As a rule climate outcomes tend to deliver results above, or well above, those predicted. Furthermore, today’s climate policy goals can no longer be relied on, in view of the mad stampede for Arctic oil and gas,combined with the oil industry’s successful defiance of all efforts to rein it in. Conservatively, the fossil fuels sector will kill 350m people by 2050 and over a billion by 2100, not including those who die of famine or water scarcity. Instead of attempting to predict degrees of heating, it is time the climate community got real and predicted human fatalities. Governments and corporates would find that less easy to ignore.
I started to say Julian's figures are in the ballpark, depending on the ballpark's dimensions. Then I realized I don't know where his numbers come from either. I'm familiar with some peer-reviewed estimates, e.g. https://www.nature.com/articles/s41467-023-41888-1:
"We find that US $143 billion per year of the costs of extreme events is attributable to climatic change. The majority (63%), of this is due to human loss of life."
"Across all study countries, we find that 37.0% (range 20.5–76.3%) of warm-season heat-related deaths can be attributed to anthropogenic climate change and that increased mortality is evident on every continent. "
I don't see total attributable mortality adding up to 350 million within 25 years, nor over a billion by 2100.
OTOH, we're almost certain anthropogenic global warming has already killed at least one person (e.g. https://www.nature.com/articles/s41467-023-36289-3). To suggest it won't kill more before the trend of GMST is capped, is simply perverse. How many attributable deaths do lukewarmers need before they'll support collective decarbonization?
It is a mistake to assume climate deaths are the main impact of fossil fuels, Health data indicates that deaths from various forms of fossil fuel poisoning are at least ten times greater than (current) climate deaths. However, because this is down to chemistry, science largely feels free to ignore it. So start here, noting that "environment" is a greenwash term for industrial and domestic poisoning: https://www.who.int/data/gho/data/themes/public-health-and-environment
I have a very long list of problems with the oil&gas industry, even before we get to greenhouse gas emissions. They play up how indispensable they are while they're undermining alternatives.
Ah. Thanks for engaging. You're right that climate deaths aren't the only impact of fossil fuels on human health and biodiversity. There is abundant science on air and water quality degradation, and other social and ecological costs of the market-driven transfer of geologic carbon to the atmosphere by the gigatonnes annually. Individual scientists are free to ignore much of it, and specialize on another topic of interest to them: otherwise, they'd have no time for deep understanding of any topic, chemistry included.
That said, Svante Arrhenius was a chemist. Prof. Dessler has atmospheric chemistry on his CV. But he and Dr. Hausfather are climate specialists. That's why we talk mostly about climate change here. It doesn't mean "science" is ignoring the total human and biodiversity costs of this manifold tragedy of the commons. For example, this blog's authors also talk about the "free" market's ancient propensity to socialize all the transaction cost it can get away with, hence the economic term "social cost of carbon". It's the underlying reason anybody talks about anthropogenic climate change: who pays for the SCC, and who benefits by socializing it?
So why focus on climate-change attributable mortality? While any death is a tragedy for the victim if no one else, those that wouldn't have occurred in a counterfactual world where adding fossil CO2 to the atmosphere doesn't increase global heat content, tend to draw the public's attention: especially when the public is sweating through yet another record-breaking heat wave, and at least some deaths are attributable to the additional heat of the enhanced "greenhouse" effect; or when record-breaking flash floods, cyclonic storm surges and winds kill scores or thousands, some fraction of whom would *almost certainly* - so certainly that it would be perverse to withhold provisional agreement, even without one specific number or other - still be alive if not for anthropogenic climate change.
Collective decarbonization advocates should of course be aware of the economic drivers of all socialized cost, not just human mortality, and also of the ways for-profit disinformers propagate greenwash along with simple denialism, as reviewed in "Disinformation as an obstructionist strategy in climate change mitigation: a review of the scientific literature for a systemic understanding of the phenomenon" (https://open-research-europe.ec.europa.eu/articles/4-169/v2). These anti-collectivist strategies and tactics were developed by the tobacco industry, for one, before global warming was on most of the public's mind.
Today there's a documented billion-dollar industry selling bespoke bullshit to anyone with the motivation and resources to pay for it. All of science is consequently ignored, or worse, distorted and politicized by carbon capital foremost, as it has the most profit to lose from collective intervention in the otherwise-"free" market. The more "lay" people who consider the source and follow the actual money, the better, IMHO.
Put simply, death statistics register with the public more than do 1 or 2 degrees Celsius, or atmospheric ppm. It’s simply a communication tool for explaining to the average person the likely cost of fossil fuels.
Based on Dr. James Hansen's recent work, a TCS of 4.5˚C seems more likely than the IPCC's estimate of 3˚C from a doubling of atmospheric CO2 concentration (youtube.com/watch?v=D2abyXGvELI).
