Potential Carbon Release from Southern Ocean
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Human-induced global warming is disrupting the Atlantic Meridional Overturning Circulation (AMOC), a critical ocean current system that includes the Gulf Stream, responsible for warming Europe. A total shutdown of the AMOC could trigger a massive release of carbon from deep Antarctic waters into the atmosphere, exacerbating global warming.
Research indicates that an AMOC collapse can lead to severe climatic consequences, including colder winters in Europe and disrupted monsoons in Africa and Asia, while also increasing global temperatures. Recent computer models predict that this scenario could release 640 billion tonnes of carbon dioxide near the South Pole, raising global temperatures by an additional 0.2°C.
“The collapse of the AMOC may trigger large-scale mixing in the Southern Ocean, releasing carbon stored in deep waters,” states Danian, a researcher at the Potsdam Institute for Climate Impact Research. “This outcome is unprecedented.”
The co-authors emphasize that potential catastrophic events can have even more severe implications than previously understood. As Johan Rockström, also from the Potsdam Institute, notes, “We must remain vigilant, as one failure can trigger a domino effect.”
The AMOC operates by transporting warm, salty water from the Gulf of Mexico to the North Atlantic, where it cools, sinks, and circulates back southward along the ocean floor. Scientists believe that increased fresh meltwater from the Greenland ice sheet is diluting the AMOC, thereby slowing its sinking process.
Recent buoy measurements reveal a weakening return flow, suggesting a 15% decline in the AMOC, with models predicting a potential collapse within decades to centuries.
A new study exploring AMOC collapse under varying climate scenarios shows that if atmospheric CO2 levels exceed 350 ppm, the AMOC fails to recover after shutdown. Given the current CO2 level of 430 ppm, this indicates that AMOC decay may be irreversible.
The study also identified that if the AMOC, a key component of the global ocean current conveyor belt connecting the Southern Ocean and Pacific Ocean, collapses, it could lead to deep water convection near the South Pole. This deep water rests under a layer of fresher surface water, where carbon accumulates from both atmospheric CO2 and decaying plankton. The model suggests a significant portion of this carbon would be released into the atmosphere.
Previous research indicates that past AMOC collapses similarly triggered convection near the South Pole, aligning with evidence that the Southern Ocean is becoming less salty. This reduction in salinity disrupts the layered structure above the saltier deep water, facilitating surface access for deep water.
“It’s striking to observe these changes in such a warm climate amid rising CO2 levels,” says Jonathan Baker from the Met Office. “This study is intriguing, yet its findings depend on whether convection in the Southern Ocean intensifies; different models exhibit varied responses, leading to ongoing uncertainties.”
The study also forecasts that AMOC collapse could cool the Arctic by 7 degrees Celsius, freezing regions in Canada, Scandinavia, and Russia while concurrently warming Antarctica by 6 degrees Celsius. The West Antarctic Ice Sheet remains at risk of surpassing its tipping point, which could trigger a larger collapse of the East Antarctic Ice Sheet, resulting in significant sea level rises.
The repercussions of CO2 emissions could persist for over a millennium following any AMOC closure. However, Rockström cautions that continued greenhouse gas emissions may lock in a future collapse of the AMOC in just a few decades.
“The window for change could be as short as the next 25 to 50 years,” he warns. “It’s vital to recognize the urgency; it’s not just about the timing of impacts, but about our commitment to preventing an increasingly inhospitable planet for future generations.”
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Source: www.newscientist.com
