From Watts Up With That?

Essay by Eric Worrall

According to a recent study, climate models overestimate Southern Ocean surface heating, because they underestimate the impact of storms.

NEWS RELEASE 16-DEC-2025

Storms in the Southern Ocean mitigates global warming

Peer-Reviewed Publication
UNIVERSITY OF GOTHENBURG

Intense storms that sweep over the Southern Ocean enable the ocean to absorb more heat from the atmosphere. New research from the University of Gothenburg shows that today’s climate models underestimate how storms mix the ocean and thereby give less reliable future projections of our climate.

The Southern Ocean is a vast expanse of ocean encircling the Antarctic continent, regulating Earth’s climate by moving heat, carbon, and nutrients out in the world’s oceans.

It provides a critical climate service by absorbing over 75 per cent of the excess heat generated by humans globally. The Southern Ocean’s capacity to reduce climate warming depends on how efficiently it can absorb heat from our atmosphere.

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“Our research shows that summers with stronger storm activity generate lower surface temperatures across the Southern Ocean. Hence, a stormy ocean can absorb more heat from the atmosphere, then in calm weather,” says Marcel du Plessis, Researcher in oceanography at the University of Gothenburg and main author of the study.

How much heat the ocean absorbs from the atmosphere influences everything from how high temperatures will be on land, to the extent of sea ice and the severity of marine heatwaves.

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Current climate models, which underpin the climate projections used to guide policy, tend to underestimate the strength of Southern Ocean storms and thereby simulate an overly warm ocean.

“That is why our findings are important, because a better representation of storm processes is essential for more accurate future climate projections,” says Marcel du Plessis. 

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It’s in the Antarctic summer that storms have their strongest impact on ocean heat uptake. In winter, completely different processes take place. This will be the next challenge for researchers to observe and understand.

Media Contact

Olof Lönnehed
University of Gothenburg
olof.lonnehed@science.gu.se
Office: +46 766-186970

Expert Contact

Marcel du Plessis
University of Gothenburg
marcel.du.plessis@gu.se
Cell: +46 72 900 8118Read more: https://www.eurekalert.org/news-releases/1109536

The abstract of the study;

Published: 03 December 2025

Southern Ocean summer warming is regulated by storm-driven mixing

• Marcel D. du Plessis, 
• Sarah-Anne Nicholson, 
• Isabelle Giddy, 
• Pedro M. S. Monteiro, 
• Channing J. Prend& 
• Sebastiaan Swart 

Nature Geoscience (2025)Cite this article

Abstract

The Southern Ocean absorbs most of the excess heat resulting from climate change. However, climate projections show a persistent warm summer bias in its sea surface temperatures, indicating a limited understanding of the air–sea heat exchange mechanisms governing this region. Here we examine the impact of storms on the interannual variability of Southern Ocean surface temperatures during summer using in situ observations from underwater and surface robotic vehicles, climate reanalyses and satellite data. We show that synoptic-scale storms regulate summer sea surface temperatures through alteration of the effective heat capacity of the mixed layer and the entrainment of colder water from below. Storms reduce the summer ocean heat gain by limiting solar radiation reaching the surface. This effect is partially offset by a reduction in heat loss due to turbulent air–sea exchange. We also find that interannual variations in sea surface temperature during summer in the Southern Ocean are driven by changes in storm-mean wind speeds, which are linked to the Southern Annular Mode. Our results demonstrate a causal link between storm forcing and sea surface temperature variability, which is critical for reducing warming biases in climate models and improving future climate projections.

Read more: https://www.nature.com/articles/s41561-025-01857-3

From the study;

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During the third period (days 23 to 47), a series of intense storms deepened the mixed layer to about 100 m. This, along with a reduction of the mean net heat flux to 131 W m⁻², decreased the SST warming rate to 0.025 °C d⁻¹. The drop in heat flux was primarily due to the reduction in incoming top-of-atmosphere shortwave radiation (Fig. 2f). That said, with the positive net heat flux still large, the SST continued to increase until reaching the seasonal maximum (T_max = 2.28 °C). After this, the SST remained comparatively stable at −0.002 °C d⁻¹ as the net heat flux reduced to 88 W m⁻², again due to a drop in incoming shortwave radiation (Fig. 2f). This slightly negative SST tendency—despite the positive heat flux—can be explained by a multi-day entrainment-driven cooling associated with deep turbulent mixing, starting on day 47 (Fig. 2e and Extended Data Fig. 3). Thus, in addition to regulating MLD and the mixed-layer’s heat capacity, intense storms can reduce SST through wind-driven entrainment of cooler subsurface water. This is seen during two other notable SST cooling events in response to mixing below the MLD, on days 5 and 24 (Fig. 2a,c). Cumulatively, all three entrainment events reduced the SST by about 1 °C over the summer (Fig. 2a), with the two strongest events cooling the SST by 0.4 °C each (days 24 to 27 and days 47 to 52). These large SST changes, caused by individual storms, highlight the rectified effect of storm-driven entrainment on the seasonal-scale warming during summer.

…Read more: Same link as above

Interesting they forgot to mention the part about storms limiting solar radiation reaching the surface in the press release.

Another part they left out is how much this underestimated deep mixing is likely to retard global warming, thanks to the enormous thermal capacity of the oceans. Even if the model interpretation that most global warming is being absorbed by the ocean is correct, it would likely take thousands of years to nudge deep ocean temperature by a single degree. The ocean depths are just above freezing, 12,000 years of Holocene interglacial global warming has barely nudged the dial.

Given the uptick in storms when summer insolation heats the sea, storms which act to reduce sea surface temperature, it seems likely stronger than expected summer storms are yet another unaccounted-for negative feedback which works against climate alarmist fantasies of runaway global warming.