Climate: An Invisible Threat Lurks Beneath the Southern Ocean, Potentially Lasting Over a Century

For two centuries, the Southern Ocean has acted as an immense reservoir of heat, cushioning the effects of global warming. Although this role as a climate buffer has helped slow the increase in global temperatures, it could soon become a factor of major instability. A team of researchers from the GEOMAR Helmholtz Center for Ocean Research in Germany is warning of a potentially irreversible phenomenon: the sudden release, on the surface, of heat accumulated in the depths of the ocean around Antarctica.

This hypothesis, resulting from climate modeling published in October 2025 in the journal AGU Advances, shows that even after centuries of efforts to cool the planet, this “thermal runaway” could restart global warming for more than a hundred years. A perspective that calls into question the long-term stability of current solutions against climate change.

The Southern Ocean, a silent but fragile thermal buffer

The Southern Ocean plays a crucial role in global climate regulation. Surrounding Antarctica, it absorbs around 80% of the excess heat accumulated by the oceans since the start of the industrial era. While only representing 15% of their surface area. It thus constitutes the main shock absorber of the effects of global warming. It captures both heat and around a quarter of global CO₂ emissions.

This storage capacity is explained by two essential mechanisms. On the one hand, deep ocean currents carry warm waters from the tropics south. On the other hand, upwelling — a phenomenon by which cold water rises to the surface — exposes the water to the atmosphere, allowing heat exchanges. In this dynamic system, the trapped heat eventually sinks into the deep layers of the ocean.

But this storage is not infinite. “ The ocean system operates with great inertia », Specifies Svenja Frey, doctoral student at the GEOMAR Helmholtz Center for Ocean Research in Kiel, in a press release. This inertia means that the effects accumulated over centuries can suddenly come to the surface.

This return would be triggered not by a continued increase in emissions, but paradoxically in a context of global cooling. When the ocean surface cools and sea ice reforms, it releases salt into the surrounding water, making the surface layer denser. This density imbalance could cause deep convection, bringing heat-laden waters to the surface. This mechanism makes the Southern Ocean a delayed thermal bomb. A silent but active bomb, capable of upsetting the balance of the global climate.

Scientific modeling of a delayed climatic phenomenon

The study is based on climate modeling developed by the GEOMAR Helmholtz Center team. This forward-looking scenario explores what could happen if humanity reached net negative emissions. That is, if it managed to remove more CO₂ from the atmosphere than it emits. (A utopia, we admit…)

The model first simulates a continued increase in the concentration of CO₂ in the atmosphere, at a rate of 1% per year, until it doubles compared to pre-industrial levels. Then, negative emissions technologies — such as direct carbon capture — would allow an annual reduction of 0.1% in this concentration. This phase of decarbonization gradually leads to a cooling of the atmosphere, oceans and soils.

However, around the year 2600, the ocean system reacted in unexpected ways. Vertical instability is developing in the Southern Ocean. It causes a massive rise in deeper, warmer waters. This process is described by the authors as a “ thermal burp » – a thermal burp. Under this funny name hides a dramatic consequence. Namely: a sudden increase in the global average temperature, of around 0.2 to 0.3°C, which will continue for more than a century.

“ What we are seeing is a delayed and abrupt response to centuries of past warming », underlines Svenja Frey. This phenomenon does not constitute a return to the initial situation. It is nothing more and nothing less than a climatic counter-shock, due to the thermal memory of the oceans. Even in the absence of new emissions, this heat reappears.

The model is certainly not an absolute prediction, but it reveals the complexity of very long-term climate feedbacks. As recalled by Kirsten Zickfeld, climatologist at Simon Fraser University, cited byLiveScience“we could face major surprises in the centuries to come“.

Long-lasting consequences on the climate and vulnerable areas

Thermal release from the south could seriously penalize the southern hemisphere, already more exposed to climatic hazards. The model indicates that the induced warming would be more intense and more persistent south of the equator. Particularly in the regions surrounding the Southern Ocean. These areas, comprising a large part of developing countries, the least responsible for emissions, would suffer the most serious effects.

The rise in heat would accelerate the melting of sea ice and Antarctic ice caps. These ice caps alone contain 70% of the planet's fresh water. Their destabilization could lead to a significant rise in sea levels, with global impacts on coastal areas.

Furthermore, this thermal convection would disrupt the marine ecosystem. Species like temperature-sensitive Antarctic krill could see their habitat shrink toward more southerly latitudes. This would directly affect marine food chains, notably whales, seals and penguins, already under climatic stress.

The long-term rise in temperatures would also raise the question of the resilience of terrestrial ecosystems in the Southern Hemisphere. Prolonged droughts, heatwaves, and degradation of agricultural resources would become more frequent. Even though the countries concerned will have invested decades of effort in adapting to climate change.

This situation illustrates a profoundly inequitable climate imbalance. Once again, the regions which contribute the least to the crisis are those which risk suffering the longest and most severe consequences. This potential disaster, delayed over time, complicates any strategy of long-term anticipation and adaptation.

A questioning of long-term climate solutions

The scenario of heat release from the Southern Ocean raises a major question. Will CO₂ removal technologies be sufficient to sustainably stabilize the climate? The study reminds us that, even if negative net emissions are achieved, the heat accumulated over two centuries will remain in the deep layers of the ocean. This thermal stock, inert but powerful, could be released independently of future human efforts.

The use of negative emissions technologies, such as direct carbon capture, is still limited. These devices are expensive, rarely deployed on a large scale, and do not eliminate the effects of the warming already recorded. “Reducing our carbon load remains essential, but it is not enough if we neglect the dynamics of the oceans“, explains Ric Williams, oceanographer at the University of Liverpool.

A reassuring point, however. Yes, you have to find one. The GEOMAR model indicates that the thermal burp would not be accompanied by a massive release of CO₂ from the ocean. This avoids a double warming effect (heat + greenhouse gases). But this does not necessarily neutralize the climatic risk associated with this rise in heat.

This situation requires a review of long-term climate policies. Focusing solely on carbon neutrality objectives without considering oceanic feedbacks could prove insufficient. It is becoming urgent to integrate oceanographic parameters into global climate scenarios and to invest in the continuous monitoring of deep currents and underwater thermal structures.

Climate is not linear. It works with complex time offsets. Present actions can produce opposite effects in the very long term. Understanding and integrating this temporality into current decisions becomes essential to avoid unexpected returns from the thermal past.

Source: Ivy Frenger et al., “Southern Ocean Heat Burp in a Cooling World”.AGU Advances(2025).