If Hansen is right, none of the study estimates here are realistic. His long history of being right should give the IPCC reason to reconsider.
The important question is no longer so much of projected warming - we are in big trouble. The real question is when will the US will get around to closing the growing US carbon price gap with the prices of our major trading partners? Rather than dragging its feet, the US must help close the growing global carbon price gap: the global average price is $5/tCO2e, but the IPCC-recommended estimates required for a chance at a livable future is a global price of $80/tCO2e this year, rising to $135/tCO2e in 2030 and to $690/tCO2e in 2100 (carboncashback.org/carbon-price-gap).
I disagree with Hansen that 4.5C ECS is particularly likely (though it is within the uncertainty range). The same folks he relies on for paleoclimate data find a value of ~3C per doubling CO2 more or less in line with the central estimate: https://www.science.org/doi/10.1126/sciadv.adk9461
But the climate response remains quite uncertain; we should plan for a risk of 4.5C ECS in our policy response!
TY so much for your article. It's so good to know, as terrifying as it is. I'm curious, what does a 4.5C policy response look like? Would it be possible to respond at all within the chaos from that amount of warming?
Hansen may be old and wise, but he can still fool himself, which is why he submits his claims to non-sycophantic peer review. Hell, we could all use a little honest review by our "peers" before we make public claims! Zeke is helping to save us too, although maybe not the way you think he should. I'm guessing you're not their publishing peer, however.
I like Zeke toyourself. But, I take Hansen's word or knowledge over Zeke's.
Of course, don't blindly accept assertions. But, don't blindly refute when you know you are refuting someone with good will and much more experience than yourself.
Science is a collective enterprise, because you are the easiest person to fool. It's more important for non-experts to trust the consensus of experts, rather than any one expert. All experts, however, must respect the unsparing mutual discipline of their peers. In this case, the range of supportable ECS estimates leaves room for both Hansen and Hausfather, either until models converge more closely than they do currently, or until CO2 has actually doubled and we see how hot the globe actually gets.
No. The big point is there are many hundreds/thousands of scientists who would love to be a peer on one Jim's papers. Don't you climate parrots get it? Jim has been right and everybody wants to refute him. Call it climate envy.
People who aren't sufficiently exposed to the history, philosophy, culture, and practice of science, often have incorrect ideas about it. You're apparently one of them. No self-aware scientist is as sure of himself as you are. Knowledge, i.e. "justified true belief", is approached asymptotically and collectively, and proof is for mathematics and distilled beverages.
Besides, you lay zealots don't get it. Scientists who get their names on any published paper in a climate-science venue of record are "Jim's" ("Dr. Hansen's" to you) peers. They might love to be his co-author, but what they'd really love is to be first author on their own paper in *Science* or *Nature*. If Dr. Hansen's their co-author, so much the better, but they can't ride his coattails for their entire career. That's not how to succeed in science.
Great article. Thank you. Others have mentioned Hansen and his higher ECS estimates.
This recent paper has been published which finds that aerosol reductions, “decreased on average by 2.8 ± 1.2% per decade in the combined North Atlantic and Northeast Pacific regions between 2003 and 2022” (https://www.nature.com/articles/s41467-025-65127-x). It also finds that Earth System Models struggle to match this degree of change. The authors also wrote a nice Conversation article which gives a layman’s summary of their findings (https://theconversation.com/reduced-air-pollution-is-making-clouds-reflect-less-sunlight-269805). I found it helpful. Maybe others will too. I am pretty confused about all this.
My question: isn’t this exactly what Hansen predicted? Does this paper imply that, with a greater masking effect from aerosols, the finding of higher ECS must follow? Or is that an oversimplification?
When will feel confident enough about our aerosol estimates to know that ECS is high?
Hansen’s focus on recent warming acceleration and cloud/aerosol changes highlights real uncertainties, though — and importantly, Zeke doesn’t rule out the possibility that Hansen could be right.
But the broader takeaway really doesn’t change: we only stop warming once we reach net zero. The exact value of ECS mostly affects how quickly we need to get there, not the direction of travel.
Unfortunately, only the people who already accept that climate change is real, human-caused, and serious tend to care about these nuances — but they matter for understanding the trajectory we’re actually on.
I’d love to see a graph of ECS uncertainly projected into the future as observations brute force it to narrow. Would it be a linear narrowing from today to approximately 2100 under a current policies scenario?
More data does help screen out unrealistic models, but not because added warming tightens ECS directly. What really narrows things is improved observations of clouds, aerosols, radiative fluxes, and ocean heat uptake — those reveal which model feedbacks are realistic. So yes, more data helps with model evaluation, but the temperature record alone doesn’t shrink ECS uncertainty in a linear way.
