The Ocean Carbon Sink Is Ailing

"The world's oceans act as an important sink for carbon dioxide (CO₂). To date, they have absorbed around a quarter of human-induced CO₂ emissions from the atmosphere, thereby stabilizing the global climate system. Without this sink, the CO₂ concentration in the atmosphere would be much higher and global warming would have already significantly exceeded the 1.5-degree warming limit set by the 2015 Paris Agreement. At the same time, the oceans absorb around 90% of the excess planetary heat that's building up from global warming."

"Extreme sea surface temperatures in 2023 resulted in high CO₂ outgassing, particularly in the North Atlantic, meaning that the global ocean absorbed less CO₂ overall. Thanks to El Niño, much less CO₂ than usual escaped into the atmosphere in the eastern Pacific, but the outgassing in the North Atlantic negated the positive effect. The fact that the ocean did not lose even more CO₂ is due to physical and biological processes that limited outgassing despite the record-high temperatures."

"An international research team, led by Swiss Federal Institute of Technology Zurich (ETH Zurich), investigated for the first time whether and how the extreme ocean temperatures recorded two years ago impacted this crucial carbon sink, based on oceanic CO₂ measurements from a global observation network. The study is one of the first to draw on actual observations as a foundation for insights into the behavior of a warming ocean."

Extreme sea surface temperatures in 2023 produced substantial CO₂ outgassing, notably in the North Atlantic, which reduced the ocean's net CO₂ uptake. Concurrent El Niño conditions suppressed outgassing in the eastern Pacific, but North Atlantic emissions offset that reduction. Physical and biological processes limited additional outgassing despite record-high temperatures, preventing a larger loss of oceanic CO₂. CO₂ observations from research vessels, cargo ships, buoys, and satellites were combined with machine learning to produce global estimates. The ocean continues to absorb a significant fraction of human CO₂ emissions and most excess heat. It remains uncertain whether compensating processes will persist as global warming advances.

Read at State of the Planet