In the EPA EF reconsideration document there is a section on p62 where they attempt to make the argument that the CO2 endangerment finding would also apply to direct water vapor emissions to the atmosphere, which is (according to them) obviously absurd. But both claims are bogus.
First off, the definition of pollutant in the Clean Air Act (CAA) clearly does include CO2 as well as water vapor. This was the point litigated in Massachusetts v. EPA in 2007:
An air pollutant is defined as any substance, or combination of substances, including physical, chemical, biological, or radioactive matter, that is emitted into or otherwise enters the ambient air and may reasonably be anticipated to cause or contribute to air pollution.
A Hazardous Substance is further defined as one “that can cause or may reasonably be anticipated to cause adverse health or environmental effects“.
So there are two factors to assess. First, is the substance emitted into the air? (Yes, for both CO2 and water vapor). Second, might it be reasonably anticipated to cause adverse effects? (This is precisely the point of the Endangerment Finding process!). Thus it is not self-evidently absurd that water vapor emissions might be regulatable under the CAA, but the issue is whether there is any evidence that these emissions might plausibly have adverse effects.
It’s worth listing some pertinent comparisons between CO2, water vapor and a criteria pollutant like SO2 (which oxidises to SO4), to see the differences:
| Substance | CO2 | SO4/SO2 | Water Vapor (H2O) |
| Perturbation timescale(s) | > 1,000 years | ~ 2 weeks | ~ 10 days |
| Increase over background since 19th Century (%) | > 50% | ~350% (Greenland, 1980) | ~ 4% (since 1979) ~ 9% (estimate since 1900) |
| Anthropogenic direct emissions | ~ 36 GtCO2/yr | ~ 130 MtSO2/yr (1980) | ~ 21 GtH2O/yr |
| Anthropogenic sources | Fossil fuel combustion, deforestation | Sulfur in coal, biomass burning | Irrigation, combustion |
| Attribution of anthropogenic direct sources to atmospheric increase | ~ 90% | 100% | ~ |
| Impact of climate feedbacks | ~ 10% (ocean/soils etc.) | 0 % | ~ |
| Adverse effects of increase | Increased heat waves, sea level rise, etc. | Acid rain, public health, agricultural yield | More intense rainfall, enhanced global warming |
Basically, direct emission of water vapor has only a minimal impact on the increasing water vapor burden (which is the opposite of the case for CO2 and SO2/SO4) (much less than 0.01% of the WV increase of ~9% is plausibly related to direct emissions). Indeed, it’s clear that the vast majority of the increase is due to climate change itself (warming the atmosphere and increasing the saturation vapor pressure). Thus even if direct WV emissions were reduced to zero, that would be counteracted by a mere 0.05ºC 0.00005ºC change in global temperature.
We are not environmental lawyers, so the criteria are likely more subtle than presented, but the case for direct water vapor emissions being a hazard is very weak. If one was interested in reducing the harms associated with increasing water vapor in the atmosphere, one would obviously start with CO2 and the other greenhouse gases that are driving up the temperatures, not with the almost negligible effect of direct WV emissions. However, it is not absurd that one might consider this, but in practice it is not a very sensible idea.
The bottom line however is that the impact of direct WV emissions are totally immaterial to whether CO2 emissions are a hazard and so this discussion in the EPA proposed rule is merely distraction.
Update (Aug 1): We originally overestimated the impact of direct WV emissions on the concentration by a factor of 1000. The correction makes the point of this discussion even stronger.
I believe that both the 2009 finding and the later aircraft finding discuss water vapor, as do the responses to comments in those documents. Pulling language directly from EPA’s own records may have additional weight in the courtroom
My high-level understanding is that, to first order, the concentration of water vapor is a function of temperature – that is why WV is said to be a feedback and not a climate forcing. Thus the only way we realistically *could* regulate WV as a GHG is via existing regulations on other climate-warming GHGs like CO2 that do act as forcing. Is that accurate?
Yes.
It is, of course, a little more complicated than that. Air at sea level is saturated with WV over 6/7 of the planet. As that air rises and cools, the WV condenses to make (a) clouds, which increase the Earth’s albedo, and (b) rain, which returns the water to the oceans (with, sometimes, some detours over land). While it’s in the air as WV, it does contribute to the greenhouse effect.
AlanJ, yes, that’s correct.
exactly! (thanks)
Segalstad finds resident time for CO2 in the atmosphere using isotopes is between 5-10 years and surveyed literature which confirmed this. The claims of long resident times for anthropogenic CO2 by Climate is disputed.
[Response: Almost any statement about climate has been ‘disputed’. One can describe anything as ‘arguble’ because someone has argued about it. None of these things actually change the physics of the situation. People have confused a residence time in the atmosphere of a single molecule o CO2 with the perturbation time for the system many, many times. And they have been wrong every single time. The key issue is that the atmosphere/surface ocean/biosphere is a coupled and rapidly exchanging system. Thus when we add CO2 to the air we are actually adding it to the (larger) coupled system. And the fluxes in and out of the system as a whole (exchange with the deep ocean mainly) are much smaller. That then means that the residence time in the coupled system (defined as the total in the atm/ocean/biosphere divided by the outputs) is much, much longer than the residence time defined by the atmosphere alone. – gavin]
The thing that makes climate science challenging is not so much taking each piece apart to better understand its function, but the necessity of putting it all together to better understand its action in the system as a whole. The interplay between CO2 and H2O(g) is particularly ‘fun.’
url correction – ignore lowerebill.com/link
Use https://consensus.app/questions/how-long-does-co2-remain-in-the-atmosphere/
How long does co2 remain in the atmosphere
Pro Research Analysis by open sidebar
Searched over 200M research papers
Analyzed relevant papers
Atmospheric CO2 Longevity: Understanding Its Persistence
Introduction to CO2 Atmospheric Lifespan
The persistence of carbon dioxide (CO2) in the atmosphere is a critical factor in understanding and mitigating climate change. The longevity of CO2 emissions from fossil fuels and other anthropogenic sources has significant implications for global warming and climate policy.
Long-Term Fate of Anthropogenic CO2
Research indicates that a substantial portion of CO2 emissions remains in the atmosphere for extended periods. Studies using earth-system models have shown that about 75% of CO2 emissions have an average perturbation lifetime of 1800 years, while 25% have lifetimes exceeding 5000 years 1. This suggests that the atmospheric CO2 levels remain elevated for much longer than previously estimated by other studies, which proposed lifetimes of 300-400 years 1.
Millennial-Scale Atmospheric Lifetime
The notion that the climate impacts of fossil fuel CO2 release persist only for a few centuries is widely held but incorrect. A significant fraction of fossil fuel CO2, ranging from 20-60%, remains airborne for a thousand years or longer 2. The ultimate recovery of CO2 from the atmosphere occurs over hundreds of thousands of years, comparable to the longevity associated with nuclear waste 2. This long tail of CO2 presence in the atmosphere underscores the enduring impact of current emissions on future climate conditions.
Reply to Edmund Esterbauer
For those demanding a thorough technically informed treatment, they should take the trouble to read your posts carefully. Those who are ‘skeptical’ (mostly disingenuously, as they are eager to disable any progress we could and should make to alleviate all our futures, which is not true skepticism: bias is closed-minded) might learn something.
