A recent study published in Geophysical Research Letters, has turned up a surprising result: global ocean evaporation, a cornerstone of the hydrological cycle, has been declining since the late 2000s despite steadily warming sea surfaces. This runs counter to the widely held view that a warmer climate should boost evaporation rates. For those tracking discrepancies in climate science, this is worth a closer look.
The researchers analyzed satellite data spanning 1988 to 2017, drawing from four independent products: J-OFURO3, SeaFlux, HOAPS, and IFREMER. Their findings show that global ocean evaporation—which supplies about 85% of the atmosphere’s water vapor—rose sharply over the first two decades of the period, peaking around 2008. Then, the trend flipped. From 2008 to 2017, the global average dipped slightly, with two-thirds of the ocean experiencing reduced evaporation. This was validated, where possible, against buoy observations from the Global Tropical Moored Buoy Array, though coverage is sparse beyond the tropics.
Abstract
Ocean evaporation (Eo) is the major source of atmospheric water vapor and precipitation. While it is widely recognized that Eo may increase in a warming climate, recent studies have reported a diminished increase in the global water vapor since ∼2000s, raising doubts about recent changes in Eo. Using satellite observations, here we show that while global Eo strongly increased from 1988 to 2017, the upward trend reversed in the late 2000s. Since then, two-thirds of the ocean have experienced weakened evaporation, leading to a slight decreasing trend in global-averaged Eo during 2008–2017. This suggests that even with saturated surface, a warmer climate does not always result in increased evaporation. The reversal in Eo trend is primarily attributed to wind stilling, which is likely tied to the Northern Oscillation Index shifting from positive to negative phases. These findings offer crucial insights into diverse responses of global hydrological cycle to climate change.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL114256
What’s driving this? The study points to “wind stilling”—a measurable drop in near-surface wind speeds, particularly pronounced in the Southern Hemisphere. They link this to the Northern Oscillation Index (NOI), a measure of pressure differences between the North Pacific High and near Darwin, Australia, shifting from positive to negative phases after 2008. This phase change aligns with weakened trade winds and a broader slowdown in atmospheric circulation, outweighing the evaporation boost expected from rising sea surface temperatures (SSTs).
This challenges a core assumption in climate science: that evaporation scales predictably with temperature via the Clausius-Clapeyron relationship, where warmer air holds more vapor and thus pulls more water from the surface. The study’s data shows SSTs climbing as expected, increasing the air-sea humidity deficit—a key driver of evaporation. Yet wind speed’s decline overpowered that effect, cutting evaporation anyway. The authors quantify this using a multiple regression model, finding wind speed accounted for 62% of the post-2008 drop, compared to 38% from humidity changes.
The ramifications are significant. First, a weaker evaporation signal could reduce the moisture feeding precipitation, especially for land regions relying on ocean-derived vapor. The study notes spatial variation—declines were strongest in the southern tropical Pacific, Indian Ocean, and extratropical Atlantic—suggesting uneven impacts on rainfall patterns. Second, it could alter ocean salinity trends. Evaporation typically concentrates salt at the surface, but a slowdown might ease that process, particularly in subtropical zones where it dominates over precipitation. This could subtly influence density-driven ocean currents, though the study doesn’t claim dramatic shifts like an Atlantic Meridional Overturning Circulation disruption.
For climate modeling, this is a wrinkle. Most global circulation models (GCMs) project an intensified hydrological cycle under warming—more evaporation, more rain, more extremes. But if wind speed can override temperature effects, those projections might overshoot reality. The authors frame this as a possible natural cycle tied to decadal oscillations like the NOI or Pacific Decadal Oscillation, not a permanent climate change signature. Still, they leave the door open: if human-driven warming (e.g., polar amplification) is quietly slowing winds, this could signal a longer-term shift. With data ending in 2017, we’re stuck waiting for updates to settle that question.
Uncertainties linger. The satellite datasets aren’t flawless—HOAPS, for instance, shows a steeper drop, possibly due to quirks in its microwave sensor platforms (SSMI/SSMIS), while the others temper that signal by blending multiple sources. Buoy validation helps, but it’s spotty outside tropical zones, leaving high-latitude trends less certain. The study also sidesteps intra-annual shifts and secondary drivers like radiation or upwelling, focusing narrowly on wind and humidity. Future work, they suggest, could refine this with better measurements—think next-gen satellites or ocean drones.
It’s another case where observations don’t match the script. The “warming equals wetter” narrative takes a hit when a natural factor like wind can call the shots. It’s not a knockout blow to climate orthodoxy—evaporation rose for decades before 2008, tracking warming—but it exposes gaps in the models and the risk of over-relying on simplified physics. Is this a strong indicator that atmospheric dynamics are more in charge than CO2-driven forecasts admit? The study doesn’t preach; it just lays out the numbers. That’s plenty of fuel for discussion.
