Ocean Evaporation Is Slowing—And the Wind May Be to Blame

Redacción HC
08/04/2025

For decades, climate models have predicted that warming oceans would lead to higher rates of evaporation, fueling a more intense global water cycle. But new research published in Geophysical Research Letters (February 2025) uncovers a surprising reversal: global ocean evaporation has been declining since 2008—despite continued ocean warming.

The key culprit? Wind stilling, a widespread weakening of surface wind speeds that’s quietly reshaping Earth’s hydrological engine.

Evaporation: The Ocean’s Breath

Evaporation from the ocean’s surface is the largest source of atmospheric moisture on the planet. It drives cloud formation, influences rainfall patterns, and supports agriculture and freshwater availability across continents. Traditionally, rising sea surface temperatures (SSTs) have been associated with increased evaporation. But this assumption may no longer hold.

A study led by Ning Ma and colleagues from the Chinese Academy of Sciences and Tsinghua University analyzed nearly three decades of satellite data (1988–2017) to measure changes in global ocean evaporation (Eₒ). Their findings reveal a distinct turning point around 2008, after which evaporation rates declined in nearly two-thirds of the world’s oceans.

A Closer Look at the Data

Methodology and Data Sources

The researchers synthesized four leading satellite products—OAFlux, Ifremer, HOAPS, and J-OFURO3—to calculate latent heat flux, a proxy for evaporation. These were calibrated using in-situ buoy data to ensure accuracy.

Using segmented regression analysis, the team pinpointed 2008 as a statistically significant breakpoint in the evaporation trend. They then decomposed the drivers of this trend into two key components:

• Humidity deficit: The difference in vapor pressure between ocean water and the overlying air.
• Surface wind speed: The air movement needed to transfer moisture into the atmosphere.

Their models revealed that before 2008, rising humidity deficits explained about 83% of increased evaporation. After 2008, however, a drop in wind speed was responsible for 62% of the decline, outpacing the effect of continued warming, which contributed only 38%.

The Calm After the Heat

Why Wind Stilling Matters

Surface wind is essential for evaporation—it "sweeps" water vapor off the surface and allows more to rise. Without wind, even warm oceans can't release moisture efficiently.

The study links this wind stilling phenomenon to changes in atmospheric circulation, possibly related to internal climate variability such as the North Atlantic Oscillation (NAO) and other large-scale wind patterns. Similar wind stilling has been documented on land (affecting pan evaporation), but this is the first study to confirm its large-scale presence over oceans.

“It’s like boiling water in a sealed room—heat builds up, but without airflow, steam doesn’t escape,” said co-author Yongqiang Zhang.

Regional Effects: Not All Oceans Are Equal

While the trend is global, its intensity varies by region:

• South Tropical Pacific: Experienced the strongest wind decline and thus evaporation slowdown.
• North Pacific and Atlantic: Saw some compensation from increased humidity, partially offsetting wind effects.

These regional differences have real consequences. Rainfall patterns, monsoons, and drought risks depend on the movement of ocean moisture. In some areas, weaker evaporation could reduce inland precipitation, impacting water supply and agriculture.

Rethinking Climate Assumptions

Implications for Climate Models and Policy

This study challenges one of the foundational assumptions in many climate models: that warming alone accelerates the water cycle. If wind speed acts as a limiter, then projections of future rainfall, runoff, and water availability may be overestimating hydrological intensification.

It also underscores the need to:

1. Incorporate wind variability into climate and hydrological models.
2. Expand post-2017 satellite monitoring to determine if the trend continues.
3. Investigate the physical causes of wind stilling, including shifts in global pressure systems and ocean–atmosphere interactions.

As lead author Ning Ma notes, “Climate isn’t just about temperature—it’s about motion, circulation, and feedbacks. Wind is a silent but powerful regulator.”

Consequences for Society and Ecosystems

Reduced ocean evaporation may have cascading effects:

• Water Scarcity: Lower moisture transport means less rain for continental interiors, especially in regions already facing droughts, such as the Amazon basin and southern Africa.
• Agriculture: Crops dependent on predictable rainfall patterns may suffer from altered moisture dynamics.
• Policy Relevance: Global water management and adaptation strategies must account for more than just temperature and CO₂.

“This could help explain why some regions are seeing less rainfall than expected under global warming,” said co-author Yuting Yang.

Conclusion: When the Wind Stops, So Does the Rain

This new study introduces a critical twist in the climate narrative: global warming does not automatically mean more evaporation. The atmosphere's ability to move moisture—powered largely by wind—plays a decisive role.

As we face growing challenges related to droughts, floods, and water security, understanding the full dynamics of the hydrological cycle is more urgent than ever.

Topics of interest

Climate