More generally, I did some very hard work in the late ’90s and aughts, since my maths are insufficient, satisfying myself of the conclusions of honest science and vast amounts of evidence plain to anyone paying attention to world weather and data. Once that was done, I didn’t need to go back over it each and every time to convince some self-designated ‘skeptic’ that the knowledge accumulating over time confirmed the obvious: climate change and toxic waste are accelerating. The predictions have been conservative right down the line.
Sadly, these fake skeptics are ably assisted by ‘doomers’ who scream loudly that we’re even more messed up than we thought we were. They seem to have no plan other than to post ragebait, get us to fight each other, and satisfy their egos that anybody but them is ignorant.
Demands for detailed deconstruction of each bit of evidence are a tried and true tactic of those wishing to cast doubt. Sadly, they themselves lack doubt. Otherwise, they’d notice the world all around them.
Nicely put, Roger. Comments like Mr. Esterbauer’s seem aimed at newcomers to climate science. Many RC regulars are educated, formally and otherwise, enough to understand how scientifically robust the conclusion of anthropogenic climate change is. Two centuries after Fourier’s recognition of the atmospheric heat trap, we see vast amounts of evidence yet accumulating, on multiple consilient lines. We know AGW isn’t a house of cards, to be brought down by a single ugly alleged fact. We’re inoculated against denialist arguments from ignorance. There’s no lapsing back!
Alas, those unacquainted with climate science are more susceptible to random specious objections. One hopes Dr. Schmidt’s response is acknowledged as coming from the most qualified source. Thank you, Gavin!
In Re to MalAdapted, 6 Aug 2025 at 10:20 AM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-837075
Sir,
I am afraid that you have missed that “Roger” is someone who copied almost the entire text from the post published by Susan Anderson on 4 Aug 2025 at 10:51 AM in another thread,
https://www.realclimate.org/index.php/archives/2025/07/the-endangerment-of-the-endangerment-finding/#comment-836940 ,
and published it herein as his/her/its own text?
It is the same dishonest and shameful behaviour that I noticed in another post, of 4 Aug 2025 at 8:04 PM,
https://www.realclimate.org/index.php/archives/2025/07/the-endangerment-of-the-endangerment-finding/#comment-836983
wherein someone under nick “GilbertD” copy-pasted my text from another thread, analogously as in the present case.
I suppose that despite different nicks, it is in fact the same unknown entity who started playing a further strange game with readers and moderators of the Real Climate website. I suppose that if you were aware that you are in fact replying to a cheat, you would not like playing with, would you?
Best regards
Tomáš
hi Roger:
It looks like you quoted a lot of my comment here (Mal, please note):
https://www.realclimate.org/index.php/archives/2025/07/the-endangerment-of-the-endangerment-finding/#comment-836940
I wrote that, it’s definitely my work. It was in a response to Atomsk’s Sanakan. I think it would be a good idea to provide an attribution when you quote someone, if it is you who did this.
It’s also possible it doesn’t apply exactly enough to contextualize it to M. Esterbauer.
I’m glad you liked it and related to it enough to use it, but still …
in Re to Susan Anderson, 6 Aug 2025 at 1:10 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-837083
Dear Susan,
I see a similarity between “Roger” stealing your text and “Pedro Prieto” allegedly “paying homage” to the real Pedro Prieto by pretending his identity.
I’m afraid that, due to your infinite kindness, you will disagree with me, but I think that the same entity flooding Real Climate discussions with professionally crafted half-truths that Piotr aptly named “multitroll” has simply invented a new way to cheat and/or ridicule other contributors and moderators of this website.
By the way, “Roger” tested this trick on the same day as “GilbertD”, namely on 4 Aug 2025 at 8:07 PM,
https://www.realclimate.org/index.php/archives/2025/07/the-endangerment-of-the-endangerment-finding/#comment-836987 ,
by posting (without any hint that it is not his/her/its text), as a “reply to Piotr”, Piotr’s own post of 4 Aug 2025 at 1:59 PM from another thread
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836950
Do you think that these coincidences are purely accidental?
Best regards
Tomáš
TK: Thanks, it does feel a bit bot like, but I’m deeply uninterested. Content is what matters. Both PP and Piotr have hostile affects which interfere with their content. I find Piotr more scientifically accurate, and I resent people using this comment section as a vanity publication vehicle, especially when they attack the hardworking, intelligent, and wise people whose guests they are.
My issue with you, poorly expressed and researched I admit, is that you could find more information for yourself if you tried harder.
All: Moving on, I rather liked this cartoon – https://www.theguardian.com/commentisfree/picture/2025/aug/07/how-the-tech-industry-wants-you-to-think-about-ai – which I transcribe here:
“If you ignore the job losses, intellectual property theft, huge environmental costs, disinformation & the fact that it’s making some of the biggest jerks on earth brain-bendingly rich, it really will be a boon for humanity.
Tomas Kalisz, some of your questions on the water cycle are interesting but quite complex. Perhaps you should ask an AI tool like chatgtp or google gemini. Just phrase the question very carefully and clearly. AI is good at searching relevant studies very quickly. If something is there the AI tool will find it quicker than us, and figure out if it supports the theme of your question. Its not infallible by a long way but at the very least you could get a relevant list of studies.
Thanks for your response on the humidity issue. I get it now.
in Re to nigelj, 7 Aug 2025 at 8:22 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-837153
Hallo Nigel,
Thank you very much for your feedback.
Following your advice, I started a step-by-step check of the extent in which I missed easily available climate science information circulating in the public space, for what I am frequently criticized by many regular Real Climate commenters.
As the first step, I tried to check with the AI tool Perplexity how relevant can be my feeling that
– the possibility of equilibrium climate sensitivity (ECS) changes due to anthropogenic interferences with land hydrology
has not been studied yet.
I went through four consecutive question-answer rounds. The obtained output including references provided by the searching engine is attached below.
I would say that on the first sight, it appears that my above-mentioned feeling was wrong, because easily accessible public information suggests that
– studies showing that climate sensitivity is not a constant but depends on the initial state of the climate system do exist and are cited in the IPCC assessment reports,
– the idea that better fit of medium-sensitivity models with previous climate and of the “hot” models with present climate could be explained by changing climate sensitivity looks obvious, because there are hints that climate system state (and feedback processes that may influence climate sensitivity) may have changed, and
– land hydrology including water availability for evaporation belongs to parameters defining the climate system state.
Nevertheless, an inspection of the provided references revealed that none of documents suggested by the engine deals specifically with the relationship between water availability for evaporation from the land and climate sensitivity.
I would therefore conclude that although my question to moderators, regarding feasibility of a study directed to clarification of this relationship, seems to be obvious in view of the publicly accessible information, it appears that there is not easily accessible information in the public domain yet, suggesting that this is already a resolved problem or a subject of an ongoing scientific research or discussion.
Thus, my feeling that this relationship may be still an open scientific problem can be correct, and if so, my question to moderators about feasibility of a modelling study for clarifying the problem may be indeed relevant.
Greetings
Tomáš
————————–
The record of my search follows
Q1:
In climate science discussions, there often appear disputes about so called “equilibrium climate sensitivity” (ECS) that is usually defined as the increase “delta T” of the global mean surface temperature (GMST) which brings a sudden Earth energy imbalance (EEI) caused by a hypothetical abrupt change of a certain climate “forcing” (usually doubling of the atmospheric carbon dioxide concentration).