Perhaps it is time to start predicting conditions at 2050 as well as those at 2100. Not only will it show the slowness (relative to a human lifetime) of change, but also can show the effects of different strategies to decarbonize.
We do get forecasts for a lot of things on an interim timeline: Adoption of renewable energy, deaths of corals, loss of this or that glacier, Amazon losing its "rainforest" status.
Considering climate uncertainty is so high I'm not sure how you could ever detect policy effects in warming (or even other system observables such as gas concentrations). Usually successful interventions require an ability to detect their effect in the outcome of interest. Borrowing from HR lingo in performance evaluation goal-setting, criteria should be SMART i.e. specific, measurable, achievable, relevant, and time-bound. If emission is free to bend down while concentration is free to bend up, it's tough to be SMART.
how do you reconcile the precision of the CF&D pathways or en-roads simulations you presented with your view also that Hansen is probably right that climate sensitivity is high. That is not SMART. In the evaluation of policy performance by the criteria of meeting or exceeding temperature targets it's a guaranteed fail.
My gut feeling is the quicker than expected cheaper renewables deployment was the heavier factor in lowering the worst case outlook. However, I see 2 C degrees by 2030 something because the carbon sinks to carbon sources scenario is not understood well ( you gotta be a prophet ) and also cloud albedo is nebulous (pun intended:) )
I just should have said outright that we've unleashed the self feeding heat beast and we should at least adapt with the wedoable surface reflection. Done enough it is a mitigation by reducing albedo whi h saves carbon sinks and saves cooli g energy expense.
If the models are so good.. why are we in the worst case ( heated ) zones of uncertainty all the time now? Models are educated guesses but c'mon we are heating more than the models predict.. oh.. except for margin for error. We are always in the bad zone of margin for error
I think Dr James Hansen beats the IPCC in thinking.
I get the appeal of trusting a single strong voice, but this is the same pattern we see with skeptics who elevate outliers like Christy, Curry, and the other authors of the recent DOE report over the broader scientific literature. Hansen is obviously a towering figure in climate science, but no single scientist — not even Hansen — represents “the science.”
The consensus is built from hundreds of groups evaluating independent lines of evidence: paleoclimate, energy balance, ocean heat content, satellite data, reanalysis, etc. That’s why Zeke’s chart matters: observed warming is currently tracking below the CMIP6 ensemble median, not above. Claims of an “accelerating” trend need to be evaluated against ENSO variability, aerosol reductions, and energy-imbalance data — not just eyeballing a short-term slope.
If we throw out the consensus whenever it’s inconvenient — whether to exaggerate risk or to downplay it — we end up with the same dynamic skeptics use.
Trust the body of evidence, not individual outliers.
I agree. Impartiality is fundamental to real science. The acceleration of global heating, which the models didn't catch ( the slope rise), is the concern. Hansen has an answer and you are right there are many other datasets needed but the models are begging for them. In short, no climate model right now can predict well with the unknown variabes like carbon sinks to source metamorphis, all aerosol effects ( bio and anthropic ), and cloud changes to name a few. And as far as incorporating varoabilities the question remains why do these variabilities exist and what causes the flux? It's just scary seeing and feeling the heat effects now.
Sometimes, it feels like a losing climate craps game
I share the sense of urgency — the heat impacts are real, and they’ve been getting worse. But I think it’s important to be precise about what is and is not happening in the data.
There isn’t clear evidence of an acceleration that’s outside model expectations.
If you isolate the long-term trend from ENSO, aerosol reductions, and short-term variability, the underlying warming rate is still broadly consistent with model projections. What we’re experiencing right now is a combination of (1) a very strong El Niño, (2) historically rapid aerosol declines from shipping, and (3) continuing high greenhouse forcing. That looks like acceleration, but it doesn’t mean the trend has broken out of the expected range.
On the model side:
You’re right — clouds, aerosols, and carbon-cycle feedbacks are tough. But that’s exactly why we don’t rely on a single model or a single scientist. The strength of climate science is in the ensemble and in the agreement across totally independent lines of evidence (oceans, satellites, paleoclimate, energy balance). All of them still point to roughly the same sensitivity: ~3°C per CO₂ doubling, give or take a bit.
So yes, the situation is serious. But it’s not “craps.” The physics isn’t random, and the uncertainties cut both ways, not only toward extreme outcomes.
The smartest thing we can do is base our expectations on the full body of evidence — not the scariest short-term spikes, and not the most optimistic outliers.
