Your work on the "point of no return" is indispensable and precisely because the stakes are that high, we want to respectfully suggest that the framework most climate scientists, including yourself, are working within may be missing half the picture.
Your Chapter 10 focuses, rightly, on the greenhouse gas blanket - the heat-trapping mechanism that must be stopped. But the planet's temperature is governed by two systems simultaneously: the blanket that traps heat, and the air conditioner that actively exports it. Mainstream climate science has focused overwhelmingly on the first.
COOLING THE CLIMATE WITH WATER
The second - the biosphere's capacity to cool the planet through evapotranspiration, water cycling, cloud formation and latent heat export - is systematically underweighted, including in IPCC models.
The numbers make this concrete. The cooling effect of evapotranspiration and cloud formation of the Amazon rainforest is two orders of magnitude greater than the cooling from carbon sequestration alone. The Amazon and other rainforests are enormous planetary heat pumps through the water cycle, probably offsetting an amount of forcing of the same magnitude as the increased GHG content of the atmosphere. Half of global heating may well be misattributed to the GHGs but actually may be caused by the degradation of the cooling water cycles driven by the biosphere.
LOWERING THE CLIMATE SENSITIVITY OF CO₂
A restored biosphere also shifts the Bowen ratio: more energy leaving the planet’s surface as latent heat, less as sensible heat. This means the same CO₂ concentration drives less surface warming if we increase evapotranspiration through increased vegetation, which also increases cloud cover and hence albedo.
THE COOLING POWER OF THE AMAZON RAINFOREST, THE LARGEST COOLING ORGAN OF THE PLANET
We estimate that Amazon collapse alone would drive an additional 2.0–2.5°C of warming globally, independent of CO₂ levels. This is not in your feedback equation. It is not in the IPCC's either.
You write that the danger of passing the point of no return is "taboo at IPCC." We would argue there is a second taboo: the possibility that decarbonization alone cannot get us back below that point, even if achieved rapidly. If the living systems that regulate planetary temperature continue collapsing while we phase out fossil fuels, we may phase out emissions and still cross this existential threshold, because we have dismantled the air conditioner at exactly the moment we needed it most.
THE GOOD NEWS
The good news is that this is the one lever that can be pulled fast, at scale, and at relatively low cost : restoring tropical forests and their water cycles. The science (Bunyard et al., 2024) and the implementation model (ARARA) already exist. What is missing is the integration: a Unified Cooling Strategy that treats decarbonization, biological sequestration, and water-cycle restoration as one indivisible project.
You said it yourself: "The climate system's delayed response provides time to take preventive actions, if the science is understood well enough to define effective policy actions." The science is there. The window is closing. The complete picture needs all the parts of the equation if we are to avert global climate catastrophe.
HI Rob, I just posted a piece on how our use of fire for tens of thousands of years have altered the forest complexity and the struggle for mesic species to re-evolve to the previous evolutionary climatic maximum where fire and water kept each other in balance. A lot can be said about the continued deforestation and the break up of cloud and as you rightly point out this is also climate forcing and should be taken much more seriously. The same could be said for nutrient based cloud formation over the oceans and how overfishing is a feedback loop through the nutrient loss of daily bioavailable recycling that plays out through the natural cycle. This is essential for the longevity and intensity of ocean forming clouds, with stratification as one of the most immediate negative feed back loops.
Thank you very much, very interesting article and we are of a similar mind. You describe an important aspect of the biosphere regeneration ''from the forest floor up''. Your fire-water axis framing is compelling, shifting from suppression to rehydration totally makes ecological sense. However passive protection isn't enough, we have done too much damage. We need to actively and strategically regenerate the biological and hydrological systems that keep fire in its place and give forests, especially rainforests a chance to regenerate. For this reason I am working on https://www.arara.earth/ as a platform to scale regeneration, especially in the tropical zone, where the processes (in both directions) can go very fast.
I just read an article on the rapid acceleration of global warming from 2014, and not once did it mention the huge damage done to our forests from the 2014-16 super El Nino and the effects this has had on cloud formation. I will check out the blog many thanks.
if one wants a picture into the future one need only look at the effects of massive deforestation in east Africa has had on rainfall regularity and temperature in that region. the long rains drying trend especially from 1980 is so strong that even climate models can nor reproduce it.
good comments refs from you both, agree with importance of huge damage done to our forests from the 2014-16 / 2023-24 El Nino including spiking CO2 emissions thereof; here a fellow traveller JCM says--I encourage everyone to join in as allies in environmental conservation and remediation, even if for no other reason than stabilizing climate indicator variables.
In conclusion, we show that even if annual mean precipitation may remain stable after deforestation, the tail of temperature, precipitation, and wind distribution broadens, making conditions more unfavorable.
A concise killer framing: ICON 5 km storm-resolving simulations show full Amazon deforestation produces ~3.8 °C warming, collapses latent heat flux by ~60 W/m², and doubles dry days. That’s comparable to major radiative forcings, yet land-use forcing remains marginal in attribution frameworks. This suggests biosphere thermodynamics is underweighted in climate risk assessments.
Of course none of that data or cumulative impacts on global climates dynamics will be found in any of the CMIP7 inputs or outputs. Therefore they’ll never make it into the IPCC AR7 either.
It will soon be forgotten and swept under the ghg forcing renew energy ideological carpet to collect dust. Climate scientists and activists are not looking holistically at interconnected systems. Hansen et al at Columbia being a fair exception to the rule.
"Extreme cold at the tropopause “wrings out” almost all water in upward moving air. Thus, little water makes it to the upper atmosphere above the 1 mb level, where it can be dissociated by extreme ultraviolet radiation. As a result, negligible water is escaping from Earth today."
Do you agree with this statement? If so, there's negligible water vapor available to carry latent heat away from the planet, as you claim. The temperature of the planet depends on the net energy transfer between the entire planet and outer space, not on the transfer of energy between the atmosphere and the earth's surface, as you seem to be saying.
Latent heat transport is one of the primary mechanisms through which that balance is maintained. When the water molecules go back from gas to liquid, the energy that is emitted is LWR, that does not need transport, these photones simply radiate out to a large extent (basically 50% unless there are obstructions such as dense water vapor (which happens with the afternoon thunderclouds over the tropical rainforests for instance) or CO2, but at the tropopause level these impacts are a lot smaller. Best see it as a two step airconditioning system with different mechanisms.
