenerating ecosystem services to reverse climate change
No one can change the past, everybody can change the future
It’s much later than we think, especially if we don’t think
Those with their heads in the sand will see the light when global warming and sea level rise wash the beach away
“When you run to the rocks, the rocks will be melting, when you run to the sea, the sea will be boiling”, Peter Tosh, Jamaica’s greatest song writer
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Agreed.
Mike
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 <mmac...@comcast.net> wrote:
Global Warming➔Fewer Clouds➔More Warming! with George Tselioudis
https://youtube.com/live/suFZb2ViHoA
ARSVR involves both solar radiation and thermal radiation to exert a cooling influence. Additional co-benefits can include run-off and erosion reduction, flood protection, carbon drawdown and sequestration, and promotion of increased biodiversity [104, 105]. There is some tension between the need for agricultural land versus. afforestation considering the increasing demand for food and impacts on local economies. Implementation would best aim for a complementarity achieved through a global land stewardship approach that balances need while maximizing benefits of afforestation, reforestation, regenerative agriculture, and agroforestry [102, 106]."
Jim,I still argue water vapour 51% (62% no clouds ) and 19% ( 25%) contributes to IR warming and co2 increases now no longer dominate the rises. With es(T) at 7% for each degree rise in surface air temperatures, then by 2-3 C rise gives a huge positive feedback , clouds or no clouds. A plot on a Elsaser diagram shows this. The radiative models don’t include it properly. Bignell’s water vapour continuum paper shows it works. Study of the planets mars and venus shows it.Thus in my opinion ECS is bigger than 5 ( may be 8) C. Look at the steepness of the current temperature curve increase. If ECS was say 4 the hysterisis would start to flatten off and it’s not.Thus I do think lovelock ( re verge of gaia, 2009) is correct , catastrophic weather events start by 2035 and martyn rees ( astronomer royal’s ) prediction for the end of the century are in the right ball park.Best wishesAlanT ---Alan Gadian, UK.Tel: +44 / 0 775 451 9009T ---On 20 May 2025, at 20:57, James Hansen <jimeh...@gmail.com> wrote:Thanks, Dan.It's a similar story with ECS implied by comparison of glacial and interglacial states.The forcings that maintain the glacial-interglacial temperature change are almost entirely:(1) Atmosphere: GHG change,(2) Surface: change of ice sheet sizeVegetation change also affects surface albedo, but it's a small effect and an estimate for it is included, even in our 1984 paper.Biology affects aerosols, but glacial-interglacial aerosol change is a climate feedback, part of the cloud-aerosol feedback (not a forcing); the biology effect is included in the empirical global temperature change.[Why is the biology effect (change of surface albedo due to change of vegetation distribution) included as a forcing, while the biology effect on aerosols is bookkept as a feedback? Because we have knowledge of the change of surface vegetation distribution, while the N aerosol types are unknown, especially their main effect, which would be via impact on clouds. So, the only choice is to leave it in the feedback category. These arbitrary forcing/feedback designations for vegetation and aerosols are small potatoes compared with GHG and ice sheet albedo changes.]Biology was sure a BFD in maintaining the fiction of 3C sensitivity for several decades. CLIMAP and MARGO estimated that LGM cooling was only about 3.6C based on their assumption that the microscopic marine biology would migrate to stay in the same temperature range where they exist today. Actual LGM cooling was almost a factor of two larger.Jim
On Tue, May 20, 2025 at 12:52 PM Dan Miller <d...@rodagroup.com> wrote:
Hi Herb:I read Dr. Mararieva’s comments and I don’t believe she understood Jim’s recent communication fully. I explain Jim’s latest communication it in my recent Climate Chat program. In a nutshell, the Earth dimmed by 0.5% in the past 25 years. There are 3 main causes: 1) Less sea ice, 2) changes to aerosols, and 3) could feedbacks. We know (1) well from direct observation. The IPCC thinks (2) is less than Jim does, but if that it true then (3) is even bigger than Jim says. The bottom line is that there are large cloud feedbacks (less clouds as the planet warms) which implies a large ECS (4.5ºC). See my interview with George Tselioudis for more on cloud feedback:
Global Warming➔Fewer Clouds➔More Warming! with George Tselioudis
https://youtube.com/live/suFZb2ViHoA
While biological processes of course play a role in climate change, it’s hard to see how a biological process played a role in changing the Earth’s albedo by 0.5% in the past 25 years, unless such process plays a major role in short-term cloud cover. Even if it did, it does not change Jim’s conclusions since he doesn’t say why the cloud feedback is so large, just that it is.Dan
Jim,I know that your time is short but if you have a few moments I’d love to get your response to Dr Anastassia Mararieva’s (who has a PhD in atmospheric physics and formulated the concept of the biotic pump ) article on Substack published today.She argues that the biosphere is neglected in both your work and the work of most mainstream climate modelers and scientists (I’m oversimplifying her argument of course but it touches on ECS, aerosols, clouds and much more.)Thanks,Herb
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----Columbia University Earth InstituteJim Hansen, DirectorClimate Science, Awareness and Solutions Program
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