It appears that although there are publications asserting high climate sensitivity towards atmospheric CO2 concentration changes (more than 5 K for CO2 concentration doubling) also from paleoclimate data, in the mainstream climate science (represented e.g. by the director of the NASA Goddard Institute for Space Studies Gavin Schmidt) prevails a consensus that paleoclimate data suggest rather a medium climate sensitivity (about 3 K for CO2 concentration doubling) and it further appears that this consensus is in accordance with prevailing results of global climate models assessed in the Climate Model Intercomparison Project (CMIP).
Is this understanding right, or do you have a correction?
A:
Your understanding of equilibrium climate sensitivity (ECS) in climate science discussions is largely correct with some nuanced context.
ECS is defined as the long-term increase in global mean surface temperature (GMST) resulting from a doubling of atmospheric carbon dioxide (CO2) concentration. It reflects the climate system’s response once it reaches equilibrium after the forcing change.
There is indeed a range of estimates of ECS in the scientific community:
1. Mainstream consensus:
o Many climate scientists, including Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, support a medium-range ECS estimate around 3 K (degrees Celsius) for CO2 doubling.
o Schmidt and colleagues highlight that recent assessments have narrowed the uncertainty range roughly to 2.6 to 3.9 K.
o This consensus aligns with the frequent range reported by the Intergovernmental Panel on Climate Change (IPCC) and prevailing results from global climate models assessed in the Climate Model Intercomparison Project phases (CMIP5 and CMIP6).
o The broader and more detailed assessments recognize that while ECS is not extremely low, it is also not so high as to foreclose the possibility of mitigation or adaptation.[1][2][3]
2. Paleoclimate data and ECS:
o Paleoclimate records, which study past climates using proxies like ice cores and sediment records, generally support ECS estimates within the traditional range of about 2 to 5 K.
o Paleoclimate studies confirm medium sensitivities and provide valuable constraints that reinforce the validity of climate model estimates.
o Some individual studies have suggested higher ECS values (above 5 K), particularly when interpreting certain warm paleoclimates or specific proxy data.
o However, these higher estimates are not the prevailing consensus and are often more uncertain due to complexities in interpreting ancient climate states.
o Recent research highlights that the newest CMIP6 climate models produce a somewhat broader range of ECS values, including some higher values than previous generations, but many of these high sensitivities are still being evaluated against paleoclimate evidence and observational data to confirm their realism.[4][5][6][7][8]
3. Climate models and ECS:
o CMIP5 models tended to cluster around ECS estimates of 2 to 4.5 K, with an average near 3.2 K.
o CMIP6 models have introduced some that simulate notably higher climate sensitivities, sometimes exceeding 5 K.
o This increase in modeled sensitivities has prompted intense research to understand whether these higher values are realistic or reflect model biases, especially concerning cloud feedbacks.
o Overall, even with some high ECS values in CMIP6 models, the ensemble mean and best estimates remain close to the medium sensitivity range, consistent with paleoclimate and observational constraints.[9][10][11]
In summary, the prevailing mainstream scientific view, including that articulated by Gavin Schmidt and supported by major climate modeling intercomparison projects, holds that Earth’s equilibrium climate sensitivity likely lies near 3 K, with a range roughly between 2.5 to 4 K for doubled CO2. Paleoclimate data broadly support this medium range, though high ECS estimates do exist in some studies. CMIP6 models have introduced somewhat higher ECS values, which are under active investigation. This nuanced consensus balances multiple lines of evidence and acknowledges uncertainty, but does not embrace the highest ECS estimates as the dominant view at this time.
Hence, your summary is accurate: the mainstream scientific consensus supports a moderate climate sensitivity of about 3 K for CO2 doubling, consistent with paleoclimate data and the majority of climate model results, despite some research suggesting higher values in certain cases.
⁂
1. https://science.nasa.gov/earth/climate-change/making-sense-of-climate-sensitivity/
2. https://www.carbonbrief.org/the-carbon-brief-interview-dr-gavin-schmidt/
3. https://en.wikipedia.org/wiki/Climate_sensitivity
4. https://psa2022.dryfta.com/program-schedule/program/detail/141/climate-sensitivity-paleoclimate-data-amp-the-end-of-model-democracy
5. https://link.springer.com/article/10.1007/BF00143708
6. https://www.nature.com/articles/s41612-025-00948-7
7. https://www.nature.com/articles/s41558-020-0764-6
8. https://www.nature.com/articles/s43247-024-01531-3
9. https://skepticalscience.com/gwpf-lewis-crock-climate-sensitivity-optimism-ill-founded.html
10. https://www.carbonbrief.org/cmip6-the-next-generation-of-climate-models-explained/
11. https://ukesm.ac.uk/climate-sensitivity-in-cmip6-causes-consequences-and-uses/
Q2:
In the above-mentioned climate science discussions, I have noticed a remark that the “hot” models of the CMIP6, suggesting high climate sensitivity, do appear to fit better (in comparison with the entire CMIP6 ensemble and/or with the CMIP5 models) the present climate change as observed in the last decades.
The mainstream scientists, however, are still reluctant to accept that the “hot” models should be preferred, because they do not fit the paleoclimate data as good as the “conservative” models with medium ECS.
Is it true?
If so, could I rightly conclude that in view of the present knowledge, climate models with medium climate sensitivity do fit paleoclimate data well but somewhat struggle with the present climate change, whereas the “hot” models with higher climate sensitivity seem to fit the present climate change better, however, they still seem to struggle with paleoclimate data?
A:
Your understanding is largely accurate and reflects the current nuanced discourse within climate science regarding the CMIP6 “hot” models and their climate sensitivities.
1. The “hot” models within the CMIP6 ensemble are those with relatively high equilibrium climate sensitivity (ECS), often above the upper end of the IPCC likely range of about 4 K, with some models showing ECS values exceeding 5 K. These models generally produce stronger warming projections for the present and future climate compared to the broader CMIP6 ensemble or the earlier CMIP5 models.
2. Recent studies and assessments indicate that these “hot” models tend to fit observed recent climate changes over the past decades somewhat better than models with medium ECS, particularly with respect to the magnitude of warming observed so far. This is likely why they attract attention for their apparent better agreement with the present-day warming trend.
3. However, mainstream climate scientists remain cautious about favoring the “hot” models due to their poorer fit to paleoclimate data. Multiple paleoclimate studies have found that models with very high ECS values simulate temperatures for past climate states (such as the Last Glacial Maximum or warmer greenhouse periods) that fall outside the ranges indicated by proxy data, suggesting those models may overestimate climate sensitivity.
4. Meanwhile, models with medium ECS (roughly 2.5 to 4 K) tend to perform well in reproducing paleoclimate conditions, providing a consistent and physically plausible picture across a wide range of past and present climate data.
5. The disagreement primarily arises because the constraints from paleoclimate and the constraints from recent instrumental observations and short-term variability sometimes pull the estimates towards slightly different sensitivities. The “hot” models, with stronger warming, appear more consistent with recent trends but less so with paleoclimate evidence, while the medium-sensitivity models are well aligned with paleoclimate but somewhat less aggressive in simulating recent warming magnitude.
