Equilibrium for CO2e doubling

[John Nissen]

Hi Mike, 

Without GHGs the planet would be 33C cooler at equilibrium.  Water vapour provides about half the GHG effect [1]; let's say 17C, leaving 16C from CO2, methane, etc.  The doubling of CO2e should add another 16C to the planet's equilibrium temperature, assuming water vapour hasn't changed (which it has, upward) and assuming albedo hasn't changed (which it has, downward).  Does this mean that the equilibrium temperature for CO2e doubling (which we've very nearly reached) must be in the region of 16C above the pre-industrial times when the ES was in equilibrium.   This is far from the 1.5C that we have reached.

The implication is that temperature rise is proportional to the GHG level to a first approximation.  If net zero is reached in 2050, by which time CO2e will certainly have doubled, the planet will continue to warm towards the equilibrium temperature which will be far higher.  The idea that the temperature will "stabilise" at net zero is fundamentally flawed.  To lower the global temperature, cooling intervention is required with a cooling power greater than the heating power from excess GHGs - and from increased H2O and lost albedo to boot.  This could amount to over 4 W/m2 or 2 petawatt couldn't it?

Cheers, John

[1] https://science.nasa.gov/earth/climate-change/steamy-relationships-how-atmospheric-water-vapor-amplifies-earths-greenhouse-effect/

Water vapor is Earth’s most abundant greenhouse gas. It’s responsible for about half of Earth’s greenhouse effect — the process that occurs when gases in Earth’s atmosphere trap the Sun’s heat. Greenhouse gases keep our planet livable. Without them, Earth’s surface temperature would be about 59 degrees Fahrenheit (33 degrees Celsius) colder.

[Michael MacCracken]

John--Not at all. It is not at all linear.

Mike

[John Nissen]

Hi Mike,

It should be linear to a first approximation.  A doubling of GHG forcing should move the equilibrium temperature about twice as far from where it would have been without any GHG forcing.  There must be another explanation if 16C equilibrium temperature is way out.  I'd hoped you'd come out with it. 

BTW, who's equilibrium temperature do you support, since there are many around?  David Wasdell has the highest I've seen, but nowhere near 16C.  Some seem to be as low as 3C - my foot.

Cheers, John

[Michael MacCracken]

Hi John--I don't really understand your thinking on this. CO2 forcing is logarithmic in concentration. IR radiation is proportional to the fourth power of temperature. If you are saying things are sort of linear with small change, okay, but you were going back to the Earth with no GHGs and that is not linear. In addition, the calculation of 33 C is based on a planetary average, daily average calculation rather that considering the day-night cycle, latitudinal effects or not. Without any GHGs, the Earth would be like the Moon--get heated in sunlight and go to very cold temperatures at night. the oceans would largely be frozen and there would be no clouds so the albedo would be very different--lower if no water and clouds at all, higher if there were water and frozen. And you seem to be mixing up climate sensitivity with equilibrium temperature.

I just don't think this discussion is on a useful track at all.

Mike

On 3/1/26 12:38 PM, John Nissen wrote:

Hi Mike,

It should be linear to a first approximation.  A doubling of GHG forcing should move the equilibrium temperature about twice as far from where it would have been without any GHG forcing.  There must be another explanation if 16C equilibrium temperature is way out.  I'd hoped you'd come out with it. 

BTW, who's equilibrium temperature do you support, since there are many around?  David Wasdell has the highest I've seen, but nowhere near 16C.  Some seem to be as low as 3C - my foot.

Cheers, John

On Sun, Mar 1, 2026 at 1:47 AM Michael MacCracken <mmac...@comcast.net> wrote:

John--Not at all. It is not at all linear.

Mike

On 2/28/26 5:04 PM, John Nissen wrote:

Hi Mike, 

Without GHGs the planet would be 33C cooler at equilibrium.  Water vapour provides about half the GHG effect [1]; let's say 17C, leaving 16C from CO2, methane, etc.  The doubling of CO2e should add another 16C to the planet's equilibrium temperature, assuming water vapour hasn't changed (which it has, upward) and assuming albedo hasn't changed (which it has, downward).  Does this mean that the equilibrium temperature for CO2e doubling (which we've very nearly reached) must be in the region of 16C above the pre-industrial times when the ES was in equilibrium.   This is far from the 1.5C that we have reached.