[Link to study: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL114256]
H/T Dr. Judith Curry
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An evaporative cooler has zero cooling effect if the fan isn’t turned on.
what about a Coolgardie safe?
They still require air movement. Many cockies hang them on the front of their vehicle. 🙂
Sounds like good news for Hurricane potential. Less evaporation equals less moisture available for storm formation and strengthening
The Hurricanes haven’t been as strong as forecast for some time.
No they don’t.
You are talking about canvas water-bags cooled by evaporation caused by capillary action that does not work if they are chucked on the cabin floor.
A Coolgardie safe cools the same way (by latent heat loss) but cooling results from the warmer drier air going past the canvas or sugar-bag draped over the safe, dipping into a water trough.
You end up with cool water, or a cooler safe but not colder water or a refrigerator. Neither work so well under conditions of high humidity and temperature. .
Yep, you are right Bill. My bad 🙁
A song that mentions the ‘Coolgardie”
“Put A Light In Every Country Window”
https://www.youtube.com/watch?v=_Ku6vwczeQU
The old Coolgardie and the red hot wood stove
They each have seen their days at last
For now the ice and fire that is coming on the wire
Has made them all relics of the past
Of all places to run into a Coolgardie, Tecopa Hot Springs, California. A lady there had one as a back-yard decoration.
If you are trying to suggest that evaporation cannot take place in the absence of wind, I’ll suggest that you are wrong. If you are trying to suggest that evaporation does not lower the temperature of the evaporating liquid without wind, I’ll suggest that you are wrong there, as well.
Maybe you could quote the words in the article which prompted your comment. It’s a bit confusing as it stands.
What I meant to imply is that there is a lot less evaporative cooling when there is no wind.
Just didn’t say it very well, hey !
Haven’t seen much attention to Langmuir circulation which increases with wind producing foamy bubbles where currents collide. If you can avoid seasickness heavy waves are fascinating and not only increase the surface area but must be rapidly changing the surface water. It was covered some after the recent Gulf of Mexico big spill, not a very new subject. Us biologists maybe know more about them. This is another paper stuck in this century so you have go back to see if references are similar which takes lots of time. I think we need to get these ‘experts’ back to making ship’s logs and watching the birds and flying fish ride wave surfaces.
Schmidt, W. 1936. Cause of ‘Oil Patches’ on water. Nature. 137:777.
Barstow, S. F. 1983. The ecology of Langmuir circulation: A review. Mar. Envir. Res. 9:213-236.
Even something as simple as evaporation of water can yield surprising findings upon further inspection.
https://news.mit.edu/2023/surprising-finding-light-makes-water-evaporate-without-heat-1031
Light goes into a clear ocean to a couple of hundred feet. Then what happens?
It is called light. Is it not energy?
Yes it is energy, but the absorption is very weak, so is well dispersed and mostly well below the surface.
“The absorption is very weak”. Yes, but at ocean depths absorption is complete, that’s why it’s completely dark down there. (This is Beers law, absorption coefficient, optical path, concentration.) Virtually all of that visible light energy is transformed into thermal energy. (First law of thermodynamics).
So if a single photon is absorbed by a single water molecule, there has been a transfer of heat. (2nd law of thermodynamics)
The physics is identical across the EM spectrum.
Absorption of (light) enegy is the definition of radiative heat transfer. How can MIT claim the experiment demonstrates evaporation without heat?
Evaporation occurs at constant temperature. These particular MIT students are redefining some thermo terminology to get their 15 minutes of fame….
to get their 15 minutes of fame… by fooling mother nature?
“When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling”
https://en.m.wikipedia.org/wiki/Evaporation
There is no free lunch in thermodynamics.
Like the UN/IPCC changed the definition of “climate” to only mean around 30 years of weather instead of the thousands to millions of years of weather the the word was taught to mean to billions of people and that is very seldom mentioned..
Yes it is electromagnetic energy. It’s not heat that produces temperature until it is absorbed by something. Otherwise outer space between here and the Sun would be quite hot…
Easily explained by EM fields and waves math.
