Scientists find a control knob for climate feedbacks in the Southern Ocean. Two experts with years of research and publications: Dr. Zach Kaufman at Scripps Institute in San Diego, and Professor Richard Williams, University of Liverpool. The Southern Ocean stores most heat and almost half the carbon we add to the atmosphere. We would be cooked without it.
I’m Alex Smith. Let’s go down to that unknown frontier of climate change.
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HOW THE SOUTHERN OCEAN SAVED US… SO FAR
RICHARD WILLIAMS
When it comes to soaking up excess heat we add to the atmosphere, the Southern Ocean is doing the heavy lifting. Over decades, Professor Richard Williams investigated the role of oceans in climate change. With his PhD in Physical Oceanography, Williams is Professor Earth, Ocean and Ecological Sciences at the University of Liverpool.
Listen to or download this 28 minute Richard Williams interview in CD Quality or Lo-Fi
Professor Richard Williams led papers into “The role of the Southern Ocean in the global climate response to carbon emissions” and more recently “Asymmetries in the Southern Ocean contribution to global heat and carbon uptake”.
WHERE IS IT?
The location of the Southern Ocean still seems in doubt. Many public sources call this sea anything south of 60 degrees latitude. Another recent study on oceanography used 54 degrees south as the boundary. This new paper defines the Southern Ocean as something much smaller: ocean south of 30 degrees South.
Whether you define the Southern Ocean narrowly or more broadly, this is a relatively small share of the total world ocean. The Pacific alone is 8 times bigger. But, as the University of Liverpool press release says:
“Their findings, published in the journal Nature Climate Change, show that for the period from 1861 to 2005 the Southern Ocean contributed nearly twice as much to the global ocean uptake of heat compared to the global uptake of carbon.
Their analysis of state-of-the-art models of carbon and heat uptake across global oceans covering this period revealed large differences in uptake, with the Southern Ocean accounting for 83% of global ocean heat uptake and 43% of global ocean carbon uptake.”
SOUTHERN OCEAN FUTURE RESPONSE
Williams et al paper also warns:
“…the past is not a reliable indicator of the future”
...with the northern oceans becoming important for heat uptake while the Southern Ocean remains important for both heat and carbon uptake.”
“This finding challenges the widely held view of the unique Southern Ocean overturning circulation being the linchpin of global ocean warming, instead suggesting that its importance is currently exacerbated due to hemispheric biases in surface heating, and that its role in future warming will be reduced relative to that of the rest of the global ocean.”
Models assume that human-caused aerosols will decrease as this century progresses. For example switching from gas and oil to electric transportation may drastically reduce fossil fuel burning and all the aerosols that creates.
If aerosols decrease in the Northern Hemisphere, that will re-balance heat uptake between the Hemispheres, the authors say. Not considered: what if humans continue to burn fossil fuels right to end of century, and/or new sources of aerosols appear, like dust from droughts or constant forest fires (not to mention volcanoes). I think we should also try models where aerosols are only slightly reduced….
For this study, the authors selected the IPCC SSP2-4.5, scenario, calling it “middle of the road”. I think that is an optimistically low road. It would be interesting to run these projections using the worse outcome, the old RCP8.5, the path we are currently on.
Ric Williams’ web site is here.
Read more about this paper in the University of Liverpool press release “Study reveals historical mismatch in Southern Ocean contribution to heat and carbon uptake revealed”.
SEE ALSO: Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models Thomas L. Frölicher et al. January 15, 2015
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SOUTHERN OCEAN
SHAPING CLIMATE AND OUR FUTURE
ZACHARY KAUFMAN
Against all expectations and model predictions, and despite record global warming – the ocean at the south end of the world is cooling. Is the Southern Ocean acting like a brake on global warming? Do changes there re-arrange climate where you live, even on the other side of the world?
I’m trying to combat “North-ism” – where the majority of humans in the Northern hemisphere think climate is wholly determined there. We remain ignorant of new science about the Southern Ocean. What if our future is determined there, and not “here”?
Our guest Zachary Kaufman is a postdoctoral scholar affiliated with the Scripps Institute of Oceanography in San Diego. He specializes in Polar Ocean dynamics and publishes papers about both Poles. In March 2025, Kaufman led a paper investigating cooling in the Southern Ocean – and where climate models go wrong. He is Lead Author of the paper “The Impact of Underestimated Southern Ocean Freshening on Simulated Historical Sea Surface Temperature Trends”.