Rob, I do not see in your explanation how the latent heat exchange between the atmosphere and the earth's surface (trees, etc.) is transported or radiated or convected or by any other means is ejected from the entire planet to outer space. Why do you confine your explanation to mechanisms only within the atmosphere? What is the transport mechanism to outer space?
Wonderful inclusion of big words, but rubbish nonetheless. Notions of intra-planetary cooling cycles totally ignore the net planetary energy imbalance - more solar energy comes in vs energy released to Space. Try to understand Dr. Hansen's work better.
This one at least should be obvious to anyone who studied the problem: The climate sensitivity of CO₂ is not just dependent on the GHG: the Earth has become measurably more climate-sensitive since World War II, not only because of rising CO₂ concentrations, but because the removal of millions of square kilometers of tropical forest has fundamentally altered how the surface partitions energy. Tropical forests maintain a low Bowen ratio: they buffer temperature through massive evapotranspiration, feeding moisture back into the atmosphere and sustaining low cloud cover. Replace them with pasture or degraded land and that buffer disappears: sensible heat dominates, surfaces warm faster, and the atmosphere loses a key cooling mechanism. In other words, we have not just been adding forcing to the system, we have been making the system itself more responsive to forcing.
Yes, the planet is becoming darker, and clouds are very important, and not just clouds per se, but also their composition. Every imaginable human action makes things worse.
Not just darker, please try to understand the importance of the Bowen ratio. This is not just about albedo, it is about the ration between latent and sensible heat which affects the factual warming up of the atmosphere.
And statements like "The full importance of how the Earth naturally cooled itself millions of years ago should not escape us." The Earth cools itself by radiating heat which is an external relationship between Earth and Space, regardless of the heat _source_ - soil, rock, water, air. The Earth has been in and out of cooler regions of the galaxy. We are in an interglacial, the planet warms up, and it has moved into a "local warm pocket" in the galaxy. Moving latent heat higher into the atmosphere IS STILL held in by the blanket of CO2, SF6, NOx, etc. Putting CO2 into the atmosphere above where rainfall can bring it down (CO2 solubility in rain) via aircraft was a serious error. All while ignoring the oceans, which WERE the significant repairers of the climate in past ages, via the carbon/silicate cycles, all dependent on plankton, which we keep damaging.
The cooling of the planet had several phases, driven by biological evolution. The rise of flowering plants (angiosperms) fundamentally transformed Earth's climate by dramatically increasing transpiration, leaf litter decomposition, and mycorrhizal soil carbon sequestration, cooling the planet through enhanced evapotranspiration and drawdown of atmospheric CO₂. This started about 100 million years ago and allowed the continents to be further colonized by plants and forests.
Maybe try to understand my work a bit better before you use such harsh words? Not my first day on the job. What is your background? Here are our cooling calculations https://medcraveonline.com/IJBSBE/IJBSBE-09-00237.pdf, please take a look.
My own work, together with a group of people. Just because it has not been accepted, doesn't mean it isn't true. Operating from the Living Planet perspective, the regulation by the biosphere of the climate becomes a whole different story. Lovelock's Gaia hypothesis proposes that Earth's living organisms and their physical environment form a self-regulating system that actively maintains conditions suitable for life: temperature, atmospheric composition, ocean salinity , much like a living organism regulates its own biology.
Happy to send you the PDF, here is a quick AI summary (without most of the calculations): Cooling the Planet with Plants - Bunyard et al. (2024)
The Overlooked Cooling Engine
Climate debate fixates on CO₂, but the paper argues that the water cycle driven by vegetation - particularly tropical rainforests - is a vastly more powerful climate regulator than has been realized by mainstream climate science. Tropical rainforests cool the Earth not primarily by sequestering carbon, but by acting as heat pumps that move solar energy away from the surface and out to space.
Why the Tropics Are the Real Coolers
This is not coincidental. Tropical rainforests sit precisely in the belt that receives the greatest intensity of solar radiation year-round. Evolution placed the most powerful biological cooling machinery where the planet needs it most. The numbers reflect this: evapotranspiration over the Amazon absorbs roughly 41% of incoming solar energy at the surface, and when cloud formation is added, up to 80% of daily solar input is radiated back to space. The cooling from this latent heat transport by the tropical rainforests is calculated to be two magnitudes than the cooling from carbon sequestration alone.
The Angiosperm Revolution
About 100 million years ago, the rise of flowering plants (angiosperms) - with their broad, heavily veined leaves and deep root systems - was transformative. They transpire at least four times faster than earlier conifers, dramatically amplifying the hydrological cycle over land. This evolutionary leap is what gave tropical rainforests their extraordinary cooling power, and over geological time helped draw atmospheric CO₂ down from over 3,000 ppm to pre-industrial levels of 280 ppm.
The Biotic Pump
The forests don't just cool locally - they sustain themselves and their cooling function through the biotic pump. When water vapor condenses into clouds, it implodes in volume by over 1,200 times, pulling moist ocean air thousands of kilometers inland. This keeps the deep Amazon - far from any coast - as wet and productive as the forest's edge. Deforestation breaks this pump, with exponentially declining rainfall toward the interior, eventually producing desert conditions.
The Urgency
The paper calculates that restoring roughly 3 million km² of tropical closed-canopy forest could offset the entire current global energy imbalance measured by NASA. Reforesting cleared Amazon land alone covers more than a third of that target. The conclusion is stark: cutting emissions is necessary but insufficient - restoring tropical forest hydrology is the fastest lever we have to stabilize the climate, while the decarbonization continues at the fastest possible pace.
Thanks for another beautifully written explanation of a very complex subject. I hope you are right that public opinion will shift in favor of climate action in time to avoid the “point of no return.”
It sure doesn’t look promising right now, at least in the US. Fortunately, people in most other countries (including China) appear to understand the science better than we do.
The wild card that worries me is Russia, which may perceive that global warming would empower them by opening up huge areas for agriculture and development.
Just wondering if this is a valid concern, based on your interactions with Russian scientists?
The fact that numerous nations possess fossil fuels and can benefit from their use in different ways is a major reason that simple scenarios with rapid phaseout of emissions are unrealistic. That does not mean that the problem is unsolvable. One reason for the concept of a carbon fee, and border adjustments to make the fee global or near global, is too combat that problem. A country that continues to burn fossil fuels will soon be unable to sell products on the global market because the border adjustment will make their products uncompetitive. This process must be gradual because time is needed to develop truly competitive alternatives to many fossil fuel uses -- and we have done a poor job of planning. Still, it can be quite rapid, once we get started.