6. This tension leads to approaches where the “hot” models are either down-weighted or combined with other models using sophisticated statistical methods (e.g., Bayesian model averaging) to produce balanced future projections that account for both sets of evidence, rather than outright rejecting either group.
In conclusion, yes, you can rightly sum up that:
• Climate models with medium climate sensitivity fit paleoclimate data well but may somewhat underestimate or struggle to fully capture the magnitude of observed recent climate change.
• The “hot” CMIP6 models with higher climate sensitivity tend to fit present climate change observations better but struggle more with paleoclimate constraints.
This ongoing evaluation reflects the complexity of climate system responses and the importance of integrating multiple lines of evidence to understand and project future climate.[1][2][3][4][5][6]
1. https://hess.copernicus.org/preprints/hess-2023-47/hess-2023-47.pdf
2. https://hess.copernicus.org/articles/27/4355/2023/
3. https://www.nature.com/articles/s43247-023-01009-8
4. http://su.diva-portal.org/smash/record.jsf?pid=diva2%3A1921490
5. https://www.nature.com/articles/s43247-024-01531-3
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC11041668/
Q3:
Is there a scientific publication or another article or blog discussing the possibility that both “traditional” climate models fitting better the past climate and the “hot” models fitting better the present climate could be right if the present climate sensitivity is higher than the climate sensitivity in the past?
A:
Yes, there are scientific publications discussing the possibility that both “traditional” climate models, which better fit past climate, and “hot” climate models, which fit better the present climate, could be correct if the climate sensitivity has changed over time—specifically if the present climate sensitivity is higher than it was in the past.
Key points from the literature include:
• Climate sensitivity estimates from past climate changes and from modern observations may differ because feedback strengths and forcing timescales vary over time. For example, slow and fast feedback processes (like ocean heat uptake and ice sheet changes) may influence sensitivity differently in past versus present climates, leading to timescale-dependent or state-dependent climate sensitivity.[1]
• Models sometimes show that the present climate’s feedbacks (such as cloud behavior and water vapor feedback) and the base state of the climate system differ substantially from those in past climate states, potentially causing a higher effective climate sensitivity now than during earlier periods.[2]
• Some studies from paleoclimate and observational data suggest that the climate system response is non-stationary and dependent on background climate states and timescales, making it plausible for climate sensitivity to vary with time.[1]
• This understanding helps reconcile why some climate models aligned well with past climate changes but underpredict observed warming in recent decades whereas “hot” models with higher sensitivity better match current warming trends.[2][1]
• The IPCC and related research emphasize uncertainties in cloud feedbacks and other processes that contribute to different effective sensitivities in models over time, yet allow for models with different sensitivities to both be reasonable representations depending on timescale and epoch.[3][2]
Thus, the scientific community recognizes that climate sensitivity is not necessarily constant over time, and the difference between model fits to past versus present climate can be explained by this variability in sensitivity, making it plausible that both sets of models could be valid under different conditions.
References:
• Roe & Baker (2016) on lessons from past climate changes and time-dependent sensitivity[1]
• IPCC AR4 chapter on model evaluation and feedback differences[2]
• Discussions on climate model strengths, limitations, and feedback uncertainties[3]
⁂
1. https://link.springer.com/article/10.1007/s40641-016-0049-3
2. https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter8-1.pdf
3. https://www.wcrp-climate.org/images/modelling/WGCM/publications/sap3-climate-models.pdf
Q4:
Can you find any article suggesting or discussing possible climate sensitivity change due to a change in water availability for evaporation from the land?
A:
There are scientific articles discussing how changes in water availability for evaporation from the land can influence climate sensitivity or climate feedbacks.
Key points include:
• Climate change affects global water availability through changes in both precipitation and evaporation, which vary by region and season. Changes in evapotranspiration and soil moisture affect surface energy balances and can modulate climate responses. For example, increased evaporation in wetter regions can amplify climate impacts, while in drier regimes water limitation constrains evaporation changes. These changes influence the spatio-temporal distribution of water availability and thus the energy and moisture fluxes that drive climate processes.[1][2][3]
• Increased temperatures can raise evapotranspiration losses, reducing water availability and potentially modifying feedback mechanisms in regional climates. This can make land surface moisture a factor influencing climate sensitivity, as soil moisture and evaporation exert control over land-atmosphere interactions and surface temperature regulation.[4][5]
• Research indicates that models and observations of hydrology reveal that water availability changes due to climate forcing may be more sensitive than previously thought, suggesting a possible revision to how climate feedbacks related to evaporation and moisture are represented. This sensitivity in water availability could imply changes in effective climate sensitivity linked to land surface processes.[6]
While these articles do not always explicitly frame water availability changes as altering the “climate sensitivity” parameter per se, they discuss how changes in evaporation and soil moisture—key elements of land hydrology—influence climate feedbacks and thereby could contribute to variability in climate sensitivity over time or regions.
In summary, there is scientific discussion and evidence supporting the idea that changes in land water availability for evaporation can affect climate system feedbacks, thus potentially playing a role in changes in climate sensitivity.
References:
• Nature Communications article on changes in water availability through precipitation and evaporation under climate change.[2][1]
• Regional studies on evapotranspiration increases reducing water availability and influencing climate feedbacks.[5][4]
• Hydrological analyses suggesting higher sensitivity of water availability to climate parameters than previously accounted for.[6]
• Recent reviews of multifaceted water availability changes impacting climate dynamics.[3]
⁂
1. https://www.nature.com/articles/s41467-020-16757-w
2. https://www.sciencedirect.com/science/article/pii/S1674283424000862
3. https://www.nature.com/articles/s41612-025-00913-4
4. https://link.springer.com/article/10.1007/s10584-021-03122-z
5. https://hess.copernicus.org/articles/21/2107/2017/hess-21-2107-2017.pdf
6. https://smartwatermagazine.com/news/h2o-building-services/how-climate-change-impacts-water-availability-systematically
Oh dear. I apologize for overlooking your comment on the other thread, Susan. I haven’t been paying close attention to RC lately, spending my time on Zeke and Andrew’s blog instead. I’m sure it’s annoying to see yourself plagiarized. It’s certainly weird. Roger might actually be some kind of AI agent. My approbation of Roger’s comment should go to you. My point about Edmund Esterbauer’s comment and Gavin’s inline response stands, nonetheless. Indeed, you’re my exemplar of the educated layperson, who knows too much about climate science to be misled by random obstructionists!
Regardless of temperature or other environmental conditions, automobiles (and other ICE vehicles) emit both CO2 and water vapor…but also exhaust aerosols. Is it those aerosol emissions that are immediately endangering people, especially in high population density city locations. CO2 and water vapor have been turning the Earth greener. Aerosols are not helping…;polluting. When if? we finish the energy transition to renewables and EVs we will not have that problem, Unfortunately we can’t complete the transition without those vehicles. A rock and a hard place?
“A rock and a hard place?”
As discussed previously, nope. Since previous explanations haven’t worked for you, try it this way: Your metaphorical formulation makes the “rock” of maximal climate disruption (due to the hypothetical non-replacement of ICE vehicles) equivalent to the “hard place” (of replacement of ICE vehicles with all practicable speed)–obviously a logical absurdity.
KT: CO2 and water vapor have been turning the Earth greener.