Am big on playing it safe by getting surface reflection out now in urban areas.. especially well insolated and populated. Hopefully, the temp spike was a glitch but am playing devil's advocate. It's hot in hell :)
The gap between the IEA CPS and STEPS is shocking considering that the STEPS was initially “sold” as a slightly forward-looking current policy scenario. It certainly validates, for me, the return of the CPS proper to their portfolio of scenarios.
Personally I might replace STEPS with an Expected Policies Scenario (EPS) based on a high forecasted likelihood of specific policies being implemented and sustained.
On the question about unrealistic scenarios or progress on technology or progress, it's worth noting that
1) the IEA "World Energy Outlook 2025" also suggests that, with both the STEPS and the CPS scenarios, global anthropogenic CO2 emissions are flattening; that
2) global anthropogenic CO2 emissions departed its previous, upwardly-escalating numbers about a dozen years ago; that
3) the just-published preprint of the "Global Carbon Budget 2025" assessment (Friedlingstein et.al.) projects that the overall cumulative anthropogenic CO2 emissions in 2025 will be pretty much the same as in 2024, continuing this trend; and that
4) other IEA reports over the past few years attributed continued success at globally "bending the CO2 emissions curve" to the development and commercialization of low-carbon technologies -- that are modular and mass-producible -- and are economically-competitive in the marketplace with fossil energy systems.
Examples cited by the IEA include solar photovoltaics, batteries, wind turbines, hybrid and battery-electric vehicles. And may include hydrogen fuel cells as they are mass-produced in greater numbers in the near future.
I agree that some IPCC scenarios were unrealistic (i.e., the supposed business-as-usual scenarios). However, we are also confirming that technological progress has already been substantial and I expect that it will remain critically important in getting control of the greenhouse characteristics of the Earth's atmosphere.
You said, "How much of this decline is driven by earlier scenarios being unrealistic vs progress on technology and policy is an interesting debate". Looking at Mauna Loa, it looks like your first suggestion is correct rather than the latter. Have a good day,
Hi Scott, there is not a particularly meaningful difference between scenarios in CO2 concentrations as-of-yet. Emissions are a more useful differentiator.
Thanks Zeke. We can at least be sure the current trend of CO2 concentration is lower than it would be in a counterfactual world without technology and policy. China's emissions, for example, appear to have peaked even though its energy demand is still soaring; under government policy, it's now being met with renewable and nuclear energy (https://www.nature.com/articles/d41586-024-02877-6). And see "IEA: Fossil-fuel use will peak before 2030 – unless ‘stated policies’ are abandoned" (https://www.carbonbrief.org/iea-fossil-fuel-use-will-peak-before-2030-unless-stated-policies-are-abandoned). No real breakthroughs and no guarantees, but incremental progress nonetheless.
What's your reason for trusting Hansen over the consensus of his trained, mutually disciplined specialist peers (not "parrots")? Do you think seniority alone is good enough? Science is done collectively, and he's just one peer among many. It's up to him to persuade the rest. How "right" has he been compared to others, in the judgement of other actual experts? Sorry, your untrained, undisciplined, unpublished "lay" opinion doesn't count, no matter how passionate you are.
As a rule climate outcomes tend to deliver results above, or well above, those predicted. Furthermore, today’s climate policy goals can no longer be relied on, in view of the mad stampede for Arctic oil and gas,combined with the oil industry’s successful defiance of all efforts to rein it in. Conservatively, the fossil fuels sector will kill 350m people by 2050 and over a billion by 2100, not including those who die of famine or water scarcity. Instead of attempting to predict degrees of heating, it is time the climate community got real and predicted human fatalities. Governments and corporates would find that less easy to ignore.
Precedent indicates that governments and corporations will have no problem ignoring projected (and actual) human fatalities.
Can you please provide references to support your figures ?
I started to say Julian's figures are in the ballpark, depending on the ballpark's dimensions. Then I realized I don't know where his numbers come from either. I'm familiar with some peer-reviewed estimates, e.g. https://www.nature.com/articles/s41467-023-41888-1:
"We find that US $143 billion per year of the costs of extreme events is attributable to climatic change. The majority (63%), of this is due to human loss of life."
And https://www.nature.com/articles/s41558-021-01058-x:
"Across all study countries, we find that 37.0% (range 20.5–76.3%) of warm-season heat-related deaths can be attributed to anthropogenic climate change and that increased mortality is evident on every continent. "
I don't see total attributable mortality adding up to 350 million within 25 years, nor over a billion by 2100.
OTOH, we're almost certain anthropogenic global warming has already killed at least one person (e.g. https://www.nature.com/articles/s41467-023-36289-3). To suggest it won't kill more before the trend of GMST is capped, is simply perverse. How many attributable deaths do lukewarmers need before they'll support collective decarbonization?
