The oceans play a critical role in reducing global warming by absorbing carbon dioxide emissions. But the researchers found that as the oceans warm in the future, their ability to absorb CO2 may decrease, leading to even more warming. In a study by the University of Texas at Austin, scientists found, based on climate simulations adjusted for worst-case, that the oceans’ ability to absorb carbon dioxide (CO2) will peak by 2100 and drop to half its current efficiency by 2300. emission scenarios

The decline is due to the formation of a low alkalinity water surface layer that inhibits the oceans’ ability to absorb CO2. Alkalinity is a chemical property that affects how much CO2 can dissolve in seawater. The authors say that although the emissions scenario used in the study is highly unlikely due to global efforts to limit greenhouse gas emissions, the results reveal a previously unknown tipping point and its activation will result in a significant brake on global warming.

Megumi Chikamoto, who led the work as a research scientist at the university, said: “We need to consider these worst-case scenarios to understand how our CO2 emissions could affect not just this century, but the next and the next.” Said. Texas Institute of Geophysics.

The oceans today absorb about a third of the CO2 emitted by humans. Previously, climate modeling had shown that the oceans slowed down CO2 absorption over time, but no one had seen alkalinity as an explanation. To arrive at their conclusions, the researchers scanned parts of 450 years of simulation until they identified alkalinity as the main cause of the slowdown.

The impact begins with extreme climate change, which increases precipitation and slows ocean currents, according to the findings. This covers the surface of the oceans with a layer of warm freshwater that does not readily mix with the colder, more alkaline water below. As this surface layer becomes more saturated with CO2, its alkalinity and with it its ability to absorb CO2 decreases. The end result is a surface layer that acts as a barrier against CO2 absorption. This means less greenhouse gases enter the ocean and more remain in the atmosphere. This results in faster heating, which supports and strengthens the low alkalinity surface layer.

Co-author Pedro DiNezio, an assistant researcher at the University of Texas Institute of Geophysics and an associate professor at the University of Colorado, said the discovery is a powerful reminder that the world must cut CO2 emissions to avoid crossing this and other tipping points.

“Whether this is the collapse of the ice sheets, there is potentially a series of related crises in our future and we must avoid at all costs,” he said. He said the next step is to determine if the alkalinity mechanism works under more moderate emission scenarios.

University of Colorado professor and co-author Nikki Lovenduski, who contributed to the Intergovernmental Panel on Climate Change’s 2021 climate report, said the study’s findings will help scientists make better predictions about future climate change.

“This article shows that the problem of climate change may be exacerbated by things that are not yet known,” he said. “But the ocean-climate feedback mechanism revealed by this particular study will open up new avenues of research that will help us better understand the carbon cycle, past climate change, and perhaps find solutions to future problems.”