BPL: Look again:
https://www.scientificamerican.com/article/earth-stopped-getting-greener-20-years-ago/
I thought the atmosphere had more water vapour, meaning higher absolute humidity as a result of global warming while the link you posted says there’s an increasing vapour pressure deficit. This seems like contradiction. What am ‘I missing here?
In Re to nigelj, 2 Aug 2025 at 6:29 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836847
Hallo Nigel,
The article cited by Barton speaks about relative humidity, which indeed decreases as the Earth warms.
Greetings
Tomáš
KT: CO2 and water vapor have been turning the Earth greener.
BPL: Look again.
https://www.scientificamerican.com/article/earth-stopped-getting-greener-20-years-ago/
Ken – “Is it those aerosol emissions that are immediately endangering people, especially in high population density city locations. CO2 and water vapor have been turning the Earth greener.”
The “greening” statement is kind of meaningless, but also falsely triggers positive, ‘green’, emotional response. The SARS-CoV-2 virus ‘cleaned the air’ in 2020, but does “pandemics clean the air” sound good to you given the full context?
In my high population density city location, air quality has taken a nose dive for many days in a row now, including some days in Unhealthy territory according to the airnow.gov charts. Not from cars, but mostly from the massive wildfires in boreal forests in Canada’s north. People under the smoke are immediately endangered because of the CO2 that’s been rapidly warming the high latitude forests and frozen peatlands. If this is ‘greening’, we need less of it, please.
At 8:00am CDT on August 4th, Chicago’s air quality is ‘Unhealthy for sensitive groups’, but in Poy Sippi Wisconsin, it’s Unhealthy, and more people live in my building in Chicago than live in all of Poy Sippi, Wisconsin.
in Re to b fagan, 4 Aug 2025 at 8:30 AM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836933
Sir,
Referring to John Pollack, 1 Aug 2025 at 10:05 PM,
https://www.realclimate.org/index.php/archives/2025/08/unforced-variations-aug-2025/#comment-836805
I am quite curious if the present wildfires affect more
a) untouched natural ecosystems (despite their high beaver population and an unaltered hydrology regime),
b) economically unexploited quasi-natural forests with an altered hydrology due to eradication of their original beaver population,
c) plantation forests cultivated for wood production. or
d) all of them, irrespective of their ecosystem diversity and their hydrological regime.
Is this question asked or discussed in media reporting on the wildfires?
Greetings
Tomáš
Hello Tomáš,
Your Q: “Is this question asked or discussed in media reporting on the wildfires?”
If you wish to survey media reports to get the answers to your questions, the media is at your fingertips, so happy hunting! For the fires that continue to provide lowered air quality in my region, here’s a start to their current locations, and you can then start digging into the local reporting if that’s got you curious. https://cwfis.cfs.nrcan.gc.ca/interactive-map
My guess is wildfires will continue to become more common in most places where there is fuel and fire conditions, due to our rapidly-warming climate, like up in the boreal forests right now. Enjoy your research.
Regards
b fagan
Ken (and for readers at large) –
How much ‘greening’ is vegetation recovery after centuries of de-vegetation? Without that longer term comparison – and most claims of CO2 greening I’ve encountered don’t do that and rely on shorter, more recent timelines – it isn’t clear how much is simply vegetation recovery. (Note, not all plant species recover – it isn’t true restoration, which is unlikely to persist even when we try because… global warming.)
It does look like a lot of re-vegetation is a consequence of more productive agriculture allowing some agricultural land to lapse into re-vegetation. Some ‘greening’ is from reduced snow cover and warmer, longer growing seasons in cold climate regions.
Whether wetter conditions in some regions contribute more ‘greening’ than losses from increased aridity in others is also a question – taking higher water vapor content to reach the saturation needed to rain at all is the flip side of the ‘warmer air holds more water vapor/causes heavier rainfall’ response to raised GHG’s.
I think the ‘but we need fossil fuels to make EV’s’ argument is specious; yes, we start from where we are and like with internal combustion traction engines what came before (steam engines) helped make what went on to displace steam traction engines. We would struggle to commence the transition without resort to fossil fuels but completing the transition will be done without them.
Dear moderators,
I appreciate that you opened this topic pertaining to the role of water in Earth climate, although with a narrow (and in my opinion somewhat unfortunate) focus on anthropogenic “water vapour emissions”.
1) I put this framing in quotes because I think that reduction of anthropogenic interferences with global water cycle and especially with land hydrology to “anthropogenic water vapour emissions” is neither possible nor reasonable.
2) I am afraid that discussing ” water emissions” from fuel combustion, irrigation (or, e.g. laundry drying :-)) without considering possible (and in my opinion possibly quite significant) “negative emissions” may be seriously misleading. There may be, and likely were, many possible sources of a such “negative emissions”, for example: soil destruction, land deforestation, wetland drying, landscape drainage by agricultural meliorations, by river regulations and by building infrastructure that prevents soaking and speeds up runoff.
3) In view of the circumstance that these “negative emissions” were not mentioned in your post, I am somewhat afraid that they were not considered in the attribution of 4% of the “increase over background” (Do you mean an increase in average global absolute air humidity?) to “direct anthropogenic sources”. If so, the attribution would have been very questionable already for this single reason.
4) Moreover, I have a feeling that your post omitted the hint that changes in latent heat flux accompanying “positive” or “negative” “water vapour emissions” could have a significant influence on mean global surface temperature (GMST). As suggest results of a modelling study published by Lague et al
https://iopscience.iop.org/article/10.1088/1748-9326/acdbe1 ,
prevailing “positive” emissions might cool Earth surface and paradoxically result in global average absolute air humidity decrease, due to lowering water vapour supply from the ocean. Oppositely, in their “desert land” scenario, lowering water supply from land resulted in a GMST increase that caused global increase in the average absolute air humidity.
5) In view of the preceding remarks, I doubt that discussing “water vapour” merely as a possible source of greenhouse effect makes a sense. I am afraid that clouds and latent heat flux (both also playing a significant role in Earth surface temperature regulation) are so intricately combined with water vapour formation that all these mechanisms of Earth climate regulation cannot be assessed separately from each other.
6) For all the above reasons, I respectfully disagree with you opinion that (although it is not worth of the effort, because anthropogenic “direct water vapour emissions” are allegedly small in comparison with “water vapour feedback” to other anthropogenic climate forcings), “water vapour” could be, at least “in principle”, legally treated as an air pollutant, the same way as other anthropogenic air pollutants, including carbon dioxide.
7) I think that due to above mentioned complexity, water vapour is significantly different from all other pollutants. I am afraid that even a suggestion that it COULD be legally treated the same way as other pollutants is potentially dangerous, because it may be highly confusing for broad public and it might easily cause a huge legal turmoil.
Could you comment?
Best regards
Tomáš
Tomas: “Dear moderators, I appreciate that you opened this topic pertaining to the role of water in Earth climate,”
Tomas never misses a chance to miss the point. NOBODY is “opening” on the role of water – if anything the opposite – moderators point that why direct changes to WV emissions are IRRELEVANT to AGW:
CO2 SO4/SO2 Water vapour
Perturbation timescale(s) > 1,000 years ~ 2 weeks ~ 10 days
Increase over background
since 19th Century (%) > 50% ~350% ~ 4% (since 1979), ~ 9% (since 1900)
And even that ~9% is NOT as a result of “direct” changes in WV emissions, but “indirect” result of increasing T, thanks to CO2 increase.