It is a mistake to assume climate deaths are the main impact of fossil fuels, Health data indicates that deaths from various forms of fossil fuel poisoning are at least ten times greater than (current) climate deaths. However, because this is down to chemistry, science largely feels free to ignore it. So start here, noting that "environment" is a greenwash term for industrial and domestic poisoning: https://www.who.int/data/gho/data/themes/public-health-and-environment
Hell, the wars over oil represent their own high death rate.
Another reason to stop using the stuff?
I have a very long list of problems with the oil&gas industry, even before we get to greenhouse gas emissions. They play up how indispensable they are while they're undermining alternatives.
Ah. Thanks for engaging. You're right that climate deaths aren't the only impact of fossil fuels on human health and biodiversity. There is abundant science on air and water quality degradation, and other social and ecological costs of the market-driven transfer of geologic carbon to the atmosphere by the gigatonnes annually. Individual scientists are free to ignore much of it, and specialize on another topic of interest to them: otherwise, they'd have no time for deep understanding of any topic, chemistry included.
That said, Svante Arrhenius was a chemist. Prof. Dessler has atmospheric chemistry on his CV. But he and Dr. Hausfather are climate specialists. That's why we talk mostly about climate change here. It doesn't mean "science" is ignoring the total human and biodiversity costs of this manifold tragedy of the commons. For example, this blog's authors also talk about the "free" market's ancient propensity to socialize all the transaction cost it can get away with, hence the economic term "social cost of carbon". It's the underlying reason anybody talks about anthropogenic climate change: who pays for the SCC, and who benefits by socializing it?
So why focus on climate-change attributable mortality? While any death is a tragedy for the victim if no one else, those that wouldn't have occurred in a counterfactual world where adding fossil CO2 to the atmosphere doesn't increase global heat content, tend to draw the public's attention: especially when the public is sweating through yet another record-breaking heat wave, and at least some deaths are attributable to the additional heat of the enhanced "greenhouse" effect; or when record-breaking flash floods, cyclonic storm surges and winds kill scores or thousands, some fraction of whom would *almost certainly* - so certainly that it would be perverse to withhold provisional agreement, even without one specific number or other - still be alive if not for anthropogenic climate change.
Collective decarbonization advocates should of course be aware of the economic drivers of all socialized cost, not just human mortality, and also of the ways for-profit disinformers propagate greenwash along with simple denialism, as reviewed in "Disinformation as an obstructionist strategy in climate change mitigation: a review of the scientific literature for a systemic understanding of the phenomenon" (https://open-research-europe.ec.europa.eu/articles/4-169/v2). These anti-collectivist strategies and tactics were developed by the tobacco industry, for one, before global warming was on most of the public's mind.
Today there's a documented billion-dollar industry selling bespoke bullshit to anyone with the motivation and resources to pay for it. All of science is consequently ignored, or worse, distorted and politicized by carbon capital foremost, as it has the most profit to lose from collective intervention in the otherwise-"free" market. The more "lay" people who consider the source and follow the actual money, the better, IMHO.
Put simply, death statistics register with the public more than do 1 or 2 degrees Celsius, or atmospheric ppm. It’s simply a communication tool for explaining to the average person the likely cost of fossil fuels.
Based on Dr. James Hansen's recent work, a TCS of 4.5˚C seems more likely than the IPCC's estimate of 3˚C from a doubling of atmospheric CO2 concentration (youtube.com/watch?v=D2abyXGvELI).
If Hansen is right, none of the study estimates here are realistic. His long history of being right should give the IPCC reason to reconsider.
The important question is no longer so much of projected warming - we are in big trouble. The real question is when will the US will get around to closing the growing US carbon price gap with the prices of our major trading partners? Rather than dragging its feet, the US must help close the growing global carbon price gap: the global average price is $5/tCO2e, but the IPCC-recommended estimates required for a chance at a livable future is a global price of $80/tCO2e this year, rising to $135/tCO2e in 2030 and to $690/tCO2e in 2100 (carboncashback.org/carbon-price-gap).
I disagree with Hansen that 4.5C ECS is particularly likely (though it is within the uncertainty range). The same folks he relies on for paleoclimate data find a value of ~3C per doubling CO2 more or less in line with the central estimate: https://www.science.org/doi/10.1126/sciadv.adk9461
But the climate response remains quite uncertain; we should plan for a risk of 4.5C ECS in our policy response!
TY so much for your article. It's so good to know, as terrifying as it is. I'm curious, what does a 4.5C policy response look like? Would it be possible to respond at all within the chaos from that amount of warming?
The response for 4.5C is buying a well equipped cave or become a stowaway on Elon's Mars ship.
