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Yellow hair jellyfish and diver in front of an iceberg on the East Greenland coast
Photo: Photographer: Tobias Friedrich / Tobias Friedrich
Ocean warming rose to a new record in 2021 - it's the sixth year in a row. This is what an international research group, predominantly from the USA and China, reports in the specialist journal “Advances in Atmospheric Sciences”. Their respective estimates of the amount of heat in the world's oceans differ somewhat due to differences in allocation, data quality and coverage, but both show a clear trend.
In addition to the melting of polar ice masses, warmer ocean water is one of the reasons for the global rise in sea levels because warmer water expands. "Warmer oceans also charge weather systems, which leads to stronger storms and hurricanes and increases the risk of precipitation and flooding," said first author Lijing Cheng from the Institute for Atmospheric Physics (IAP) of the Chinese Academy of Sciences in a statement from his institution.
According to the IAP data, 14 zettajoules (trillion joules; 10 to the power of 21 joules) of thermal energy were added in the upper 2000 meters of the oceans in 2021.
According to calculations by the US National Oceanic and Atmospheric Administration (NOAA), it was even 16 zettajoules.
Both values led to new heat records in the world's oceans with a total energy content of 235 zettajoules (IAP) and 227 zettajoules (NOAA).
According to the research team, computer simulations show that the increase in heat is largely due to man-made climate change.
Big exception in the North Atlantic
"The oceans absorb most of the warming from human carbon emissions," says co-author Michael Mann of Pennsylvania State University in University Park.
There will be more and more record values until mankind reaches a net zero amount of greenhouse gas emissions, he emphasizes.
First author Cheng adds: "The ocean not only absorbs heat, it currently also absorbs 20 to 30 percent of human carbon dioxide emissions, which leads to acidification of the oceans." However, the warming of the oceans reduces the efficiency of carbon uptake, so that more carbon dioxide is in the air remain.
Overall, the Atlantic is warming more than the other oceans. But there is one exception: in a large area south of Iceland and west of the British Isles, the water has cooled in recent decades. The scientists explain this with changes in the so-called Atlantic Meridional Overturning Circulation (AMOC) and the cooling effect of aerosols - i.e. suspended particles - from industrial plants.
According to the researchers, global warming of the oceans continued in 2021, although the circulation system in the Pacific changed from an El Niño phase to a La Niña phase in the second half of 2020.
This transition is associated with unusual warming of ocean surfaces in the tropical Pacific, causing heat to escape from the ocean into the atmosphere.
During a La Niña phase, however, the warming of the oceans increases again.
By Stefan Parsch, dpa