Listen to or download this 27 minute Zach Kaufman interview in CD Quality or Lo-Fi
A 2023 paper led by Sarah Kang said: “Recent global climate feedback [is] controlled by Southern Ocean cooling.” That is a huge statement. The Southern Ocean regulated climate feedback.
From the 2025 paper led by Z. Kaufman:
“From 1979 to 2015, anomalous Southern Ocean surface cooling and sea-ice expansion occurred despite global mean warming (Fan et al., 2014; Turner & Comiso, 2017). “ But in the last few years, Kaufman tells us, this Southern Ocean cooling has been reversed. The S. Ocean surface temperatures are slowly warming. We don’t know if that is part of a longer cycle, or whether this new warming is permanent or not.
IMPACTS OF ANOMALOUS SURFACE COOLING
In their introduction, Kaufman et al present a long list of previous explanations for Southern Ocean cooling. They find five theories, and chose one:
“Historical cooling may also be the consequence of an ongoing freshening trend in the Southern Ocean mixed layer, which enhances density stratification and inhibits upward vertical heat fluxes from below the pycnocline (De Lavergne et al., 2014; Kirkman & Bitz, 2011).”
The Kaufman et al paper says:
“This period of anomalous surface cooling [in the Southern Ocean] has global climate impacts, including
[*] increased Southern Ocean heat uptake (Lin et al., 2021),
[*] lower-tropospheric stability in the tropics (Dong et al., 2019), and
[*] increased low-cloud cover in the subtropics (Kang et al., 2023; Myers et al., 2023),
– which collectively reduce both the transient global warming rate and effective climate sensitivity (Andrews et al., 2018, 2022; Dong et al., 2022). “
SEA ICE AGAIN
Zach Kaufman has studied sea-ice decline at both Poles. A paper from April 2025 suggested Antarctic Sea ice decline was partly caused by a rhythm of surface temperature variations in the Pacific.
Antarctic sea ice crashed about 15 years ago. I think it hit another record low just last month. Arctic Sea for middle of December 2025 is at a record low for sure. I’m not sure we know why (as in proximate causes while the long-term cause we know).
BACK DOWN BELOW
It is dangerous to travel in the Southern Ocean. The storms and winds are legendary. That is another reason we are still just learning about the it. A new paper, December 3 2025 suggests ocean warming in the southern summer is regulated by these storms. Does world climate partly depend on winds and storms in the Southern Ocean, and is there any suggestion those might change in a warming world?
MODEL PROBLEMS
This cooling of the Southern Ocean while the rest of the world warms is counter-intuitive. In fact, the best coupled climate models did not predict that. after checks and calculation, Kaufman’s team finds adding previously uncounted precipitation and melt-water is enough to correct model predictions, at least matching observations so far.
ZACH KAUFMAN FURTHER REFERENCES
Kaufman sent along these papers for listeners who want to dig in deeply.
Kim, Hanjun, et al. “Subtropical clouds key to Southern Ocean teleconnections to the tropical Pacific.” Proceedings of the National Academy of Sciences 119.34 (2022): e2200514119. See Figure 5 for an excellent schematic of the Southern Ocean – Tropical connection.
Abram, Nerilie J., et al. “Emerging evidence of abrupt changes in the Antarctic environment.” Nature 644.8077 (2025): 621-633. An overview of recent Southern Ocean changes, including the recent reversal of the cooling trend and discussion of tipping points.
I WOULD ADD…
Does Southern Ocean Freshening Explain Recent Antarctic Sea Ice Trends? Z. Kaufman et al – The Ocean Sciences Meeting (OSM) 2024, held in New Orleans, LA, 18-23 February 2024.
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Listen to or download this show theme song: “Bottom of the World”
This show ends with the song “Down at the Bottom” (of the world). Lyrics by Alex Smith, AI music, Creative Commons license. I wrote that for the September kick-off show for the fall season of Radio Ecoshock. There we explored new science and new worries about Antarctica. This Southern Oceans show compliments that.
Coming up next week: our annual holiday music special. Listen for a whole hour of Radio Ecoshock climate music for those in the fire and flood zones, for ordinary people caught up in the climate whirlwind.
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