The implication is that temperature rise is proportional to the GHG level to a first approximation.  If net zero is reached in 2050, by which time CO2e will certainly have doubled, the planet will continue to warm towards the equilibrium temperature which will be far higher.  The idea that the temperature will "stabilise" at net zero is fundamentally flawed.  To lower the global temperature, cooling intervention is required with a cooling power greater than the heating power from excess GHGs - and from increased H2O and lost albedo to boot.  This could amount to over 4 W/m2 or 2 petawatt couldn't it?

Cheers, John

[1] https://science.nasa.gov/earth/climate-change/steamy-relationships-how-atmospheric-water-vapor-amplifies-earths-greenhouse-effect/

Water vapor is Earth’s most abundant greenhouse gas. It’s responsible for about half of Earth’s greenhouse effect — the process that occurs when gases in Earth’s atmosphere trap the Sun’s heat. Greenhouse gases keep our planet livable. Without them, Earth’s surface temperature would be about 59 degrees Fahrenheit (33 degrees Celsius) colder.

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[John Nissen]

Hi Mike,

I was trying to do a reality check on the claim that the achievement of net zero would "stabilise" the temperature.  I've been worried that the equilibrium temperature for a doubling of CO2e might be much more than some are claiming, e.g. 3C.  It occurred to me that one could look at the effect of GHGs on the Earth's temperature, and then consider doubling the CO2e part.  The effect of GHGs, including water vapour, on the Earth's temperature is commonly given as 33C.  

What I didn't do was consider the level of GHGs assumed for that 33C.  It might not have been the preindustrial level, for which CO2e is 280 ppm.  It might have been for the current level.  But this would not make much difference: only 1.5C perhaps.  

I assumed water vapour was about half, according to the NASA reference I gave.  From AR6 [1] the water vapour forcing comes to about 2.8 W/m2 at 1.5C, which is similar to the current forcing from CO2 and other gases combined.  Hence that half is about right.

So if my 16C equilibrium temperature is wildly out, the estimate of 33C must also be wildly out.  You point out that, without GHGs, there'd be a lot of snow and ice around which would lower the temperature.  Do you think they took that into account in the estimate of 33C?

Cheers, John

[1] AR6 WG1 Chapter 7

https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-7/

7.4.2.2 Water-vapour and Temperature Lapse-rate Feedbacks

The specific humidity (WV) feedback, also known as the water-vapour feedback, quantifies the change in radiative flux at the TOA due to changes in atmospheric water vapour concentration associated with a change in global mean surface air temperature. According to theory, observations and models, the water vapour increase approximately follows the Clausius–Clapeyron relationship at the global scale with regional differences dominated by dynamical processes (Section 8.2.1; Sherwood et al., 2010a; Chung et al., 2014; Romps, 2014; R. Liu et al., 2018; Schröder et al., 2019). Greater atmospheric water vapour content, particularly in the upper troposphere, results in enhanced absorption of LW and SW radiation and reduced outgoing radiation. This is a positive feedback. Atmospheric moistening has been detected in satellite records (Section 2.3.1.3.3), it is simulated by climate models (Section 3.3.2.2), and the estimates agree within model and observational uncertainty (Soden et al., 2005; Dessler, 2013; Gordon et al., 2013; Chung et al., 2014). The estimate of this feedback inferred from satellite observations is

α WV= 1.85 ± 0.32 W m^–2°C^–1(R. Liu et al., 2018). 

This is consistent with the value α WV= 1.77 ± 0.20 W m^–2°C^–1(one standard deviation) obtained with CMIP5 and CMIP6 models (Zelinka et al., 2020).

[Michael MacCracken]

Hi John--The temperature of 255 K for the world with no atmosphere is just solving the Stefan-Boltzmann equation for the temperature assuming a 30% albedo for the amount of energy going in and out. The mid-20th century average of observed temperature around the world was about 15 C (or about 288K), and the difference is 33 C. So nothing detailed at all. The surface temperature depends on both water vapor and CO2 GH effects. I don't think you can divide them as you are thinking and I don't think that they are linear, and each develops feedbacks and those will depend on the temperature at any given point. It is just not possible to linearize based on the 33 C difference.