When I was in graduate school I helped a group measuring gas diffusion for photosynthesis and respiration. I seem to recall that the coefficients of diffusion are variable and would somewhat be positively correlated with wind speed. The ocean surface is full of surfactants whose concentrations vary greatly. For some time I have been interested in vapor pressures across ocean surface tensions where fish and other organisms operate and gather that it is still somewhat a mystery. One of the earliest studies was Woodcock, A. H. 1941. Surface cooling and streaming in shallow and fresh and salt waters. J. Mar. Res. 4(2):153-160. I haven’t payed attention to heat transfer but these are the more recent ones that I’ve checked and would be interested in others. Rahlff J, Stolle C, Giebel H-A, Ribas-Ribas M, Damgaard LR, Wurl O (2019) Oxygen profiles across the sea-surface microlayer—Effects of diffusion and biological activity. Front Mar Sci 6(11):1-14 https://doi.org/10.3389/fmars.2019.0001
Soloviev A, Lukas R (2014, 2nd Ed). The Near-Surface Layer of the Ocean Structure, Dynamics and Applications. Springer. 552pp. Chapter 2
Doesn’t heating of the surface create wind? Just another way for heat to move from where it is to where it is not? And the greater the temperature difference; the strong the forces to bring those differences into equilibrium…?
Heating and cooling cycles cause wind.
But cool things warm up faster than warm things given the same increase in energy flux, so as the world warms, the temperature difference shrinks.
It shrinks from equator to polls, it shrinks from day to night, it shrinks from winter to summer, it shrinks from low altitudes to high altitudes. Everywhere the temperature difference from highs to lows shrinks.
A warmer world is a calmer world once you subtract the climate hysteria.
Not all that much, some times. It does create convection, but if the general airmass has little wind, convection is just some slowly rising (and sinking) air.
If the airmass does have moderate wind, the morning convection helps mix the ground level air chilled by radiational cooling back into to the airmass, and that lets upper level winds reach the ground.
Voodoo science; borders on superstitious.
You cannot have evaporation without convection. Otherwise, there is 100% humidity at the water surface, and hey presto, there is no evaporation. (Not quite true – you can have mist and fog, which is negative evaporation!)
Cheers,
Dr Bill Johnston,
http://www.bomwatch.com.au
“where warmer air holds more vapor and thus pulls more water from the surface.”
Air does not “pull” water from the surface. That sounds like the sort of thing a “climate scientist” would say.
On a more serious note, reduced water vapour in the air results in hotter maxima, and colder minima – as found in arid deserts (or the Moon’s surface).
Nothing to do with any mythical “greenhouse effect”, just basic physics, as John Tyndall realised over a century ago.
Much ado about not much at all.
“Climate Scientist” (n): Propaganda pushing activist who pretends to be an *actual* scientist.
Let’s see: wind speed declines — less evaporation, check, ocean surface covered with life and associated surfactants — less evaporation, check. Anything else? Well, arguments to the effect that evaporation is proportional to saturated vapor pressure at the surface minus actual vapor pressure at, say, 4m above neglects that energy must be supplied to the surface layer because evaporation requires energy. Lots of ways to model this wrong.
“Lots of ways to model this wrong.”
True story.
As I have pointed out before, total water vapor over my site exhibited zero trend from 1990 to 2020. I published that in Bulletin of the American Meteorological Society (BAMS), but only after the 3 reviewers wanted more information. My record reached 35 years on 4 Feb 2025, and the trend remains flat. However, the NASA Cimel instrument at my AERONET site showed a distinct increase in total water vapor during the past two summers. The most obvious explanation is the historic eruption of the underwater Hunga Tonga volcano. Forrest M. Mims III
Your data pretty much proves the “positive feedback from increased water vapor” to be bogus.
BTW, I enjoyed reading your columns in Popular Electronics.
“The Science is settled!!!”
No, the propaganda is settled. Science is just a method … and is never settled.
There is a name for “settled science” – engineering.
I’m a firm believer in defining science as man’s continuing process of refining the model that describes nature. FWIW, I did take a couple of courses in the history of science taught by Kuhn’s Protégé, John Heilbron.
I also thought the science was settled and the models are based on known physics
“For climate modeling, this is a wrinkle” – OOPS!!!
The relationship only applies to the oceans where the available surface water is unlimited. The atmosphere reaches cyclic equilibrium once the surface temperature reaches 30C. Temperature rise above that is fleeting while the amosphere equilibrates with the surface.
The atmospheric moisture over oceans has maintained an increasing trend to 2023 of 0.4mm/decade as the NH oceans warm.
image-104.png
That is a significant upward trend given that the global average is just 26mm.
Summer advection from ocean to land in the NH is slowing down so it is expected that ocean evaporation would be reducing. More of the NH ocean surface is reaching the 30C equilibrium temperature because there is less heat advection to the land from the oceans.
And all those coastal wind turbines robbing the wind energy further reduces the coastal advection
> since the late 2000s
By my reckoning 2025 is still in the early 2000’s 🙂
Atmospheric dynamics always change in a way that neutralises potential disruption to the system.
convection changes to cancel out all threats including changes in the radiative properties of atmospheric gases.
As I’ve been saying for years.
