New research warns that even if humanity achieves net-negative emissions and cools the planet, the Southern Ocean might suddenly release its accumulated heat, restarting warming. This 'burp' could persist for at least a century. Scientists emphasize the need for rapid emission cuts to minimize such risks.
The Southern Ocean, which encircles Antarctica, has absorbed more than 90 percent of the excess heat humans have added to the atmosphere since the Industrial Revolution, along with a quarter of CO2 emissions. This vast body of water holds around 80 percent of the warmth taken up by all oceans, thanks to currents transporting warmer waters southward and upwelling that brings cold surface water to be heated.
A new modeling study, published on November 7, 2025, explores a scenario where atmospheric CO2 levels double pre-Industrial amounts by increasing 1 percent annually, then decline by 0.1 percent each year through negative emissions technologies. In this case, global temperatures initially fall as the atmosphere, land, and oceans cool. However, the Southern Ocean's surface grows colder and saltier from new sea ice formation—freezing seawater rejects salt, densifying the surface layer. This instability allows warmer deep waters to rise in a process called deep convection, releasing stored heat abruptly.
"At some point, the water column becomes unstable, and that’s when we have the deep convection event," explained Svenja Frey, an oceanography PhD student at Germany’s GEOMAR Helmholtz Centre for Ocean Research Kiel and coauthor of the paper.
The resulting heat 'burp'—as scientists termed it—could drive planetary warming rates similar to today's for at least a century, even under net-negative emissions. While removing CO2 still nets a temperature reduction overall, the findings highlight uncertainties in Earth's response to climate manipulation.
"There’s very large uncertainty in the Earth system response to net-negative emissions—we don’t understand that very well," said Kirsten Zickfeld, a climate scientist at Simon Fraser University who was not involved in the study. "We may well encounter surprises along the way, as this paper shows."
The Southern Ocean's clearer skies, lacking the aerosol pollution that cools the Northern Hemisphere by reflecting sunlight, make it particularly effective at heat storage. Ric Williams, an ocean and climate scientist at the University of Liverpool not involved in the research, noted, "Doing negative emissions and reducing our carbon load in the atmosphere is a good thing. I would just add that, rather than do negative emissions, it’s better not to do the positive emissions in the first place."
This model is not a prediction but a step toward understanding ocean dynamics in cooling scenarios. It underscores the urgency of slashing emissions now to limit the heat stored in the seas.