If you want to get a natural estimate of climate sensitivity, seek to get it from Earth's climatic history. Soviet scientists did this and got 3 C for the sensitivity given the climatic state we are in now. Hoffert and Covey in a paper in Nature 30 some years ago did an analysis and got about the same central value that gives about the same range as IPCC is using. In my view, if the sensitivity is well higher than this, it is hard to see how the temperature through the Holocene could have been as nearly stable as it was. And then also, if it is significantly smaller that 3 C, it is hard to understand how we could have had such a large range between glacial and interglacial conditions.

It is also not clear that the sensitivity is the same for all types of forcings. As I mentioned, using the IPCC approach to evaluation, orbital parameter changes have virtually no global and annual average effect, but drove the quite large glacial-interglacial changes in climate just by redistributing solar energy by season and latitude. Exerting a change in radiative forcing in the atmosphere versus at the surface (i.e., above or below the water vapor GH effect) can have an effect (see past modeling studies by Govindasamy. Bala). Changing baseline amounts of sea ice, etc., can have an effect on the sensitivity, and the timescales of some feedbacks can change how fast one sees a response (e.g., consider times for subsidence and rebound to occur).

So, the simple attempt at reckoning you are attempting is fraught with problems. What Jim Hansen is doing is looking at various processes and feedbacks, so much more intimately at how the models are working, and looking at consistencies and inconsistencies with observations and responses and suggesting the most general sensitivity may be toward the upper limit of the typical uncertainty spread. Interesting to be doing, but making sure you are quantitatively consistent across all possible hidden feedbacks and relationships is really hard to be sure of--and is why the range suggested in the IPCC assessments has not narrowed much at all. We've got enough of a likelihood of global catastrophe in terms of impacts if the climate sensitivity is only 2 or 2.5 C given the consequences that can be seen in Earth history of a warming (e.g., during Eemian interglacial about 120-125 ka, global average temperature was maybe 1 C over preindustrial and sea level was 10 to 20 meters higher than at present). My recommendation is to just stick to the agreed sensitivity, and if the resulting impacts aren't viewed as serious enough to cause alarm and action, then we are likely doomed, so we need to keep working to educate people about impacts--we are at 1.5 and Arctic region is being seriously disrupted and we are not yet at equilibrium, especially for the cryosphere. Turning the climate ship from its present course will take time and waiting until it gets fully turned is too late to change things--as the UNFCCC states, the appropriate decision framework to use is the Precautionary Principle--doing so certainly instead of using the scientific tradition of mainly focusing on changes in the likely central value given that it is likely that it is the fairly unlikely extremes that will be wreaking havoc.

Best, Mike

[John Nissen]

Hi Mike,

I am very suspicious  of getting climate sensitivity from the Earth's history, since major changes in climate during the Quaternary were driven by Milankovitch cycles, collapse of ice sheets (or ice dams, e.g. for lake Agassiz), and large volcanic eruptions (e.g. Toba around 70kya).  I don't know of any definite CO2 driven climate change, except slow changes prior to the Quaternary which are debatable [1].  The correlation between temperature and CO2 can be explained by the fact that cooling water draws down CO2 (e.g. after Pinatubo) and warming water expels CO2.

So in explaining the 33C, we might look at planetary albedo, which you say was assumed to be 30% "for the amount of energy going in and out".  However 30% is the estimate for the albedo today.

SO2 may be clouding the issue.  Often overlooked, SO2 cooling exceeded GHG warming from about 1940 to 1970, causing both global cooling and Arctic cooling.  Hansen thinks that IPCC grossly underestimated the effect of SO2: the Earth's albedo since 2000 is well correlated with levels of SO2 in the atmosphere, and anomaly maps suggest that a deliberate reduction in ship SO2 "pollution" has had a significant effect.  Hansen calls this a Faustian bargain.  

When Hansen says 62% of albedo change is due to cloud effects (quoted by Robert Tulip in his MEER talk), I think he is referring to SO2. Removal of SO2 will make the equilibrium temperature for CO2 doubling even higher!

So you haven't convinced me that the equilibrium temperature for CO2e doubling isn't far higher than IPCC suggests.  Achieving net zero will not have the predicted effect of stabilising the global temperature.  This makes global cooling intervention urgent; but the refreezing of the Arctic is even more urgent because of tipping processes becoming unstoppable.

BTW, Ron's efforts to draw attention to ship SO2, and to call for a reversal of the reduction policy, are commendable.  Such a call might be welcome in some quarters: worth a try.