Zeke,
How can you question Hansen when, before you were born, he was gathering the information and connecting the dots? And Jim is straightforward
Because I’m a scientist. Our job is to do our own studies, not just blindly trust those who came before. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019rg000678
About blindly, do you go on a 10 year study before an emergency operation? Blindly, is a sick word to use against Jim's work. He is helping save us.
Hansen may be old and wise, but he can still fool himself, which is why he submits his claims to non-sycophantic peer review. Hell, we could all use a little honest review by our "peers" before we make public claims! Zeke is helping to save us too, although maybe not the way you think he should. I'm guessing you're not their publishing peer, however.
I like Zeke toyourself. But, I take Hansen's word or knowledge over Zeke's.
Of course, don't blindly accept assertions. But, don't blindly refute when you know you are refuting someone with good will and much more experience than yourself.
A good scientist respects the work of a better scientist. You want links to carbon sinks becoming sources? The Eei feedback loop?
Science is a collective enterprise, because you are the easiest person to fool. It's more important for non-experts to trust the consensus of experts, rather than any one expert. All experts, however, must respect the unsparing mutual discipline of their peers. In this case, the range of supportable ECS estimates leaves room for both Hansen and Hausfather, either until models converge more closely than they do currently, or until CO2 has actually doubled and we see how hot the globe actually gets.
As Earth burns, I find more solace in the truth rather than severity. Jim Hansen's clarity mobilizes me to helping cool Earth.
Many a great scientist became a not-so-great scientist eventually.
Furthermore, old minds typically become less flexible and open to new ideas. Planck's idea that science advances one funeral at a time reflects that.
I don't think Hansen would appreciate you thinking of him as unquestionable. It's anathema to what being a scientist is all about.
Right on! Why are the climate parrots not listening to Jim H? He is always a step ahead and RIGHT.
How do you know? Are you Hansen's publishing peer?
No. The big point is there are many hundreds/thousands of scientists who would love to be a peer on one Jim's papers. Don't you climate parrots get it? Jim has been right and everybody wants to refute him. Call it climate envy.
People who aren't sufficiently exposed to the history, philosophy, culture, and practice of science, often have incorrect ideas about it. You're apparently one of them. No self-aware scientist is as sure of himself as you are. Knowledge, i.e. "justified true belief", is approached asymptotically and collectively, and proof is for mathematics and distilled beverages.
Besides, you lay zealots don't get it. Scientists who get their names on any published paper in a climate-science venue of record are "Jim's" ("Dr. Hansen's" to you) peers. They might love to be his co-author, but what they'd really love is to be first author on their own paper in *Science* or *Nature*. If Dr. Hansen's their co-author, so much the better, but they can't ride his coattails for their entire career. That's not how to succeed in science.
It appears Zeke has succeeded pretty well by now (e.g. https://www.science.org/doi/full/10.1126/sciadv.1601207), and is quoted by the journal's science news reporters (e.g. https://www.science.org/doi/full/10.1126/science.371.6527.334). IOW, he's a legitimate expert, even if Hansen is more famous. It still doesn't matter what you think, regardless.
Great article. Thank you. Others have mentioned Hansen and his higher ECS estimates.
This recent paper has been published which finds that aerosol reductions, “decreased on average by 2.8 ± 1.2% per decade in the combined North Atlantic and Northeast Pacific regions between 2003 and 2022” (https://www.nature.com/articles/s41467-025-65127-x). It also finds that Earth System Models struggle to match this degree of change. The authors also wrote a nice Conversation article which gives a layman’s summary of their findings (https://theconversation.com/reduced-air-pollution-is-making-clouds-reflect-less-sunlight-269805). I found it helpful. Maybe others will too. I am pretty confused about all this.
My question: isn’t this exactly what Hansen predicted? Does this paper imply that, with a greater masking effect from aerosols, the finding of higher ECS must follow? Or is that an oversimplification?
When will feel confident enough about our aerosol estimates to know that ECS is high?
Zeke and Andrew have discussed the range and consensus around ECS previously, https://www.theclimatebrink.com/p/revisiting-the-hot-model-problem?fbclid=IwAR07LNmoDvomP65vu95_ODqfF2YEspkfgvjNHaDYA6dlhA-m6NXgu6zJTzI . Their synthesis across paleoclimate evidence, observational energy-budget constraints, and careful model evaluation makes the ~3°C consensus very compelling. Because they take that broader, multi-line-of-evidence view, I tend to trust their interpretation more.
Hansen’s focus on recent warming acceleration and cloud/aerosol changes highlights real uncertainties, though — and importantly, Zeke doesn’t rule out the possibility that Hansen could be right.
But the broader takeaway really doesn’t change: we only stop warming once we reach net zero. The exact value of ECS mostly affects how quickly we need to get there, not the direction of travel.