C'mon.. countries like Norway playing the big greenwash game while profiting off fossils that will go up in smoke on their same planet but not their backyard.
Fossils are way the f out of hand and no way will we get drawdown to work unless we get much more serious. It is now a fallacy the "fossils have their place" in this world.
To pass a durable, bipartisan carbon fee in the US and start healing the Earth we must "first do no harm" to either party's constituents..Blending "Fee and Dividend" with a "Carbon Fee and Payroll-tax Cut" might do the trick.
You are thinking too long term. Russia and Trump need to make money fast. That's why Greenland is key. Vandals can shut down the Panama canal for years by draining the lake with a million dollar missile... And the Suez canal can be shut with some speed boats and shoulder fired missiles... And the straight of Hormuz... Already shut. Then shipping has to go north where? North Sea! Russian/Chinese Ice breakers can collect a fee.. at least 11 billion per year. But Greenland's 200 mile EEZ sure would help collect those transit fees. Dont you think major oil distributers have been salivating over North Sea trade for the half century it has taken to Geo engineer such a marvel? ( The way they see it.)
Now the North route only allows 17m displacement but that's ok for Panamax and purchases of wide beam shallow draft ships are up 7% already. It won't take long for ship replacements to be made that allow the bulk of trade to avoid the cape of Good Hope.
Yes I know there are horrible side effects to this business plan. But the oil majors have been quite focused on it for a long time I think and it's hard for a big institutions to change direction.
Good news is, if we decide we don't want climate change, there are lots of industrial scale interventions we can make.
Forget about reforesting terrestrial land. The oceans used to be far more abundant thanks to the careful fertilization that the sperm whales and others would do. They have big brains, 200-year lifespans, global communications, excruciatingly detailed senses, and they eat plankton byproducts. They poop on the surface to grow that plankton. They're farmers. Before we killed 95% of the sperm whales, we know that the Southern oceans were not blue or green but orange with krill and bait fish. We can rebuild that system fairly quickly by acting like a whale, and monitoring the ocean and putting it in the right amount of fertilizer to make sure the nitrogen fixing Plankton and the carbon fixing Plankton are can get to work on a good fraction of the surface of the Earth. We can easily make an ice age with a tanker of iron. Let's not do that. Good thing we have thermostats.
And we have nuclear energy. The fusion from the Sun is wimpy. Fusion is a wimpy source of energy even if we could build it on Earth. A cubic meter of Sun is less powerful than a compost heap. If you want serious energy for industry, you should use the stored energy from a supernova. They blow stars away! And there's plenty of wound up potential energy left over from previous supernovas on Earth in the form of thorium and uranium. It's abundant in the ocean where plastic nets can absorb it out of the water. You can literally go fishing for fission fuel. Forever! As renewable as wind and waves...
Clean energy doesn't actually solve climate change by itself. But all those ridiculous business plans for carbon sequestration mechanically, start to make sense if you make industrial quality clean energy 10 times cheaper than coal. We easily can. But not if we ask utilitiy companies and corrupt politicians for permission.
If we upgrade to the best nuclear reactor technology from the Apollo era, the moon cell reactor, we can easily make energy 10 times cheap. And if we actually use automated manufacturing to construct nuclear reactors, that also makes it 10 times cheaper. And if we use some breeder reactors to eat up the waste and make new fuel, that also makes it 10 times cheaper, and eliminates the waste problem entirely. This is not new stuff.
No one on earth now knows how cheap and safe nuclear energy is in 2026. You don't know the quality or price of a manufactured product till the factory has 10 years to streamline the supply chain. There is no factory! Therefore no human being can no what the correct price and safety profile will be.
But I do know that if safe clean nuclear energy is 10 times cheaper than coal, people will stop buying carbon fuels. And I do know that at that price week in sequester lots of carbon.
In fact that molten salt reactor can kill two birds with one stone. It runs hot enough and is small enough to fit inside an existing coal-fired power plant. Then you can keep the plant operating with its turbines and generators if you want. But carbon emissions stop. China's already started on one of their fired power plants, and they have $151 more to do if they like the taste of that. Then China will have the lowest carbon emissions and the cheapest energy of anyone on the planet.
And they'll be able to use that cheap energy to pull carbon out of the ocean and atmosphere.
Some folks freak out about the fact that nuclear energy can be used for weapons. In context, 90% of the wars back to and including world war II were fought over oil. We haven't needed oil since the 1980s, if we had allowed it to be replaced by synthetic hydrocarbon fuels from cheap nuclear energy. , we could have slipped 90% of wars since 1989. Can you think of a major conflict that was not fought over oil? Or gas pipelines? Or almost entirely sponsored by oil revenues?
It's important as scientists not to be biased against solving problems with engineering. There has never been a point in human history where we could keep doing what we're doing without hitting some sustainability root block. It's innovate or die. That's the way it's always been.
Bands on geoengineering, are insane. We were allowed to emit carbon to melt the ice caps to allow North Sea shipping, and now we are not allowed to change our mind and fix that? Because we're worried about the side effects of cleaning up after ourselves?
We must not destroy Earth because we're worried about the unintended side effects of saving it.
Scientists must not fall for the panic mindset. Stop the world I want to get off is not an option. NetZero is merely a sad plea to God to save us because we've stopped making the problem worse. Even God knows not to give us credit for solving the second derivative of the actual problem. Let's clean up after ourselves, and maintain our spaceship so that it is comfortable and stable for sure with an engineering safety margin in case something unexpected happens. We don't know if it's hard if we haven't tried.
If we refuse to use new technology & settle for the junk the industry wants to sell off the shelf, we will fail.
Rick, my sentiments 100% too on Russia. They will get alot of global heating damage but they are already using the ice melt to their advantage. They'll pimp fossils to survive. And yes.. there might be for a period of time alot more suitable ag conditions.
Overall, Russia is the bad joker in the world's deck of nations with great abilities to fight climate change.
Over the years, I’ve had to supplement my income by “captaining” high end catering events in the homes of the richest people in the world. I have been in the room when national level Democrats bend the knee and swear to never tax billionaires, never regulate the finance industry, and never get in the way of private equity and hedge funds from continuing to make money off fossil fuels. These national level Dem pols start off by stating how grateful to Schumer and Jeffries for getting them access to these billionaires.