And therefore moderators do NOT “open” it as a worthwhile subject, but identify WV as a disingenuous distraction from the crucial role of GHGs, I quote:
“The bottom line however is that the impact of direct WV emissions are totally immaterial to whether CO2 emissions are a hazard and so this discussion in the EPA proposed rule is merely distraction.”
It applies to the actions of the climate change deniers from the EPA, as it applies to you, JCM and other “anything but GHG” deniers..
in Re to Piotr, 1 Aug 2025 at 1:21 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836774
Hallo Piotr,
It is indeed possible that the moderators (Am I right that the term “Group” means all of them?) merely wanted to emphasize that anthropogenic “direct water vapour emissions” are irrelevant to the observed global warming. Nevertheless, I still think that the value of their post “Are direct water vapor emissions endangering anyone?” may rather than in their message alone consist in the circumstance that it generally pertains to the role of water in Earth climate and thus offers an opportunity to discuss this important (but in my opinion still quite underrated) topic.
If you read my post, you could recognize that I do rather question the basis of their message (the method how the emissions were estimated) as the message (that “direct changes to WV emissions are IRRELEVANT to AGW”) itself.
I strived to show that despite the direct greenhouse effect of “anthropogenic water vapour emissions” can be unimportant, it is still well possible that human interferences with water cycle could have contributed to the observed global climate change significantly. That is why I expressed a concern that the narrow focus on “vapour emissions” without putting them into the respective complex context may rather mislead the broad public than educate it.
Greetings
Tomáš
The latest example: this thread:
– climate scientists: direct WV emissions are insignificant to AGW, and are used by the deniers as a distraction from the urdency to reduce GHGs
– the resident “anything but GHGs” denier Tomas Kalisz: portrays this as the said scientist … supporting his denialism by opening the discussion on the effects of direct WV emissions on AGW, an “important (but in my opinion still quite underrated) topic.”
Can you be any more impervious to arguments and logic, Tomas?
In Re to Piotr, 3 Aug 2025 at 10:25 AM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836877
Hallo Piotr,
It appears that you have not read my posts to that you reply, except the first sentence of the first one.
If you perhaps have, why do you address solely the least substantive sentence and totally neglect the entire context?
Greetings
Tomáš
Tomas Kalisz: “It appears that you have not read my posts to that you reply, except the first sentence of the first one”
Since the rest of your post RESTS on that sentence – it is enough to falsify IT and the rest of your posts becomes a bunch of irrelevant tangents based ON THE FALSE PREMISE.
And to falsify this premise of the presumed importance of human WV changes to AGW its enough to quote the two most relevant to your claim lines from the table in the opening article:
Attribution of anthropogenic direct sources to atmospheric increase:
CO2 ~ 90% Water vapour: 0.004%
Impact of climate feedbacks:
Co2 ~ 10% (ocean/soils etc.) Water vapour: 99.996% (impact of T on saturation vapor pressure)
That’s why direct emissions of WV are COMPLETELY INSIGNIFICANT to AGW, and ANY effect of WV on AGW – is only (99.996%) as a positive FEEDBACK – that PASSIVELY AMPLIFIES the results of our action or inaction on GHG emissions.
And are used by the DENIERS, like those from EPA, JCM and you – as a DISTRACTION from the urgency of reducing GHGs
PS. I capitalized the important words so you can’t pretend that nobody was telling you that.
in Re to Piotr, 4 Aug 2025 at 1:20 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836949
Dear Piotr,
The sentence that you evaluated as a sufficient ground for not reading the rest of my post reads:
“I appreciate that you opened this topic pertaining to the role of water in Earth climate, although with a narrow (and in my opinion somewhat unfortunate) focus on anthropogenic “water vapour emissions”.”
I think that even from this single sentence becomes quite clear that I speak about the role of WATER in Earth climate regulation and that I doubt that this role can be reduced to (greenhouse effect of) water vapour. Furthermore, this sentence is completely silent about anthropogenic global warming (AGW).
Despite it, you assert that I presented a premise of “importance of human WV changes to AGW”. Please read my sentence again and check if there indeed is what you assert.
If you find out that you were wrong and decide to read more, it will be my pleasure to discuss possible further objections that may arise from your side.
Greetings
Tomáš
P.S.
By the way, I think that in the mathematical logic, a valid conclusion does NOT require a valid premise. In other words, a valid implication requires only that the conclusion is valid; it does not prescribe anything for the premise.
Although it may sound or look strange on the first sight, I confirm that it is fully in accordance with my practical experience. During my professional career, I several times met with technically feasible and industrially applicable inventions that arose from utterly incorrect premises.
For these reasons, I think that the popular phrase “garbage in, garbage out” (GIGO, a dismissal of a certain outcome reasoned merely by an obviously invalid premise) may be in fact unjustified / inapplicable as an argument sufficient per se for invalidating someone’s conclusion(s).
Tomas Kalisz: “I think that even from this single sentence becomes quite clear that I speak about the role of WATER in Earth climate regulation
Since you posted
– in the thread about emissions of water vapour,
– in response to the article on emissions of water vapour
– and with your history of promoting for a year (?) your crazy Sahara schemes of increasing emissions of water vapour
this discussion IS about water vapour.
Hence your subsequent demands that climate scientists address your feelings on the importance of the NON-WATER VAPOUR forms of water – are exactly what I’ve jsut described them – “ a bunch of irrelevant tangents”..
Irrelevant to the thread you are posting in, irrelevant to the mitigation of the AGW (as the table shows in the opening thread – your “WATER” is only a feedback, NOT a driver of AGW) and, scientifically irrelevant – your WATER is already implicitely included in the climate models – so there is little to gain by evaluating its role explicitly, as it were an independent forcing.
If YOU want to waste your time on such irrelevant tangent – do it by yourself – but stop demanding that top climate scientists waste their time to keep explaining to you what you are obviously incapable or unwilling to understand.
Now go away or we shall taunt you a second time!
Tomas, this, too, has been discussed already at wearisome length. I’ll only ask you to recall what has been said about residence time of water vapor in the atmosphere–and take note of the related concept given in the table in the OP. To wit: “Perturbation timescale: 10 days”.
In Re to Kevin McKinney, 1 Aug 2025 at 4:43 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836782
Hallo Kevin,
Honestly, I am not aware that the moderators have ever addressed the role of water cycle in Earth climate regulation in its entirety. As I expressed in my parallel reply to Piotr
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836790
I am somewhat surprised by the narrow focus of the present post “Are direct water vapor emissions endangering anyone?” on the “direct anthropogenic water vapour emissions”, because I am afraid that such an extreme narrowing of the extremely complex role of water in Earth climate could be seriously misleading.
Greetings
Tomáš
Your REQUIRE that senior scientist moderators be the ONLY people you will listen to. And then you fail to pay attention to the material they’ve posted for over a decade on the subject.
Please just stop. This site is not a tutorial for your personal benefit. Your responses indicate that you either ignore or fail to understand the material.
The information you need is readily available for a small effort. Your refusal to do the work is no excuse for demanding more attention.
in Re to Susan Anderson., 3 Aug 2025 at 5:54 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836901
Dear Susan,
Honestly, I am not aware of any material published by the moderators on this website that pertains to the role of water in climate regulation in its entirety.