Unfortunately, only the people who already accept that climate change is real, human-caused, and serious tend to care about these nuances — but they matter for understanding the trajectory we’re actually on.
I’d love to see a graph of ECS uncertainly projected into the future as observations brute force it to narrow. Would it be a linear narrowing from today to approximately 2100 under a current policies scenario?
More data does help screen out unrealistic models, but not because added warming tightens ECS directly. What really narrows things is improved observations of clouds, aerosols, radiative fluxes, and ocean heat uptake — those reveal which model feedbacks are realistic. So yes, more data helps with model evaluation, but the temperature record alone doesn’t shrink ECS uncertainty in a linear way.
Perusing section 4 of Sherwood et al has given me a better appreciation of this.
Perhaps it is time to start predicting conditions at 2050 as well as those at 2100. Not only will it show the slowness (relative to a human lifetime) of change, but also can show the effects of different strategies to decarbonize.
We do get forecasts for a lot of things on an interim timeline: Adoption of renewable energy, deaths of corals, loss of this or that glacier, Amazon losing its "rainforest" status.
Considering climate uncertainty is so high I'm not sure how you could ever detect policy effects in warming (or even other system observables such as gas concentrations). Usually successful interventions require an ability to detect their effect in the outcome of interest. Borrowing from HR lingo in performance evaluation goal-setting, criteria should be SMART i.e. specific, measurable, achievable, relevant, and time-bound. If emission is free to bend down while concentration is free to bend up, it's tough to be SMART.
Try En-ROADS for some insight into how to do that: bit.ly/cfd-is-half-the-15-solution.
Then learn more about Carbon Fee and Dividend: bit.ly/cfdresources.
And then help create political will to enable bipartisan legislation to do it: carboncashback.org/carbon-price-gap.
how do you reconcile the precision of the CF&D pathways or en-roads simulations you presented with your view also that Hansen is probably right that climate sensitivity is high. That is not SMART. In the evaluation of policy performance by the criteria of meeting or exceeding temperature targets it's a guaranteed fail.
My gut feeling is the quicker than expected cheaper renewables deployment was the heavier factor in lowering the worst case outlook. However, I see 2 C degrees by 2030 something because the carbon sinks to carbon sources scenario is not understood well ( you gotta be a prophet ) and also cloud albedo is nebulous (pun intended:) )
I just should have said outright that we've unleashed the self feeding heat beast and we should at least adapt with the wedoable surface reflection. Done enough it is a mitigation by reducing albedo whi h saves carbon sinks and saves cooli g energy expense.
[*increasing* albedo, I think you mean]
If the models are so good.. why are we in the worst case ( heated ) zones of uncertainty all the time now? Models are educated guesses but c'mon we are heating more than the models predict.. oh.. except for margin for error. We are always in the bad zone of margin for error
I think Dr James Hansen beats the IPCC in thinking.
Except warming is currently on the lower side of the range of model projections, at least for CMIP6: https://www.realclimate.org/index.php/climate-model-projections-compared-to-observations/
You got me there.. but look at the slope of the actual temperature. It's accelerating to go beyond the expected.
I get the appeal of trusting a single strong voice, but this is the same pattern we see with skeptics who elevate outliers like Christy, Curry, and the other authors of the recent DOE report over the broader scientific literature. Hansen is obviously a towering figure in climate science, but no single scientist — not even Hansen — represents “the science.”
The consensus is built from hundreds of groups evaluating independent lines of evidence: paleoclimate, energy balance, ocean heat content, satellite data, reanalysis, etc. That’s why Zeke’s chart matters: observed warming is currently tracking below the CMIP6 ensemble median, not above. Claims of an “accelerating” trend need to be evaluated against ENSO variability, aerosol reductions, and energy-imbalance data — not just eyeballing a short-term slope.
If we throw out the consensus whenever it’s inconvenient — whether to exaggerate risk or to downplay it — we end up with the same dynamic skeptics use.
Trust the body of evidence, not individual outliers.
I agree. Impartiality is fundamental to real science. The acceleration of global heating, which the models didn't catch ( the slope rise), is the concern. Hansen has an answer and you are right there are many other datasets needed but the models are begging for them. In short, no climate model right now can predict well with the unknown variabes like carbon sinks to source metamorphis, all aerosol effects ( bio and anthropic ), and cloud changes to name a few. And as far as incorporating varoabilities the question remains why do these variabilities exist and what causes the flux? It's just scary seeing and feeling the heat effects now.
Sometimes, it feels like a losing climate craps game
I share the sense of urgency — the heat impacts are real, and they’ve been getting worse. But I think it’s important to be precise about what is and is not happening in the data.
