Ozone Recovery Boosts Carbon Uptake in Southern Ocean, Study Finds

Current research has shown that the healing of the ozone layer could possibly see the ability of the Southern Ocean to absorb carbon increase, resulting in an achievable climate dividend. But the study cautions that this desirable outcome can only occur if greenhouse gases are significantly cut worldwide. The research was conducted by the University of East Anglia and the UK National Centre for Atmospheric Science and the results were published in the journal Science Advances.

The Southern Ocean that encircles Antarctica is of significance to the planet's total carbon cycle. Although small, it sequesters an over-proportional quantity of atmospheric carbon, which acts to offset greenhouse gas warming. It is therefore of importance to determine how this may alter over the course of the next several decades in order to model climate change impacts and determine the efficacy of mitigation efforts.

The investigators sought to determine how future and historical ozone conditions and different greenhouse gas (GHG) emission possibilities affect the capability of the Southern Ocean to act as a carbon sink. With the UK Earth System Model (UKESM1), researchers could simulate three different ozone scenarios for 1950-2100. These included a world in which the ozone hole never materialized, a present-state-of-the-world simulation in which the hole started to heal following the Montréal Protocol of 1987, and one in which the hole stayed the same at 1987 levels.

Together with ozone conditions, the investigators introduced two levels of future GHG emissions: high emissions and low emissions. These simulations together enabled them to estimate how much the important ocean parameters varied over 150 years and how resulting physical changes impacted the carbon sequestration of the Southern Ocean.

Previously, the ozone layer depletion caused more intense winds in the Southern Ocean region, breaking the ocean circulation. The strengthened winds pulled carbon-rich deep waters to the surface, limiting the ocean's capacity to take up more atmospheric carbon. This effect made the Southern Ocean less effective as a carbon sink in the late 20th century.

But the research indicated that this can be turned around because the ozone layer is still recovering. Under future conditions of low greenhouse gas emissions, the impact of the ozone hole on ocean winds and carbon storage diminishes. Instead, the emissions of greenhouse gases become the dominant force in determining wind patterns and ocean processes. Under the low-emission condition, the adverse impacts of ozone loss on the Southern Ocean's carbon storage capacity are reversible.

Conversely, in the case of high emissions, a rise in greenhouse gases also strengthens winds over the Southern Ocean. This has the same effect as the historical impact of ozone depletion and results in the same level of interference with ocean circulation. Accordingly, mitigation through recovery from ozone is offset by the long-lasting impact of GHG emissions, and carbon sequestration by the Southern Ocean is less effective in controlling climate change.

The second major finding of the research is that, in the future, circulation in the oceans will be less crucial in sequestration of the ocean's carbon than it has been historically. This is based on alterations in the way carbon is moved from the surface water to the deep ocean water. As carbon accumulates in the surface waters, the ability to take up additional amounts of the same from the atmosphere decreases, regardless of changes in circulation.

This study emphasizes the imperative of synchronized global cuts in emissions in order to achieve the maximum environmental gain of ozone recovery. International treaties such as the Montréal Protocol have hitherto retarded the formation of ozone-depleting substances, but ongoing greenhouse gas emissions risk undermining that achievement.

The results clarify the interlink between stratospheric ozone and greenhouse gases in regulating the carbon balance of the Southern Ocean. Distinguishing the impact of each variable on a longer timescale, the study establishes that the future capacity of the ocean to function as a carbon sink is not only governed by natural recovery processes but equally determined by anthropogenic emissions.

This research is useful to larger climate science in the sense that it explains that environmental issues are interconnected. Successful climate mitigation means mitigating a series of challenges at once, such as the depletion of ozone and emissions reductions. Preservation of the Southern Ocean's carbon sink function is a strategy for larger efforts aimed at stopping global warming and its effects.

The research, "Decreasing importance of carbon-climate feedbacks in the Southern Ocean under a warming climate", was released on 16 May 2025 by Science Advances. It was conducted by researchers Tereza Jarníková, Corinne Le Quéré, Steven Rumbold, and Colin Jones and supported by the UK Natural Environment Research Council and the Royal Society.

Source/Credits:
Science Advances, University of East Anglia, National Centre for Atmospheric Science