To paraphrase Malcom X, while the wolves may be Republicans, most Dems are foxes.
The change that must happen won’t come from these people. We have to vote in true progressives and Dem Socialists to get the Green New Deal passed, so that billionaires can’t play workers against environmentalists.
For starters, we need genuine campaign finance reform.
But wolves and foxes - and their innumerable supporters - are largely uninterested in undoing a system that has served them well enough to keep them in power sharing mode for many decades.
They should be beholden to public interest, not campaign donors.
To paraphrase one N.P.R. on air guest comment some years back, ‘I’ve known politicians who spend half their time trying to figure out what they can do for their ten biggest donors.’
The host’s reply? ‘I’ve known of some who spend ALL their time on that.’
So many “starters,” it feels overwhelming. Charles Koch has done a masterful job of amassing billionaires, creating infrastructure, buying media, politicians, and judges. I agree overturning Cotizens United is essential and campaign finance reform absolutely necessary to addressing wealth inequality which is the central threat to democracy. And climate change is the central threat to humanity. And they are totally intertwined.
Your framing of the "point of no return" as a consequence of delayed climate response resonated with work I've been doing to communicate exactly that problem visually.
As an engineer and former experimental physicist, my instinct when evaluating any system is to overlay independent diagnostics. Applied to climate, that means placing three completely independent datasets on the same CO₂–temperature axes: the deep-time equilibrium relationship from Cenozoic reconstructions spanning 66 million years (Judd et al., Science 2024), glacial–interglacial variability from Antarctic ice cores covering the past 800,000 years, and the modern instrumental record since 1850. These datasets were developed by different scientific communities, using different methods, to answer different questions. When plotted together, they converge.
What the composite makes structurally visible is what your chapter is describing: the physics has a destination, and that destination is not determined by models — it is written in the climate record itself. The Judd et al. equilibrium curve (AESS ≈ 8°C per CO₂ doubling) represents where the system is ultimately headed for a given CO₂ concentration, on the timescales that slow feedbacks require to fully express. The modern trajectory is currently running well below that curve — not because the physics has changed, but because the system hasn't finished responding yet. That is the disequilibrium your chapter is pointing at.
Kirsten Zickfeld and colleagues (Journal of Climate, 2013) put numbers on the commitment: after net-zero, 85–99% of peak warming persists 700 years after emissions cease, and atmospheric CO₂ remains above 50% of peak concentration at year 3000. The 2100 endpoint that dominates policy discussion is a waypoint, not a destination. The composite diagram makes that concrete — it shows where 66 million years of empirical data says the physics is pointing, independent of any model.
Runaway climate begins when people refuse to take the bus or train. That mindset will 🔥 us. Hyperbole and " Thou shalt's" and impressive numerical displays won't.
WE GOTTA REALLY TRULY CARE. The solution starts there.
I really hope Sophie's Planet becomes a best seller, a climate reference standard, and a movie. Why? Because.. Dr Hansen sees the most important numbers and correlates them in earnest. And he sees the urgency. There are many climate folk that go on wrongful and incomplete assessment of the climate fiasco. I would like to see his work get soaked up by internet osmosis. Hopefully, we can unite with a more honest,complete plan in accordance. And a movie is the new book. It could get the masses educated/inspired and the end result leave Sophie with a healthier planet that she thanks her grand dad for.
Looking forward to reading the whole thing together. I assume you'll link us to it when it's posted? Thanks greatly for all that you have done over the years to try to wake up humanity to the cliff they're headed towards (and may now, like Wile Coyote, have jumped off and haven't realized it yet).
Reading some of the debate here I would like to squeeze in another factor the inevitably escapes notice. There are over 8 billion humans on this planet. No amount of debate or persuasion will push them toward rational behavior. What we have now is not the prospect of runaway climate, but it's most important prelude, the runaway human stampede.
Dr Hansen - can you expand a bit more on the hyperthermal events caused by orbital eccentricity?
Your note says that the max eccentricity is around 7%, and am I right in assuming that the inverse square law would apply so the change in radiation would be sqrt(7)=2.6%?
So, a 2.6% change in radiation hitting the Earth can have dramatic effects on global climate? That seems so small... In our normal life a 2.6% variation would be seen as "small" and any system that couldn't tolerate that variance would be rightly described as "finely balanced". Perhaps there is a lesson there for us all.
The eccentricity change has insignificant effect on the annual global energy -- it only alters the seasonal and geographical distribution of the solar forcing. I have a later chapter on the orbital parameter effects. That's one of the chapters that I will send out for comments.
First step is phase change of water absorbing the energy in the transition from water to vapor, second is recondensation at cloud level where the energy is emitted in long wave radiation, 2 step airconditioning system.
Dear Professor Hansen,
Your work on the "point of no return" is indispensable and precisely because the stakes are that high, we want to respectfully suggest that the framework most climate scientists, including yourself, are working within may be missing half the picture.
Your Chapter 10 focuses, rightly, on the greenhouse gas blanket - the heat-trapping mechanism that must be stopped. But the planet's temperature is governed by two systems simultaneously: the blanket that traps heat, and the air conditioner that actively exports it. Mainstream climate science has focused overwhelmingly on the first.
COOLING THE CLIMATE WITH WATER
The second - the biosphere's capacity to cool the planet through evapotranspiration, water cycling, cloud formation and latent heat export - is systematically underweighted, including in IPCC models.
The numbers make this concrete. The cooling effect of evapotranspiration and cloud formation of the Amazon rainforest is two orders of magnitude greater than the cooling from carbon sequestration alone. The Amazon and other rainforests are enormous planetary heat pumps through the water cycle, probably offsetting an amount of forcing of the same magnitude as the increased GHG content of the atmosphere. Half of global heating may well be misattributed to the GHGs but actually may be caused by the degradation of the cooling water cycles driven by the biosphere.
LOWERING THE CLIMATE SENSITIVITY OF CO₂
A restored biosphere also shifts the Bowen ratio: more energy leaving the planet’s surface as latent heat, less as sensible heat. This means the same CO₂ concentration drives less surface warming if we increase evapotranspiration through increased vegetation, which also increases cloud cover and hence albedo.
