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Ocean heat reached a record high for the sixth straight year

The year 2021 was the first in the United Nations’ Decade of Ocean Science for Sustainable Development Goals. This program outlines 17 goals aimed at supporting ocean science and managing oceans sustainably in the light of climate change. However, a new report from the Chinese Academy of Sciences highlights the fact that oceans are now hotter than ever, continuing their record-breaking streak for the sixth year in a row.

The report, which is authored by 23 researchers from 14 institutes, summarizes two international datasets that record observations of ocean heat content and their impact dating from the 1950s. These records were kept by NOAA and the CAS Institute of Atmospheric Physics.

“The ocean heat content is relentlessly increasing, globally, and this is a primary indicator of human-induced climate change,” said study co-author Kevin Trenberth, distinguished scholar at the National Center for Atmospheric Research in Colorado. “In this most recent report, we updated observations of the ocean through 2021, while also revisiting and reprocessing earlier data.”

Data for 2021 showed that the upper 2,000 meters in all oceans absorbed 14 more Zettajoules of heat energy than in 2020. A Zettajoule is 1021 joules, represented by a 1 and 21 zeros. This enormous quantity of energy is equal to 145 times the world’s electricity generation in 2020. In comparison, the total energy use by humans all over the world in a single year is only about half a Zettajoule. (A Zettajoule is equivalent to 240,000,000,000,000,000,000 calories.)

“As well as absorbing heat, currently, the ocean absorbs 20 to 30 percent of human carbon dioxide emissions, leading to ocean acidification; however, ocean warming reduces the efficiency of oceanic carbon uptake and leaves more carbon dioxide in the air,” said study lead author Lijing Cheng. “Monitoring and understanding the heat and carbon coupling in the future are important to track climate change mitigation goals.”

According to Cheng, significant ocean warming has occurred everywhere, in all oceans of the world, since the 1950s. It is true that there are regional warming and cooling phenomena, known as El Niño and La Niña, in certain ocean systems, and that these are natural events. They can produce heat waves that have huge impacts on marine life and may cause local extinctions of species. These regional episodes are short-lived, however, and are different from the slow and continuous increases in water temperature associated with global warming.

“Our previous work showed that scientists need less than 4 years of ocean heat measurements to detect a human-induced warming signal from natural variations.  This is much shorter than the nearly three decades of measurements required to detect global warming using temperatures of air near the Earth’s surface. Indeed, although in the top ten warmest years, global surface temperatures for 2021 are not the highest on record because of La Niña conditions in the tropical Pacific, among other things. Ocean heat content is one of the best indicators of climate change,” said Professor John Abraham from the University of St. Thomas. 

“With model experiments, our study shows that the pattern of ocean warming is a result of human-related changes in atmospheric composition,” said Cheng. “As oceans warm, the water expands and sea level rises. Warmer oceans also supercharge weather systems, creating more powerful storms and hurricanes, as well as increasing precipitation and flood risk.”

Study co-author Professor Michael Mann noted that the oceans are absorbing most of the heating from human carbon emissions. “Until we reach net zero emissions, that heating will continue, and we’ll continue to break ocean heat content records, as we did this year. Better awareness and understanding of the oceans are a basis for the actions to combat climate change.”

The report is published in the journal Advances in Atmospheric Sciences.

By Alison Bosman, Staff Writer

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