Cheers, John

[1] Badger eit al. (AGU, 2013)

CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/palo.20015

Abstract

The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 million years (Myr) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the “greenhouse” of the early Eocene to the “icehouse” of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive δ¹³C excursion known as carbon maximum 6 (“CM6”), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO₂ drawdown. More recently, it has been suggested that the δ¹³C excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO₂. Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (~300 ppm) atmospheric pCO₂ at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO₂ decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling.

[Michael MacCracken]

Hi John--Most of the items that make you suspicious are  short-term--looking over longer scales, atmospheric composition and continental drift (e.g., mountain building, altering of ocean currents) are major factors. 

On the albedo issue and 33 C, indeed choosing 30% is arbitrary--but that is what was done, along with it being a zero dimensional calculation.

On your comment about 1940 to 1970 cooling, in my view, the peak in warming during WWII is an artifact--a bias created by various issues regarding ocean conditions (change in measurement methods, mix of ships, and more) that does not really show up over land. Put your finger over the WWII time period and you get a different perspective on what was going on. Also, of course, the cleaning up of air pollution by lofting pollution through tall stacks instead of emissions at ground level that blackened cities di increase the likely sulfate loading a lot, as surface emitted SO2 has a lifetime of a day or two so little contribution to tropospheric haze whereas lofted emissions likely have a lifetime of a week or two and so are the real creators of the tropospheric haze. I do agree that reduced marine SO2 emissions have likely reduced the planetary albedo, which is why I've supported the idea of widely dispersed injection of SO2 into the mid- to upper troposphere, especially over low albedo remote ocean areas as a possible cooling intervention. In my view, doing this would be more spread out and efficient than just stepping down the marine emission standard out over the ocean.

And I agree with you on benefits of refreezing the Arctic and am working on some thoughts about this (first have to convince myself about it).

Best, Mike

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[John Nissen]

Hi Mike,

I still don't understand what could be wrong with my argument.  But the 16C equilibrium for CO2e doubling must be far too high, considering the end Permian extinction when CO2 levels increased 4 to 6-fold but the global temperature only increased 5-10C [1].  Though, could the warming back then have been masked by huge amounts of SO2 from the Siberian Traps volcanic eruptions?

I do hope you convince yourself about the benefits of refreezing the Arctic, especially to reverse the several tipping processes that currently threaten catastrophic climate change and/or sea level rise.

Cheers, John

[1] AI overview

At the end of the Permian period (approximately 252 million years ago), the Earth experienced extreme global warming and a massive, rapid spike in atmospheric

concentration, primarily driven by the Siberian Traps volcanic eruptions. 

Atmospheric

Concentration

• Rapid Rise:
  
  levels increased from an estimated 400–600 ppmv (parts per million by volume) to over 2,500 ppmv, with some estimates suggesting levels up to 8,000 or even 10,000 ppmv during the peak of the crisis.
• Estimated Range: Studies generally cite a 4-fold to 6-fold increase, rising from late Permian background levels to over 2,500 ppmv in the Early Triassic.
• Duration: The sharp increase in
  
  occurred over a relatively short geological time span of about 75,000 years. 

Temperature

• Global Warming: Temperatures rose by 5–10°C, leading to a "hothouse" climate.
• Sea Surface Temperatures (SST): Tropical sea surface temperatures rose to approximately 30°C–35°C, with some estimates in the Tethys Ocean reaching as high as 39°C or 40°C.
• Land Temperatures: Surface air temperatures on land reached even higher extremes, with some models suggesting inland temperatures of ~38°C to 41°C

[Paul Klinkman]

I'd like to toss a potential monkey wrench into the theory that water vapor increases the planet's temperature.  I agree that water vapor is a greenhouse gas.  However, I see how the Amazon basin is dark, full of water vapor and high temperatures are perhaps 30 to 35 degrees C, while the Sahara Desert reflects heat back into space and is empty of water vapor, yet temperatures of 50 degrees C are possible.  On the surface, someone would imagine that water vapor cools the planet.

Heat transportation might be one key. When trees transpire water vapor, the process is endothermic.  Next, a mole of water vapor atoms masses far less than a mole of air atoms, so thunderclouds rise to the stratosphere.  In the stratosphere the water condenses, making the stratosphere hotter.  Then heat radiates more effectively back into space from the stratosphere.