THE COOLING POWER OF THE AMAZON RAINFOREST, THE LARGEST COOLING ORGAN OF THE PLANET
We estimate that Amazon collapse alone would drive an additional 2.0–2.5°C of warming globally, independent of CO₂ levels. This is not in your feedback equation. It is not in the IPCC's either.
You write that the danger of passing the point of no return is "taboo at IPCC." We would argue there is a second taboo: the possibility that decarbonization alone cannot get us back below that point, even if achieved rapidly. If the living systems that regulate planetary temperature continue collapsing while we phase out fossil fuels, we may phase out emissions and still cross this existential threshold, because we have dismantled the air conditioner at exactly the moment we needed it most.
THE GOOD NEWS
The good news is that this is the one lever that can be pulled fast, at scale, and at relatively low cost : restoring tropical forests and their water cycles. The science (Bunyard et al., 2024) and the implementation model (ARARA) already exist. What is missing is the integration: a Unified Cooling Strategy that treats decarbonization, biological sequestration, and water-cycle restoration as one indivisible project.
You said it yourself: "The climate system's delayed response provides time to take preventive actions, if the science is understood well enough to define effective policy actions." The science is there. The window is closing. The complete picture needs all the parts of the equation if we are to avert global climate catastrophe.
Hope to hear from you,
Kind regards,
Rob de Laet
HI Rob, I just posted a piece on how our use of fire for tens of thousands of years have altered the forest complexity and the struggle for mesic species to re-evolve to the previous evolutionary climatic maximum where fire and water kept each other in balance. A lot can be said about the continued deforestation and the break up of cloud and as you rightly point out this is also climate forcing and should be taken much more seriously. The same could be said for nutrient based cloud formation over the oceans and how overfishing is a feedback loop through the nutrient loss of daily bioavailable recycling that plays out through the natural cycle. This is essential for the longevity and intensity of ocean forming clouds, with stratification as one of the most immediate negative feed back loops.
https://substack.com/home/post/p-189242931
Thank you very much, very interesting article and we are of a similar mind. You describe an important aspect of the biosphere regeneration ''from the forest floor up''. Your fire-water axis framing is compelling, shifting from suppression to rehydration totally makes ecological sense. However passive protection isn't enough, we have done too much damage. We need to actively and strategically regenerate the biological and hydrological systems that keep fire in its place and give forests, especially rainforests a chance to regenerate. For this reason I am working on https://www.arara.earth/ as a platform to scale regeneration, especially in the tropical zone, where the processes (in both directions) can go very fast.
I just read an article on the rapid acceleration of global warming from 2014, and not once did it mention the huge damage done to our forests from the 2014-16 super El Nino and the effects this has had on cloud formation. I will check out the blog many thanks.
Indeed and still accelerating, look at the rainforest droughts/temp spikes of 2023/2024 as well.
if one wants a picture into the future one need only look at the effects of massive deforestation in east Africa has had on rainfall regularity and temperature in that region. the long rains drying trend especially from 1980 is so strong that even climate models can nor reproduce it.
good comments refs from you both, agree with importance of huge damage done to our forests from the 2014-16 / 2023-24 El Nino including spiking CO2 emissions thereof; here a fellow traveller JCM says--I encourage everyone to join in as allies in environmental conservation and remediation, even if for no other reason than stabilizing climate indicator variables.
https://www.realclimate.org/index.php/archives/2026/01/2025-updates/#comment-845210
In conclusion, we show that even if annual mean precipitation may remain stable after deforestation, the tail of temperature, precipitation, and wind distribution broadens, making conditions more unfavorable.
https://esd.copernicus.org/articles/17/167/2026/#section4
https://www.youtube.com/watch?v=yYsf1jK2Nrc
A concise killer framing: ICON 5 km storm-resolving simulations show full Amazon deforestation produces ~3.8 °C warming, collapses latent heat flux by ~60 W/m², and doubles dry days. That’s comparable to major radiative forcings, yet land-use forcing remains marginal in attribution frameworks. This suggests biosphere thermodynamics is underweighted in climate risk assessments.
Of course none of that data or cumulative impacts on global climates dynamics will be found in any of the CMIP7 inputs or outputs. Therefore they’ll never make it into the IPCC AR7 either.
It will soon be forgotten and swept under the ghg forcing renew energy ideological carpet to collect dust. Climate scientists and activists are not looking holistically at interconnected systems. Hansen et al at Columbia being a fair exception to the rule.
Tons of evidence, also for the Amazon, Central America and for instance Borneo.
Rob, Dr. Hanson writes in his article, above:
"Extreme cold at the tropopause “wrings out” almost all water in upward moving air. Thus, little water makes it to the upper atmosphere above the 1 mb level, where it can be dissociated by extreme ultraviolet radiation. As a result, negligible water is escaping from Earth today."
Do you agree with this statement? If so, there's negligible water vapor available to carry latent heat away from the planet, as you claim. The temperature of the planet depends on the net energy transfer between the entire planet and outer space, not on the transfer of energy between the atmosphere and the earth's surface, as you seem to be saying.
Latent heat transport is one of the primary mechanisms through which that balance is maintained. When the water molecules go back from gas to liquid, the energy that is emitted is LWR, that does not need transport, these photones simply radiate out to a large extent (basically 50% unless there are obstructions such as dense water vapor (which happens with the afternoon thunderclouds over the tropical rainforests for instance) or CO2, but at the tropopause level these impacts are a lot smaller. Best see it as a two step airconditioning system with different mechanisms.
Rob, I do not see in your explanation how the latent heat exchange between the atmosphere and the earth's surface (trees, etc.) is transported or radiated or convected or by any other means is ejected from the entire planet to outer space. Why do you confine your explanation to mechanisms only within the atmosphere? What is the transport mechanism to outer space?
Thank you Sam, let me chew on that.
Wonderful inclusion of big words, but rubbish nonetheless. Notions of intra-planetary cooling cycles totally ignore the net planetary energy imbalance - more solar energy comes in vs energy released to Space. Try to understand Dr. Hansen's work better.
This one at least should be obvious to anyone who studied the problem: The climate sensitivity of CO₂ is not just dependent on the GHG: the Earth has become measurably more climate-sensitive since World War II, not only because of rising CO₂ concentrations, but because the removal of millions of square kilometers of tropical forest has fundamentally altered how the surface partitions energy. Tropical forests maintain a low Bowen ratio: they buffer temperature through massive evapotranspiration, feeding moisture back into the atmosphere and sustaining low cloud cover. Replace them with pasture or degraded land and that buffer disappears: sensible heat dominates, surfaces warm faster, and the atmosphere loses a key cooling mechanism. In other words, we have not just been adding forcing to the system, we have been making the system itself more responsive to forcing.
