The Southern Ocean currently absorbs about 10% of human caused carbon emissions, but researchers say it could become a net source of carbon dioxide if atmospheric CO2 concentrations begin to decline after global net zero emissions are achieved.
The Southern Ocean, the world’s largest regional carbon sink, could eventually begin releasing more carbon dioxide into the atmosphere than it absorbs once global emissions reach net zero and atmospheric CO2 levels fall, according to a new study reported by New Scientist.
The finding highlights a major challenge for efforts to reverse climate change. Researchers say the ocean’s response to declining atmospheric carbon dioxide could prolong global warming for centuries, even if humanity succeeds in removing enormous quantities of CO2 from the atmosphere.
The Southern Ocean currently plays a critical role in regulating the global climate. It absorbs more carbon dioxide than any other single ocean region and is estimated to take up around 10% of human caused emissions. Strong winds and storms help drive the movement of carbon from the atmosphere into the ocean, making the region an important natural buffer against global warming.
However, this process could change as atmospheric CO2 concentrations decline.
According to the study, once humanity reaches net-zero emissions and atmospheric carbon dioxide begins falling, the Southern Ocean may gradually release some of the carbon it has accumulated back into the atmosphere. This natural feedback could reduce the effectiveness of efforts to lower atmospheric CO2 and slow the rate at which global temperatures decline.
The findings are particularly significant as governments and scientists increasingly consider carbon dioxide removal as a way to tackle climate change. Technologies and nature based approaches designed to remove CO2 from the atmosphere are expected to play a role in future climate strategies.
But the study suggests that removing carbon from the atmosphere may not immediately translate into an equivalent reduction in long term warming. Changes in the atmosphere ocean carbon balance could cause the oceans to release stored carbon as atmospheric concentrations fall.
Researchers warn that this feedback could keep temperatures elevated for much longer than previously expected.
The implications extend beyond the Southern Ocean. Natural systems that currently absorb large quantities of carbon could respond differently in a world where atmospheric CO2 concentrations are declining. Understanding these feedbacks will therefore be crucial for assessing how quickly the planet could cool after emissions are brought under control.
The research does not suggest that reaching net zero would be ineffective. Instead, it underlines the importance of rapidly reducing greenhouse gas emissions while recognising that returning the climate system to its earlier state will be considerably more difficult than simply stopping additional emissions.
The findings reinforce a broader message emerging from climate research achieving net zero is likely to be a milestone rather than the end of the climate challenge. Even after emissions fall to zero, interactions between the atmosphere, oceans and other natural carbon reservoirs could continue influencing global temperatures for centuries.