I know Gavin’s post “Water vapour: feedback or forcing?” of 6 Apr 2005,
https://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/,
comprising an update of Oct 2010, with a link to an article
http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?id=sc05400j
that seems to be not operational anymore.
To check if I missed anything, I searched for the article, found it under
https://www.giss.nasa.gov/pubs/docs/2010/2010_Schmidt_sc05400j.pdf
and read it again.
It seems to be completely silent about latent heat flux. I therefore think that it indeed deals with greenhouse effect of water vapour only, somehow combined with greenhouse effect of clouds, in accordance with the abstract of the article that reads
“The relative contributions of atmospheric long‐wave absorbers to the present‐day
global greenhouse effect are among the most misquoted statistics in public discussions
of climate change. Much of the interest in these values is however due to an implicit
assumption that these contributions are directly relevant for the question of climate
sensitivity. Motivated by the need for a clear reference for this issue, we review the
existing literature and use the Goddard Institute for Space Studies ModelE radiation
module to provide an overview of the role of each absorber at the present‐day and under
doubled CO2. With a straightforward scheme for allocating overlaps, we find that water
vapor is the dominant contributor (∼50% of the effect), followed by clouds (∼25%)
and then CO2 with ∼20%. All other absorbers play only minor roles. In a doubled CO2
scenario, this allocation is essentially unchanged, even though the magnitude of the total
greenhouse effect is significantly larger than the initial radiative forcing, underscoring
the importance of feedbacks from water vapor and clouds to climate sensitivity.”
In my posts, I objected primarily that the recent article “Are direct water vapor emissions endangering anyone?” may be confusing for the broad public, because it ignores the role of latent heat flux again and narrows the role of water in climate regulation even more than the 2005 article, namely to the greenhouse effect of water vapour only.
I cannot exclude that I still missed another Real Climate post by moderators, clarifying why the role of latent heat flux in climate regulation does not deserve their attention. If you know the respective explanation, I will be very grateful therefor (or for a specific reference thereto).
Sincerely
Tomáš
Yes the pollution framing of realclimates could be misleading when it comes to hydrological cycling and latent flux. Phony environmentalists frequently use this framing to minimize the importance of conservation stewardship. They knowingly and actively distort the issue. Increasing WV residence time and saturation vapor pressure is a response to environmental desruction. This is distinct from direct emission. Currently working in UK and will be back in a couple weeks. Cheers
Direct water vapor emissions from ICE vehicles include CO2, some carbon monoxide and aerosols. The exhaust aerosols can be dangerous to anyone inhaling them. Especially joggers running roadsides in high traffic areas.
Ken Towe: “ Direct water vapor emissions from ICE vehicles include CO2, some carbon monoxide and aerosols.
Huh? This has as much sense as saying that the exports of potatoes include oranges, some apples and pineapples.
Thank you. However, vegetables and fruits emit water vapor when cooked. But no aerosols that can be dangerous.
Ken Towe: “However, vegetables and fruits emit water vapor when cooked.”
So does apparently your brain, when the absurdity of your claim:
Direct water vapor emissions from ICE vehicles include CO2, some carbon monoxide and aerosols” (c) Ken Towe
has been pointed out.
Personal insults seem to be your anonymous response to anyone with whom you disagree.. Are you denying that exhaust vapors do not contain direct water and CO2 (plus aerosols)?
Ken Towe 3 Aug: “ Are you denying that exhaust vapors do not contain direct water and CO2 (plus aerosols)?”
Trying to change the original post after the fact, Ken? That’s what you really wrote:
“ Direct water vapor emissions from ICE vehicles include CO2, some carbon monoxide and aerosols.” (c) Ken Towe.
So you DIDN’T write that the “ exhaust vapours include”, you DID write “ water vapor emissions include CO2, CO, and aerosols”.
Thus what you actually DID write – has no sense, as water vapour includes water vapour, NOT “CO2, CO, and aerosols”, hence my FIRST response:
P: “Huh? This has as much sense as saying that the exports of potatoes include oranges, some apples and pineapples.”
Since my appeal to your intelligence has obviously failed – see your “reply”:
– KT: “vegetables and fruits emit water vapor when cooked”
I concluded with calling spade the spade:
P: “So does apparently your brain, when the absurdity of your claim has been pointed out”
To which you CHANGE what you originally said, and based on that change- portray my response as baseless “personal insults” ??? Ken Towe – everyone!
LINK- EPA EF reconsideration document, don’t work
[Response: Fixed. ]
The Inflation Reduction Act has amended the Clean Air Act to included GHG as pollutants but specifically excluded water vapor. It had to do so in a way that allowed them to get it in budget legislation, which gives some room to legally get around it, but the authors of the IRA crafted it in a way to make that difficult,
A law journal article discussing it is here:
https://www.eli.org/sites/default/files/files-pdf/53.10017.pdf
The attempt to remove the endangerment finding is subject to legal challenge and as it is written will probably not survive one. It looks more like a lawsuit brought in a civil court that does not have much merit but will cost the defendant time and money to answer. It is harassment to coerce something from or harm the defendant.
The current president was well known for this. That legal strategy will go nowhere in the courts reviewing this or with the parties (state governments, clean energy producers, and NGOs.) who will challenge it.
Or you could no longer invent biased claims without any cited evidence. The sea level rise (SLR) acceleration is statistically significant. It also appears in longer-term data that extends before the post-1993 satellite era. You were already shown that, despite you not engaging with the evidence:
– https://web.archive.org/web/20250803204724if_/https://pbs.twimg.com/media/Gd9NhhJW0AAS_G_?format=png&name=small
[ https://doi.org/10.1175/JCLI-D-17-0502.1 ]
– “We estimate the acceleration of the GMSL rise to 0.12 ± 0.05 m yr−2 which confirms previous analysis in the literature demonstrating that the GMSL record is accelerating”
https://doi.org/10.5194/os-19-431-2023
SLR acceleration was already predicted as a result of anthropogenic forcing and is already factored into mainstream SLR projections:
– IPCC AR6: “GMSL rise has accelerated since the late 1960s, with an average rate of 2.3 [1.6 to 3.1] mm yr–1 over the period 1971–2018 increasing to 3.7 [3.2 to 4.2] mm yr–1 over the period 2006–2018 (high confidence) [page 1216].”
https://web.archive.org/web/20220507074626/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf
– IPCC AR6: figure 9.27
https://web.archive.org/web/20250516003359im_/https://www.ipcc.ch/report/ar6/wg1/downloads/figures/IPCC_AR6_WGI_Figure_9_27.png
[ https://web.archive.org/web/20250516003359/https://www.ipcc.ch/report/ar6/wg1/figures/chapter-9/figure-9-27 ]
The folks peddling natural oscillations as a main cause instead predicted SLR deceleration. They were wrong. I suggest you stop following them just to suit a preconceived bias against anthropogenic attribution, or a Curry-like desire to exaggerate uncertainty / manufacture false doubt. You should instead reflect on what’s wrong with their ‘natural oscillations’ hypothesis:
– Gervais 2016: https://web.archive.org/web/20240614033933im_/https://archive.is/gx4VS/9b21827f35c2c28c9d75de40b25e8de2c652a0f7.png
[ https://doi.org/10.1016/j.earscirev.2016.02.005
https://pubpeer.com/publications/00842E8B83919D9CE37E22CDAB003B ]
– Dr. Judith Curry: “Once again, the emerging best explanations for the ‘pause’ in global surface temperatures and the slow down in sea level rise bring into question the explanations for the rise in both in the last quarter of the 20th century. And makes the 21st century of sea level rise projections seem like unjustified arm waving.”