Yes, the planet is becoming darker, and clouds are very important, and not just clouds per se, but also their composition. Every imaginable human action makes things worse.
Not just darker, please try to understand the importance of the Bowen ratio. This is not just about albedo, it is about the ration between latent and sensible heat which affects the factual warming up of the atmosphere.
And statements like "The full importance of how the Earth naturally cooled itself millions of years ago should not escape us." The Earth cools itself by radiating heat which is an external relationship between Earth and Space, regardless of the heat _source_ - soil, rock, water, air. The Earth has been in and out of cooler regions of the galaxy. We are in an interglacial, the planet warms up, and it has moved into a "local warm pocket" in the galaxy. Moving latent heat higher into the atmosphere IS STILL held in by the blanket of CO2, SF6, NOx, etc. Putting CO2 into the atmosphere above where rainfall can bring it down (CO2 solubility in rain) via aircraft was a serious error. All while ignoring the oceans, which WERE the significant repairers of the climate in past ages, via the carbon/silicate cycles, all dependent on plankton, which we keep damaging.
The cooling of the planet had several phases, driven by biological evolution. The rise of flowering plants (angiosperms) fundamentally transformed Earth's climate by dramatically increasing transpiration, leaf litter decomposition, and mycorrhizal soil carbon sequestration, cooling the planet through enhanced evapotranspiration and drawdown of atmospheric CO₂. This started about 100 million years ago and allowed the continents to be further colonized by plants and forests.
Maybe try to understand my work a bit better before you use such harsh words? Not my first day on the job. What is your background? Here are our cooling calculations https://medcraveonline.com/IJBSBE/IJBSBE-09-00237.pdf, please take a look.
Wut? Not a credible source.
My own work, together with a group of people. Just because it has not been accepted, doesn't mean it isn't true. Operating from the Living Planet perspective, the regulation by the biosphere of the climate becomes a whole different story. Lovelock's Gaia hypothesis proposes that Earth's living organisms and their physical environment form a self-regulating system that actively maintains conditions suitable for life: temperature, atmospheric composition, ocean salinity , much like a living organism regulates its own biology.
I think I agree. But there's no cooling in our future.
I can't open the file. Please give me the Cliff notes version.
Happy to send you the PDF, here is a quick AI summary (without most of the calculations): Cooling the Planet with Plants - Bunyard et al. (2024)
The Overlooked Cooling Engine
Climate debate fixates on CO₂, but the paper argues that the water cycle driven by vegetation - particularly tropical rainforests - is a vastly more powerful climate regulator than has been realized by mainstream climate science. Tropical rainforests cool the Earth not primarily by sequestering carbon, but by acting as heat pumps that move solar energy away from the surface and out to space.
Why the Tropics Are the Real Coolers
This is not coincidental. Tropical rainforests sit precisely in the belt that receives the greatest intensity of solar radiation year-round. Evolution placed the most powerful biological cooling machinery where the planet needs it most. The numbers reflect this: evapotranspiration over the Amazon absorbs roughly 41% of incoming solar energy at the surface, and when cloud formation is added, up to 80% of daily solar input is radiated back to space. The cooling from this latent heat transport by the tropical rainforests is calculated to be two magnitudes than the cooling from carbon sequestration alone.
The Angiosperm Revolution
About 100 million years ago, the rise of flowering plants (angiosperms) - with their broad, heavily veined leaves and deep root systems - was transformative. They transpire at least four times faster than earlier conifers, dramatically amplifying the hydrological cycle over land. This evolutionary leap is what gave tropical rainforests their extraordinary cooling power, and over geological time helped draw atmospheric CO₂ down from over 3,000 ppm to pre-industrial levels of 280 ppm.
The Biotic Pump
The forests don't just cool locally - they sustain themselves and their cooling function through the biotic pump. When water vapor condenses into clouds, it implodes in volume by over 1,200 times, pulling moist ocean air thousands of kilometers inland. This keeps the deep Amazon - far from any coast - as wet and productive as the forest's edge. Deforestation breaks this pump, with exponentially declining rainfall toward the interior, eventually producing desert conditions.
The Urgency
The paper calculates that restoring roughly 3 million km² of tropical closed-canopy forest could offset the entire current global energy imbalance measured by NASA. Reforesting cleared Amazon land alone covers more than a third of that target. The conclusion is stark: cutting emissions is necessary but insufficient - restoring tropical forest hydrology is the fastest lever we have to stabilize the climate, while the decarbonization continues at the fastest possible pace.
Thanks for another beautifully written explanation of a very complex subject. I hope you are right that public opinion will shift in favor of climate action in time to avoid the “point of no return.”
It sure doesn’t look promising right now, at least in the US. Fortunately, people in most other countries (including China) appear to understand the science better than we do.
The wild card that worries me is Russia, which may perceive that global warming would empower them by opening up huge areas for agriculture and development.
Just wondering if this is a valid concern, based on your interactions with Russian scientists?
The fact that numerous nations possess fossil fuels and can benefit from their use in different ways is a major reason that simple scenarios with rapid phaseout of emissions are unrealistic. That does not mean that the problem is unsolvable. One reason for the concept of a carbon fee, and border adjustments to make the fee global or near global, is too combat that problem. A country that continues to burn fossil fuels will soon be unable to sell products on the global market because the border adjustment will make their products uncompetitive. This process must be gradual because time is needed to develop truly competitive alternatives to many fossil fuel uses -- and we have done a poor job of planning. Still, it can be quite rapid, once we get started.
But Dr Hansen,
C'mon.. countries like Norway playing the big greenwash game while profiting off fossils that will go up in smoke on their same planet but not their backyard.
Fossils are way the f out of hand and no way will we get drawdown to work unless we get much more serious. It is now a fallacy the "fossils have their place" in this world.
Their place is back home in the ground.
To pass a durable, bipartisan carbon fee in the US and start healing the Earth we must "first do no harm" to either party's constituents..Blending "Fee and Dividend" with a "Carbon Fee and Payroll-tax Cut" might do the trick.