There isn’t clear evidence of an acceleration that’s outside model expectations.
If you isolate the long-term trend from ENSO, aerosol reductions, and short-term variability, the underlying warming rate is still broadly consistent with model projections. What we’re experiencing right now is a combination of (1) a very strong El Niño, (2) historically rapid aerosol declines from shipping, and (3) continuing high greenhouse forcing. That looks like acceleration, but it doesn’t mean the trend has broken out of the expected range.
On the model side:
You’re right — clouds, aerosols, and carbon-cycle feedbacks are tough. But that’s exactly why we don’t rely on a single model or a single scientist. The strength of climate science is in the ensemble and in the agreement across totally independent lines of evidence (oceans, satellites, paleoclimate, energy balance). All of them still point to roughly the same sensitivity: ~3°C per CO₂ doubling, give or take a bit.
So yes, the situation is serious. But it’s not “craps.” The physics isn’t random, and the uncertainties cut both ways, not only toward extreme outcomes.
The smartest thing we can do is base our expectations on the full body of evidence — not the scariest short-term spikes, and not the most optimistic outliers.
Well put.
Am big on playing it safe by getting surface reflection out now in urban areas.. especially well insolated and populated. Hopefully, the temp spike was a glitch but am playing devil's advocate. It's hot in hell :)
And they continue to accumulate pollution and profits. Pollution=Corruption=Alienation.
Can you please provide a/some references to support those figures ?
Each has a link in the text to the paper or the report in question. Its easy to find.
Apologies. I was responding to(or thought I was) to Julian Cribb's comment on your post which notes expected numbers of deaths.....
The gap between the IEA CPS and STEPS is shocking considering that the STEPS was initially “sold” as a slightly forward-looking current policy scenario. It certainly validates, for me, the return of the CPS proper to their portfolio of scenarios.
Personally I might replace STEPS with an Expected Policies Scenario (EPS) based on a high forecasted likelihood of specific policies being implemented and sustained.
I'm not entirely unhappy to see CPS return, as long as we are clear that it is a somewhat pessimistic view of policy follow-through.
On the question about unrealistic scenarios or progress on technology or progress, it's worth noting that
1) the IEA "World Energy Outlook 2025" also suggests that, with both the STEPS and the CPS scenarios, global anthropogenic CO2 emissions are flattening; that
2) global anthropogenic CO2 emissions departed its previous, upwardly-escalating numbers about a dozen years ago; that
3) the just-published preprint of the "Global Carbon Budget 2025" assessment (Friedlingstein et.al.) projects that the overall cumulative anthropogenic CO2 emissions in 2025 will be pretty much the same as in 2024, continuing this trend; and that
4) other IEA reports over the past few years attributed continued success at globally "bending the CO2 emissions curve" to the development and commercialization of low-carbon technologies -- that are modular and mass-producible -- and are economically-competitive in the marketplace with fossil energy systems.
Examples cited by the IEA include solar photovoltaics, batteries, wind turbines, hybrid and battery-electric vehicles. And may include hydrogen fuel cells as they are mass-produced in greater numbers in the near future.
I agree that some IPCC scenarios were unrealistic (i.e., the supposed business-as-usual scenarios). However, we are also confirming that technological progress has already been substantial and I expect that it will remain critically important in getting control of the greenhouse characteristics of the Earth's atmosphere.
Hi Zeke,
You said, "How much of this decline is driven by earlier scenarios being unrealistic vs progress on technology and policy is an interesting debate". Looking at Mauna Loa, it looks like your first suggestion is correct rather than the latter. Have a good day,
Hi Scott, there is not a particularly meaningful difference between scenarios in CO2 concentrations as-of-yet. Emissions are a more useful differentiator.
Thanks Zeke. We can at least be sure the current trend of CO2 concentration is lower than it would be in a counterfactual world without technology and policy. China's emissions, for example, appear to have peaked even though its energy demand is still soaring; under government policy, it's now being met with renewable and nuclear energy (https://www.nature.com/articles/d41586-024-02877-6). And see "IEA: Fossil-fuel use will peak before 2030 – unless ‘stated policies’ are abandoned" (https://www.carbonbrief.org/iea-fossil-fuel-use-will-peak-before-2030-unless-stated-policies-are-abandoned). No real breakthroughs and no guarantees, but incremental progress nonetheless.
What's your reason for trusting Hansen over the consensus of his trained, mutually disciplined specialist peers (not "parrots")? Do you think seniority alone is good enough? Science is done collectively, and he's just one peer among many. It's up to him to persuade the rest. How "right" has he been compared to others, in the judgement of other actual experts? Sorry, your untrained, undisciplined, unpublished "lay" opinion doesn't count, no matter how passionate you are.
tar baby.