Also, clouds change things.

Does my heat transport theory have legs?  If not, why not?  Anyone want to take a shot at it?  I ask open-ended questions.

Yours in Hope,

Paul Klinkman

[John Nissen]

Hi Paul,

You only need to look at the absorption spectrum for the IR thermal energy from the Earth to see that H2O has a significant effect [1].  If anything water vapour absorbs more than half the total IR absorbed.  The CO2 absorbs nearly 100% at a range of frequencies: at these frequencies, increasing CO2 makes no difference.  Increasing CO2 broadens the range of frequencies for absorption: thus the heating effect is highly non-linear.  This could explain the relatively low equilibrium temperature for a 4 to 6-fold increase in CO2 at the end of the Permian.  But the effect is not sufficient to justify as little as the 3C Mike suggests for a doubling, compared to the 16C I calculated without this effect.

BTW, Peter's friend David Wasdell has a much higher equilibrium temperature than the IPCC.  Of course IPCC scientists advocating net zero want people to believe that it will have a stabilising effect on global temperature, so they will advocate for 3C or less.

Cheers, John

[1] https://en.wikipedia.org/wiki/Atmospheric_window

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[Michael MacCracken]

Dear Paul--

Over the Amazon, where it is wet, it will be lower temperature because it takes energy to evaporate water vapor. As water vapor builds us and is trapping IR, the region warms and the air starts to rise. As it rises, it can hold less water vapor, so water vapor condenses and gives up energy to the atmosphere, warming it and causing the air to rise more and rain out more, etc. So, yes, that there is water there does hold down peak temperature, but the air is saturated and so heat index can be way up.

For the Sahara, with air going up elsewhere, air is coming down over the desert from an altitude where most moisture has been rained out when the air rose. So, as it comes down and is compressed, it warms up. With no water vapor, there will be no clouds. So, during the day most of the incoming sunlight reaches the surface and heats things up. There being no water vapor to evaporate, temperatures can get very warm during mid-day, but also, with virtually no water vapor in the atmosphere, so no greenhouse effect and the temperatures can drop at night to quite cool temperatures (even down to the dew point of the boundary layer air below the inversion that was created by the downwelling air. Relative dry air, even if hot, is generally not as uncomfortable--just go in the shade and it is better-- to endure as hot, saturated air. So, yes, temperature is different but would be better if the enthalpy, I think it is, were the comparative measure so it includes the thermal and latent energy content.

Mike MacCracken 

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[Paul Klinkman]

Dear Restorers,

Let's refocus to what I'm asking.  If we had some kind of artificial heat elevator installed up a 5 kilometer tall mountain, would the same quantity of heat that we collected at sea level and and then transported up 5 kilometers disperse into space more quickly, more time-efficiently because our fixed quantity of heat was then radiating out through a thinner insulating blanket, now above 50% of the total column of earth's atmosphere, above 50% of all radiant heat-deflecting  CO2 and H2O molecules?  Heat escapes slowly from sea level into space because of the planet's insulating blanket of insulation, but that same heat should escape more quickly through a thinner air blanket with 50% less insulatimg abilities.  That's the core issue that I pose here.

I've read that in the Amazon, some thunderclouds can reach a height of 15 kilometers.  Storms don't seem to have the same rotational effects precisely on the equator that we might find near, say, the Gulf Coast of the USA.  Is a thundercloud in fact a physical heat elevator?  Ir converts physical heat into latent heat by evaporation, an endothermic reaction, it runs the latent heat up above half of the CO2 and H2O molecules in the troposphere and then it releases this same latent heat with precipitation, an exothermic reaction.  Most of the condensed water droplets soon find their way back down to ground level, and then the cycle repeats.  Is this a heat elevator that cools the Amazon basin's surface and that raises the average temperature in the stratosphere?   

Do you know that the radiative transfers of heat upward in the Amazon basin that you have been focusing upon will overwhelm this physical heat elevator effect, so that we don't need to care about the physical transport of latent heat toward space in our calculations?  Or, has the physical heat transfer issue not been properly considered?

For proof one way or the other, has anyone compared the average temperature in the stratosphere above the Amazon basin with the average temperature in the stratosphere above the Sahara desert?

Yours in Hope,

Paul Klinkman