You are thinking too long term. Russia and Trump need to make money fast. That's why Greenland is key. Vandals can shut down the Panama canal for years by draining the lake with a million dollar missile... And the Suez canal can be shut with some speed boats and shoulder fired missiles... And the straight of Hormuz... Already shut. Then shipping has to go north where? North Sea! Russian/Chinese Ice breakers can collect a fee.. at least 11 billion per year. But Greenland's 200 mile EEZ sure would help collect those transit fees. Dont you think major oil distributers have been salivating over North Sea trade for the half century it has taken to Geo engineer such a marvel? ( The way they see it.)
Now the North route only allows 17m displacement but that's ok for Panamax and purchases of wide beam shallow draft ships are up 7% already. It won't take long for ship replacements to be made that allow the bulk of trade to avoid the cape of Good Hope.
Yes I know there are horrible side effects to this business plan. But the oil majors have been quite focused on it for a long time I think and it's hard for a big institutions to change direction.
Good news is, if we decide we don't want climate change, there are lots of industrial scale interventions we can make.
Forget about reforesting terrestrial land. The oceans used to be far more abundant thanks to the careful fertilization that the sperm whales and others would do. They have big brains, 200-year lifespans, global communications, excruciatingly detailed senses, and they eat plankton byproducts. They poop on the surface to grow that plankton. They're farmers. Before we killed 95% of the sperm whales, we know that the Southern oceans were not blue or green but orange with krill and bait fish. We can rebuild that system fairly quickly by acting like a whale, and monitoring the ocean and putting it in the right amount of fertilizer to make sure the nitrogen fixing Plankton and the carbon fixing Plankton are can get to work on a good fraction of the surface of the Earth. We can easily make an ice age with a tanker of iron. Let's not do that. Good thing we have thermostats.
And we have nuclear energy. The fusion from the Sun is wimpy. Fusion is a wimpy source of energy even if we could build it on Earth. A cubic meter of Sun is less powerful than a compost heap. If you want serious energy for industry, you should use the stored energy from a supernova. They blow stars away! And there's plenty of wound up potential energy left over from previous supernovas on Earth in the form of thorium and uranium. It's abundant in the ocean where plastic nets can absorb it out of the water. You can literally go fishing for fission fuel. Forever! As renewable as wind and waves...
Clean energy doesn't actually solve climate change by itself. But all those ridiculous business plans for carbon sequestration mechanically, start to make sense if you make industrial quality clean energy 10 times cheaper than coal. We easily can. But not if we ask utilitiy companies and corrupt politicians for permission.
If we upgrade to the best nuclear reactor technology from the Apollo era, the moon cell reactor, we can easily make energy 10 times cheap. And if we actually use automated manufacturing to construct nuclear reactors, that also makes it 10 times cheaper. And if we use some breeder reactors to eat up the waste and make new fuel, that also makes it 10 times cheaper, and eliminates the waste problem entirely. This is not new stuff.
No one on earth now knows how cheap and safe nuclear energy is in 2026. You don't know the quality or price of a manufactured product till the factory has 10 years to streamline the supply chain. There is no factory! Therefore no human being can no what the correct price and safety profile will be.
But I do know that if safe clean nuclear energy is 10 times cheaper than coal, people will stop buying carbon fuels. And I do know that at that price week in sequester lots of carbon.
In fact that molten salt reactor can kill two birds with one stone. It runs hot enough and is small enough to fit inside an existing coal-fired power plant. Then you can keep the plant operating with its turbines and generators if you want. But carbon emissions stop. China's already started on one of their fired power plants, and they have $151 more to do if they like the taste of that. Then China will have the lowest carbon emissions and the cheapest energy of anyone on the planet.
And they'll be able to use that cheap energy to pull carbon out of the ocean and atmosphere.
Some folks freak out about the fact that nuclear energy can be used for weapons. In context, 90% of the wars back to and including world war II were fought over oil. We haven't needed oil since the 1980s, if we had allowed it to be replaced by synthetic hydrocarbon fuels from cheap nuclear energy. , we could have slipped 90% of wars since 1989. Can you think of a major conflict that was not fought over oil? Or gas pipelines? Or almost entirely sponsored by oil revenues?
It's important as scientists not to be biased against solving problems with engineering. There has never been a point in human history where we could keep doing what we're doing without hitting some sustainability root block. It's innovate or die. That's the way it's always been.
Bands on geoengineering, are insane. We were allowed to emit carbon to melt the ice caps to allow North Sea shipping, and now we are not allowed to change our mind and fix that? Because we're worried about the side effects of cleaning up after ourselves?
We must not destroy Earth because we're worried about the unintended side effects of saving it.
Scientists must not fall for the panic mindset. Stop the world I want to get off is not an option. NetZero is merely a sad plea to God to save us because we've stopped making the problem worse. Even God knows not to give us credit for solving the second derivative of the actual problem. Let's clean up after ourselves, and maintain our spaceship so that it is comfortable and stable for sure with an engineering safety margin in case something unexpected happens. We don't know if it's hard if we haven't tried.
If we refuse to use new technology & settle for the junk the industry wants to sell off the shelf, we will fail.
All true. These days, nothing is too crazy.
Typos sorry. Moon Star reactor should be molten salt. $151 coal plants in China to be upgraded to nuclear should be 1151.
There is hope if we take the plunge:
https://substack.com/home/post/p-195352161
Rick, my sentiments 100% too on Russia. They will get alot of global heating damage but they are already using the ice melt to their advantage. They'll pimp fossils to survive. And yes.. there might be for a period of time alot more suitable ag conditions.
Overall, Russia is the bad joker in the world's deck of nations with great abilities to fight climate change.
I wouldn't trust Putin.
I wouldn't trust a fossil CEO.
I wouldn't trust Trump.
I trust my Mom, RIP. She taught me we gotta care.
H2Ouston.. we have a problem!
Lamedown and Crawldown won't save us.
Ignorance of the numbers and their true meanings is not getting through to ones who could and would do more.
Whether we become Vearthnus ( thank God for the oceans ) or Eeaaorth.
Thank you Dr H.! 😊 We all need concerned scientists like you.
Watt me 2 I ask myself as Earth 🔥?
Whoops.. meant "Knowledge" en lieu of "Ignorance" (sic).
there's edit / delete functions under the ' ... ' [3 dots] to the right of your comments.
