Antarctica – September 13, 2026
As the world pursues ambitious climate targets and prepares for potential future carbon removal, a new study reveals an unexpected consequence: the Southern Ocean around Antarctica could stop absorbing atmospheric carbon dioxide and start releasing it.
The research, published September 2, 2026, in the journal Science Advances, uses climate simulations to explore what happens when emissions decline to net zero and even become negative. Under these mitigation scenarios, the Southern Ocean's role as a critical carbon sink may reverse, potentially undermining decades of emissions reduction efforts.
The Southern Ocean currently accounts for 40% to 50% of all carbon dioxide absorbed by the world's oceans, making it one of the planet's most important natural buffers against climate change. Colder waters dissolve CO2 from the atmosphere and transport it into deeper layers, locking it away for centuries.
How the Flip Could Happen
The study authors, led by Huiji Lee and Jong-Seong Kug, ran two idealized long-term emissions scenarios to test the Southern Ocean's response. The first scenario reaches net-zero emissions by mid-century, while the second continues beyond that point with sustained negative emissions through direct air capture technologies.
The simulations showed that once emissions begin declining, the Southern Ocean rapidly loses its ability to absorb CO2. Over time, surface waters gradually shift from net absorbers to net sources of atmospheric carbon dioxide. In the negative emissions scenario, this reversal was projected to occur around 2154, persisting for decades.
The researchers identified two main drivers for this unexpected shift. First, persistent warming of Southern Ocean surface waters reduces the water's capacity to dissolve CO2, since warm water holds less gas than cold water. Second, declining alkalinity in seawater weakens the ocean's chemical ability to absorb and buffer atmospheric carbon.
"The temporal evolution of the globally averaged ocean-atmosphere CO2 flux is characterized by enhanced oceanic CO2 uptake until the emission peak is reached (approximately year 2050), followed by weakened uptake as the emissions decline. In the NEG experiment, this weakening continues, and in the year 2154, the ocean transitions from a net sink to a net source of CO2." — Huiji Lee, lead author, published in Science Advances, September 2026
Delayed Response, Long-Term Risks
The reversal doesn't happen immediately when emissions peak. The study found that atmospheric CO2 levels can continue declining while the Southern Ocean gradually transitions toward becoming a carbon source. This delayed response occurs because ocean physics and chemistry operate on different timescales than atmospheric concentrations.
Even after negative emissions cease and atmospheric CO2 returns to initial levels, the simulations showed the Southern Ocean remained a net carbon source for an extended period. This persistence suggests the ocean's climate response involves long-term feedback processes that could continue beyond active mitigation efforts.
Implications for Climate Policy
The finding carries significant implications for global climate strategy. Many current climate models and policy frameworks assume the Southern Ocean will continue absorbing carbon as emissions decline, providing ongoing support for global carbon budgets. If the ocean begins releasing stored carbon instead, those calculations would need revision.
The research team emphasized that this is a modeling result that requires confirmation through observational data. The study relied on one ocean-climate model, and the authors noted it does not account for Antarctic ice-sheet dynamics, which could influence Southern Ocean circulation patterns and carbon uptake in the future.
Ocean Carbon Cycle Uncertainties
The Southern Ocean is one of the most challenging regions to model accurately. It experiences intense storms, complex sea ice dynamics, and powerful currents that interact with atmospheric conditions in ways that are difficult to capture in global climate models. Recent observations have shown the Southern Ocean is already absorbing carbon at a slower rate than projected, suggesting natural variability may be more influential than previously understood.
The researchers called for continued monitoring of Southern Ocean CO2 fluxes to test their findings. Long-term observations from research stations around Antarctica and from autonomous sensors on drifting buoys will be essential to determine whether the simulated reversal matches reality.
This study comes as the global community prepares for the next rounds of climate negotiations under the Paris Agreement. With nations evaluating their contributions and considering ambitious net-zero and net-negative targets, understanding the full complexity of the Earth's carbon cycle becomes increasingly urgent.
Source: Science Advances, September 2, 2026. Phys.org, September 12, 2026.
FIRAT Editorial Board
Institutional Research Desk · Foresight Institute of Research and Translation
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