New climate-model experiments show the Southern Ocean — which has absorbed more than 90% of excess heat and roughly 25% of emitted CO2 — could abruptly release stored warmth in a so-called 'burp.' As CO2 is removed and the surface cools and becomes saltier from new sea ice, deep convection can bring warm subsurface water to the surface and into the atmosphere. The modeled warming pulse could last at least a century and produce rates of warming similar to today, though removing CO2 still cools the planet overall.
The Southern Ocean's 'Burp': How Stored Heat Could Rewarm the Planet
New climate-model experiments show the Southern Ocean — which has absorbed more than 90% of excess heat and roughly 25% of emitted CO2 — could abruptly release stored warmth in a so-called 'burp.' As CO2 is removed and the surface cools and becomes saltier from new sea ice, deep convection can bring warm subsurface water to the surface and into the atmosphere. The modeled warming pulse could last at least a century and produce rates of warming similar to today, though removing CO2 still cools the planet overall.
18:58, 07.11.2025Environment
The Southern Ocean's 'Burp': How Stored Heat Could Rewarm the Planet
Think of a forgotten cup of coffee: the kettle heats the water, but if the cup sits, its warmth slowly leaks into the room until it cools. On a planetary scale, the Southern Ocean — the vast sea circling Antarctica — has been acting like that cup, absorbing more than 90% of the excess heat added to Earth's climate since the Industrial Revolution and taking up roughly a quarter of our CO2 emissions.
New climate-model experiments suggest that, under one plausible scenario, that stored heat could be released abruptly in what researchers describe as a 'burp.' In the simulations, atmospheric CO2 rises by about 1% per year until roughly double preindustrial levels, then net-negative removal reduces CO2 by about 0.1% per year. As the atmosphere and surface ocean cool, increased sea-ice formation ejects salt into the surface layer, making it colder and denser while relatively warm water remains at depth. That combination can destabilize the water column and trigger deep convection that brings subsurface heat to the surface and back into the atmosphere.
The modeled thermal pulse can produce a rate of warming comparable to today's human-driven trend and may persist for at least a century, even though net-negative emissions in the scenario still lower global temperatures overall. This outcome is not certain — it depends on model choices and assumptions — but it highlights a potentially important and underappreciated risk when planning large-scale CO2 removal.
Svenja Frey, a PhD student at GEOMAR Helmholtz Centre for Ocean Research Kiel and co-author of the study, said: 'The key question is how the ocean reacts to net-negative scenarios and a net global cooling effect.'
Several factors make the Southern Ocean especially effective at storing heat: strong upwelling brings cold deep water to the surface where it can absorb heat; Antarctic currents transport relatively warm water southward; and the Southern Hemisphere has experienced less aerosol-driven cooling than the north, leaving its skies relatively pristine and enabling greater heat uptake. The study estimates the Southern Ocean contains roughly 80% of the heat absorbed by the world's oceans.
Independent experts, including Ric Williams (University of Liverpool) and Kirsten Zickfeld (Simon Fraser University), stress large uncertainties in how the Earth system would respond to net-negative emissions and caution that surprises are possible. They also emphasize the policy takeaway: the faster we reduce greenhouse-gas emissions now, the smaller the negative-emissions effort required later and the lower the risk of unintended side effects like an oceanic 'burp.'
Bottom line: Removing CO2 from the atmosphere remains beneficial and reduces global temperatures in the modeled scenario, but the ocean's stored heat could temporarily counteract cooling for decades to a century. Avoiding emissions in the first place remains the most reliable way to limit long-term risks.