Over the years, I’ve had to supplement my income by “captaining” high end catering events in the homes of the richest people in the world. I have been in the room when national level Democrats bend the knee and swear to never tax billionaires, never regulate the finance industry, and never get in the way of private equity and hedge funds from continuing to make money off fossil fuels. These national level Dem pols start off by stating how grateful to Schumer and Jeffries for getting them access to these billionaires.
To paraphrase Malcom X, while the wolves may be Republicans, most Dems are foxes.
The change that must happen won’t come from these people. We have to vote in true progressives and Dem Socialists to get the Green New Deal passed, so that billionaires can’t play workers against environmentalists.
For starters, we need genuine campaign finance reform.
But wolves and foxes - and their innumerable supporters - are largely uninterested in undoing a system that has served them well enough to keep them in power sharing mode for many decades.
They should be beholden to public interest, not campaign donors.
To paraphrase one N.P.R. on air guest comment some years back, ‘I’ve known politicians who spend half their time trying to figure out what they can do for their ten biggest donors.’
The host’s reply? ‘I’ve known of some who spend ALL their time on that.’
So many “starters,” it feels overwhelming. Charles Koch has done a masterful job of amassing billionaires, creating infrastructure, buying media, politicians, and judges. I agree overturning Cotizens United is essential and campaign finance reform absolutely necessary to addressing wealth inequality which is the central threat to democracy. And climate change is the central threat to humanity. And they are totally intertwined.
Your framing of the "point of no return" as a consequence of delayed climate response resonated with work I've been doing to communicate exactly that problem visually.
As an engineer and former experimental physicist, my instinct when evaluating any system is to overlay independent diagnostics. Applied to climate, that means placing three completely independent datasets on the same CO₂–temperature axes: the deep-time equilibrium relationship from Cenozoic reconstructions spanning 66 million years (Judd et al., Science 2024), glacial–interglacial variability from Antarctic ice cores covering the past 800,000 years, and the modern instrumental record since 1850. These datasets were developed by different scientific communities, using different methods, to answer different questions. When plotted together, they converge.
What the composite makes structurally visible is what your chapter is describing: the physics has a destination, and that destination is not determined by models — it is written in the climate record itself. The Judd et al. equilibrium curve (AESS ≈ 8°C per CO₂ doubling) represents where the system is ultimately headed for a given CO₂ concentration, on the timescales that slow feedbacks require to fully express. The modern trajectory is currently running well below that curve — not because the physics has changed, but because the system hasn't finished responding yet. That is the disequilibrium your chapter is pointing at.
Kirsten Zickfeld and colleagues (Journal of Climate, 2013) put numbers on the commitment: after net-zero, 85–99% of peak warming persists 700 years after emissions cease, and atmospheric CO₂ remains above 50% of peak concentration at year 3000. The 2100 endpoint that dominates policy discussion is a waypoint, not a destination. The composite diagram makes that concrete — it shows where 66 million years of empirical data says the physics is pointing, independent of any model.
For anyone interested, the most recent post developing these arguments is here: https://justdean.substack.com/p/how-one-diagram-reveals-the-climate
The fallacy of direct dividends is it goes contrary to the intent of carbon taxation. "Burn more, Baby, burn more with your dividend".
We gotta stop carbon not subsidize it with dividends.
Do the carbon tax the right way. In the spirit of decreasing fossil burning.
1. Tax the hell out of carbon in the points of inception.
2. Immediately send a stimulus check for rising fossil taxed causes.
3. Use the carbon tax to decarbonize, eg, mass trans, urban cooling, energy efficiency subsidies,ev subsidies, etc.
We gotta play the game knowing the rules and what winning is.
Just dividends looks like confetti burning up above the flames.
Dr Hansen,
Runaway climate begins when people refuse to take the bus or train. That mindset will 🔥 us. Hyperbole and " Thou shalt's" and impressive numerical displays won't.
WE GOTTA REALLY TRULY CARE. The solution starts there.
I really hope Sophie's Planet becomes a best seller, a climate reference standard, and a movie. Why? Because.. Dr Hansen sees the most important numbers and correlates them in earnest. And he sees the urgency. There are many climate folk that go on wrongful and incomplete assessment of the climate fiasco. I would like to see his work get soaked up by internet osmosis. Hopefully, we can unite with a more honest,complete plan in accordance. And a movie is the new book. It could get the masses educated/inspired and the end result leave Sophie with a healthier planet that she thanks her grand dad for.
And we all thank him for.
Looking forward to reading the whole thing together. I assume you'll link us to it when it's posted? Thanks greatly for all that you have done over the years to try to wake up humanity to the cliff they're headed towards (and may now, like Wile Coyote, have jumped off and haven't realized it yet).
Reading some of the debate here I would like to squeeze in another factor the inevitably escapes notice. There are over 8 billion humans on this planet. No amount of debate or persuasion will push them toward rational behavior. What we have now is not the prospect of runaway climate, but it's most important prelude, the runaway human stampede.
There is hope if we take the plunge:
https://substack.com/home/post/p-195352161
Dr Hansen - can you expand a bit more on the hyperthermal events caused by orbital eccentricity?
Your note says that the max eccentricity is around 7%, and am I right in assuming that the inverse square law would apply so the change in radiation would be sqrt(7)=2.6%?
So, a 2.6% change in radiation hitting the Earth can have dramatic effects on global climate? That seems so small... In our normal life a 2.6% variation would be seen as "small" and any system that couldn't tolerate that variance would be rightly described as "finely balanced". Perhaps there is a lesson there for us all.
The eccentricity change has insignificant effect on the annual global energy -- it only alters the seasonal and geographical distribution of the solar forcing. I have a later chapter on the orbital parameter effects. That's one of the chapters that I will send out for comments.
Dr Hansen,
You had brought up the Faustian bargain as a great analogy. The devil is in the details.. his greatest trick is convincing us we aren't 🔥.
GeoengineeringWatch.org’s groundbreaking documentary that conclusively exposes the existence of global weather intervention operations
https://geoengineeringwatch.org/the-dimming-full-length-climate-engineering-documentary/
Made a video based on a summary of this post https://earthclimate.eu/2026/06/22/hansen-on-runaway-climate-the-point-of-no-return/
First step is phase change of water absorbing the energy in the transition from water to vapor, second is recondensation at cloud level where the energy is emitted in long wave radiation, 2 step airconditioning system.