Convective overturning of atmospheric
mass both causes the so called greenhouse effect and keeps it stable.
GHGs are not the control knob, convection is.
Yup…
Le Chatelier’s Principle
LOL, they labeled 2008 a “turning point”.
Silly researchers. They’re supposed to be looking for tipping points.
How does one measure evaporation over an entire ocean? Answer, you can’t.
From the article: “recent study published in Geophysical Research Letters, has turned up a surprising result: global ocean evaporation, a cornerstone of the hydrological cycle, has been declining since the late 2000s despite steadily warming sea surfaces.”
Are the oceans steadily warming? This implies that every stretch of water is steadily warming, yet it wasn’t long ago that it was discovered that some ocean areas in the Atlantic ocean were cooler than normal, so this particular area is not steadily warming.
The world’s oceans are not like a bathtub, as is implied, where the entire volume of water is slowly warmed. No, the oceans, just like the land, have warm areas and cool areas.
This “steadily warming” meme is inaccurate and is climate alarmist propaganda.
It must be nearly 2 years ago that I blogged that just because a warmer atmosphere could take up more water, that did not mean that it would take up more water.
There remain some major effects in the whole global warming narrative that are not well explained by current thinking, current models or current propaganda about settled science and who owns it. At times, one can gain an impression that a key part of the climate jigsaw is missing. An example might be that the interchange of energy with the vast oceans might be influenced by changes in abundance or depth of marine organisms affecting optical properties. I am not proposing exactly that because of inadequate measurement, but I mention it to illustrate scale and difficulty of detection of small changes that are important because of large scale. Uncertainty thrives. Geological people used to long time scales and large volumes might understand such concepts better than those who sit by computer model screens. Geoff S
Like anything else in the natural world, wind speeds and wind distribution patterns cycle up and down. Duh!
It is indisputable that the physics dictate that warmer water emits more water vapor than cooler water. Due to the vapor pressure factor. How much of that emitted water vapor ends up in the atmosphere (on a mass basis) depends upon a number of things, not just wind speeds. The relative humidity of the atmosphere has an effect, including a consideration of the saturation point. Clouds and sunshine have an effect. The temperature of the air has an effect, though over time the temperature of the air is determined by both the solar energy absorbed and the heat emitted or absorbed by the oceans.
It is also indisputable that over long timeframes, a warmer world, which means also warmer oceans, is a higher relative humidity or wetter world.
Thus the warmunist’s repeated blaming of drought on global warming is ridiculous on its face.
The warmunist’s blaming of LOTS of things on global warming are all ridiculous on their faces.
The people who are surprised by this “unexpected” result clearly lack critical thinking skills and do not understand cause and effect. If you begin with the datum that sea surface temperatures are rising, one of the possible causes of that would be precisely “reduced evaporation from the surface.” Less energy leaves the surface by evaporation, and therefore surface temperature increases. It is basic physics; in fact, physics doesn’t get any more basic than that.
For example, there are two identical pots of water on a stove, except one is covered and the other is uncovered. Which will heat up faster? The pot with the lid, of course. Reducing the escape of hot vapors leads to a smaller amount of energy leaving the system.
Since this is a simple mechanism that could explain rising sea surface temperatures, it is a hypothesis that should have been investigated in the first place, not an “unexpected result.” Does anyone anymore know how to do science? No, because nobody knows how to think like a philosopher.
My personal experience: I live in the Southern USA along the I-20 line east of the Mississippi River. At the beginning of each summer, I wash off the accumulated dirt/pollen from my concrete screened in porch on the west side of my house always in the morning. The concrete is cooler than the air temperature and the water that puddles in the low places remains for long periods of time. However, if I add a box fan on high RPM, the water evaporates faster with that wind from the fan than the still air without it. The porch is always shady and the sun does not reach it until the afternoon. But the temperature does rise with increased daylight hours.
Should I apply for a government grant to study this phenomenon?
This study is a study of instrumentation readings versus computer generated speculation at best.
It states “This was validated, where possible, against buoy observations from the Global Tropical Moored Buoy Array, though coverage is sparse beyond the tropics.”
“….where possible……coverage is sparse….” are the dead giveaways.
Less wind results in less evaporation which results in higher ocean temp which results in more outward radiation of heat from the ocean at night. Heat ultimately dissipates and spreads out – never accumulates……. very complex system that still has unknowns means more difficulty explaining how the climate cools and heats over longer time periods. How about that Younger-Dryas period?
But the science is settled! So lets spend more trillions of dollars on the models.
So the oceans are suffering from a lack of “wind chill”? 😎
It’s another case where observations don’t match the script.
Too easy. Just slip in another proxy for evaporation and bobsyeruncle with the hockey stick script. Democrat sweat should fit nicely.