https://web.archive.org/web/20240312184206/https://judithcurry.com/2014/04/24/slowing-sea-level-rise/
– Dr. Javier Vinós: “Regarding sea level rise, we have entered a phase in the 65-yr oscillation that instead of adding to the rise it subtracts from it, and for the first time since 1900 the low in the 65-yr oscillation coincides with a low in solar activity. […] Sea level rise is decelerating for a period of a couple of decades. It will make every expert prediction of 21st century sea level rise completely wrong, except the highly criticized and superseded IPCC B1 scenario.”
https://web.archive.org/web/20250803220143/https://judithcurry.com/2019/02/08/sea-level-rise-whiplash/#comment-889227
– Dr. Matt Ridley: “Sea level is rising at the unthreatening rate about a foot per century and decelerating [pages 4 to 5].”
https://web.archive.org/web/20161024181412/https://www.climateconversation.org.nz/downloads/scientific-heresy-ridley-oct-2011.pdf
– Dr. Matt Ridley: “And you mean the unsteady rise in sea level, decelerating since 2004? See http://joannenova.com.au/2013/11/sea-level-rise-slowed-from-2004-deceleration-not-acceleration-as-co2-rises/ ”
https://archive.is/LMccE
And your bias is evident in what you said elsewhere about climate models ( https://www.realclimate.org/index.php/archives/2025/07/the-endangerment-of-the-endangerment-finding/#comment-836770 ).
Quote: “As shown in Fig. 3, we estimate the GMSL rise over the 29 years of the altimetry record, from January 1993 to December 2021, to 3.3 ± 0.3 m yr−1. We estimate the acceleration of the GMSL rise to 0.12 ± 0.05 m yr−2 which confirms previous analysis in the literature demonstrating that the GMSL record is accelerating”
They got their units wrong. Should be mm, not m. Off by a factor of 1,000.
Fact Checker,
Given they (Guérou et al 2023) are explicitly referencing “Fig. 3” and Fig. 3 in plotting “Global Mean Sea Level [cm]” plainly states “Jan 1993 – Dec 2021, Trend : 3.3 ± 0.3 mm/yr, Acceleration : 3.3 ± 0.3 mm/yr^2“, your fact-checking is pedantic nonsense. This is but a typo, and an obvious one to correct.
Well said. MAR. Was just thinking the same.
Why hasn’t Fact Checker taken Trump to task for his sustained three order of magnitude misrepresentation of seallevel change ?
https://x.com/RussellSeitz/status/1951828199098446034/photo/1
Everyone’s timid in a dictatorship.
A rock and a hard place? No Ken, just a journey that starts with the first step,.continues with the second step, then the third step, and by the nth step you wonder why you ever thought you couldn’t get over that pass into the next valley.
It sounds very much to me like you all are saying the the endangerment finding is moot.
This article seems to confirm my own (interested but inexpert) thinking about it – which followed from encountering claims that Hydrogen fuels make water vapor, a greenhouse gas (‘but clean energy is dirty and makes global warming worse’). Not only is water vapor produced from fossil fuel burning there are all those cooling towers and all that land irrigation (seems likely that last would be the largest anthropogenic source). The global warming impacts of Hydrogen use won’t be from the water vapor produced, it will be from the effects to atmospheric methane decomposition.
Without doing the studies it seemed likely to me that warming itself adds (induces) more rise in water vapor than anything else humans do – and makes an increase that persists. Glad (sort of) to know I wasn’t wrong.
In Re to Ken Fabian, 18 Aug 2025 at 10:18 PM
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-837886
Dear Ken,
Thank you for your post. I think that your summary shows that the recent „update“ on anthropogenic water vapour emissions
https://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/
may be indeed confusing, as I objected on 31 Jul 2025 at 9:21 PM ,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836721
As a clear information on this topic, I would rather recommend the older Real Climate post
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836721
As you can take therefrom, tropospheric water vapour “emissions” from cooling towers or irrigation have a negligible influence on atmospheric water vapour concentration, due to very short average residence time of water vapour in the troposphere.
What indeed matters with respect to anthropogenic contribution to greenhouse effect may be STRATOSPHERIC water vapour emissions:
“Only the stratosphere is dry enough and with a long enough residence time (a few years) for the small anthropogenic inputs to be important. In this case (and in this case only) those additions can be considered a forcing. Oxidation of anthropogenic methane (which is a major source of stratospheric water) and, conceviably, direct deposition of water from increases in aircraft in the lower stratosphere, can increase stratospheric water and since that gives a radiative forcing effect, they do appear on the forcings bar chart (under “H2O from CH4“). Some scientists have argued that changes to irrigation and other land use changes (which effect evaporation) are also direct forcings to water vapour amounts, but I think it’s cleaner to think of that as an indirect water vapour response to the change.“
You are right that hydrogen emissions might act as another, additional source of stratospheric water vapour, because hydrogen may oxidize in the stratosphere to water. I do not know, however, if this direct effect is more important than the possible indirect effect through an increase in the residence time of the stratospheric methane, due to competition between hydrogen and methane for the oxidizing hydroxyl radicals.
Anyway, it appears that possible contribution of hydrogen emissions to the greenhouse effect due to above mentioned interferences with atmospheric chemistry of Earth stratosphere may not be the worst disadvantage of the „hydrogen economy“. This may be rather the low volumetric energy density that makes hydrogen an inherently more expensive medium for energy storage and/or transport in comparison with other alternatives.
With respect to the “water vapour feedback” (an increase in the average absolute air humidity due to increased global mean surface temperature, GMST), I think that it pertains solely to the tropospheric water vapour. In this respect, I would like to make you aware that some of the “direct anthropogenic tropospheric water vapour emission”, like e.g. irrigation, may in fact DECREASE this feedback, due to their cooling effect on the GMST.
Oppositely, restricting the “direct natural tropospheric water vapour emission” (e.g., by wetland drying or landscape urbanization) may have an overall warming effect on the global climate, because the restriction of the latent heat flux and the GMST increase resulting therefrom do finally increase the global absolute air humidity and thus also the greenhouse effect of the water vapour comprised in the atmosphere:
https://iopscience.iop.org/article/10.1088/1748-9326/acdbe1
Greetings
Tomáš
Thank you Tomáš – lots of good information.
In Re to Ken Fabian, 19 Aug 2025 6:11 PM,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-837955
Hallo Ken,
Thank you very much for your kind feedback.
Actually, I have found out that in my post, I messed up the links.
The introduction should correctly read:
“.. the recent „update“ on anthropogenic water vapour emissions
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/
may be indeed confusing, as I objected on 31 Jul 2025 at 9:21 PM ,
https://www.realclimate.org/index.php/archives/2025/07/are-direct-water-vapor-emissions-endangering-anyone/#comment-836721
As a clear information on this topic, I would rather recommend the older Real Climate post
https://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/ ”
–
I apologize to you as well as to all other readers for the inconvenience caused by this mistake.
Greetings
Tomáš