New research shows unexpected drop in ocean evaporation due to rising sea temperatures – Wattwat?

A recent study Geophysical Research Lettera surprising result: global ocean evaporation has been the cornerstone of the hydrological cycle since the late 2000s, despite steady warming of the sea surface. This is contrary to the widely believed view that warm climates should increase evaporation rates. For those who track differences in climate science, this deserves equal treatment.

The researchers analyzed satellite data from 1988 to 2017 and drew from four independent products: J-ofuro3, Seaflux, Hoaps and Ifremer. Their findings show that global ocean evaporation (about 85% of atmospheric water vapor) emanates dramatically during the first two decades of the period, peaking around 2008. Then, the trend changed. From 2008 to 2017, the global average dropped slightly, with two-thirds of ocean evaporation decreasing. Where possible, this is a validation of buoy observations for global tropical moored buoy arrays, although the coverage is sparse in the tropical area.

Abstract

Ocean evaporation (e_o) is the main source of atmospheric water vapor and precipitation. Although widely recognized e_o Probably increasing in warmer climates, recent research reports that the increase in global water vapor has raised doubts about recent changes since the 2000s e_o. Using satellite observations, we show here that although global e_o From 1988 to 2017, the upward trend increased significantly in the late 2000s. Since then, two-thirds of the ocean evaporation trend has weakened, resulting in a slight decline in the global average trend e_o During the period 2008-2017. This suggests that even on saturated surfaces, warm climates do not always lead to increased evaporation. reverse e_o The trend is mainly attributed to the wind static, which is likely to be related to the northern oscillation index transitioning from positive to negative phase. These findings provide important insights into the diverse responses of global hydrological cycles to climate change.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL114256

What driving is it? Research points out that “wind is still” – a measurable drop in near-surface wind speed, especially in the southern hemisphere pronunciation. They linked it to the Northern Oscillation Index (NOI), which measures of pressure differences in the North Pacific Highlands and near Darwin, Australia were measured from positive to negative stages after 2008. This stage of change is consistent with weaker trade winds and larger decelerations atmospheric circulation, exceeding the expected evaporation growth of sea surface temperature rise (SST).

This challenges the core assumption in climate science: Through the Claus-Claperon relationship, the evaporation scale predicts that at this temperature, the warm air can hold more vapors, thereby absorbing more from the surface water. Data from the study show that SST climbing is expected, increasing air humidity deficiency, which is the main driving force for evaporation. However, the decrease in wind speed overwhelms this effect, reducing evaporation anyway. The authors quantified this using a multiple regression model and found that wind speed accounts for 62% of the decline after 2008, while humidity changes were 38%.

Analysis is important. First, weaker evaporation signals can reduce water feeding precipitation, especially for land areas that rely on ocean-derived vapors. The study notes that spatial variation (strongest in the tropical Pacific, Indian Ocean and the southern tropical Pacific that induced the Atlantic Ocean) has uneven effects on rainfall patterns. Second, it may change the trend of ocean salinity. Evaporation usually concentrates salt on the surface But slowing may alleviate the process, especially precipitation that dominates the subtropical region. This may subtly affect density-driven currents, although the study does not claim to be as dramatic as the cycle interruption of Atlantic meridian capsulation. The transformation.

For climate modeling, this is wrinkles. Most Global Cycle Models (GCMs) project enhanced hydrological cycles under warming – more evaporation, more rain, more extremes. However, if wind speeds can exceed the impact of temperature, these predictions may exceed reality. The authors view it as a natural cycle that may be associated with aging oscillations such as NOI or Pacific Decadal oscillations, rather than permanent climate change characteristics. Nevertheless, they still open the door: If human-driven warming (e.g., polar amplification) quietly slows down the wind, this could mark long-term change. With the end of the 2017 data, we have been waiting for an update to resolve this issue.

Uncertainty continues. The satellite dataset is not flawless – HOAP, for example, shows a steep drop, which may be due to quirks in its microwave sensor platform (SSMI/SSMIS), while others signal by mixing multiple sources. Verification of buoys is helpful, but occupies spots outside the tropical regions, while high latitude trends are less certain. The study also avoids shifts and secondary drivers within the year, such as radiation or upflow, focusing narrowly on wind and humidity. They believe that future work can be refined with better measurement methods – considering the next generation of satellites or ocean drones.

This is another case where you observe a mismatch script. When natural factors like Wind can hit the camera, the “warming equals wet” narrative will take a hit. This is not a knockout blow to climate orthodoxy – evaporation has grown for decades before 2008, but it reveals gaps in the model and risks over-reliance on simplifying physics. Is there a strong indicator that atmospheric dynamics are more responsible than CO2-driven predictions? The study did not preach; it simply listed the numbers. This is a lot of fuel discussed.

[Link to study: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL114256]

Dr. H/T Judith Curry

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