2021 Ocean Temperatures Were Warmest on Record

Meltwater cascades down a waterfall on Aug. 12, 2021 near Landvegur, Iceland, where climate change has caused a continued and strong reduction in ice caps and contributed to sea level rise. Photo credit: Sean Gallup / Getty Images

The world’s oceans reached record temperatures in 2021, despite a La Niña event that typically has a cooling influence. 

The new record was announced in a study published in Advances in Atmospheric Sciences Tuesday. This is the sixth year in a row that the ocean heat record has been broken, The Guardian reported.

“The ocean heat content is relentlessly increasing, globally, and this is a primary indicator of human-induced climate change,” study co-author and National Center for Atmospheric Research climate scientist Kevin Trenberth told The Guardian. 

Ocean heat content is a better indicator of global warming than atmospheric temperature, CNN explained, because natural cycles like La Niña have less of an impact on ocean temperatures than air temperatures. That said, it is notable that the record was broken despite the fact that La Niña encourages cooler temperatures in the Pacific. 
The world’s oceans absorb 90 percent of the excess heat trapped in the atmosphere by the burning of fossil fuels. The researchers measured these impacts in the upper 2,000 meters (approximately 6,562 feet) of the ocean, where the bulk of warming occurs, The Guardian reported. They found that this region absorbed 14 more zettajoules in 2021 than in 2020, which is 145 times greater than all the electricity generated in the world.

The scientists used a network of buoys to record these measurements, The Washington Post reported. 

The oceans have been steadily warming over time, with each decade since 1958 recording hotter temperatures. However, the pace of change has picked up since the late 1980s, when the oceans began to warm at a rate eight times faster than before. 

“When you have this long-term upward trend, you’re getting records broken almost every year, and it’s this monotonous increase,” study co-author and University of St. Thomas in Minnesota professor John Abraham told The Washington Post. “We’ve built up so much greenhouse gas that the oceans have begun to take in an increasing amount of heat, compared to what they previously were.”

All of this has real consequences. Warmer oceans fuel more intense tropical storms, such as 2021’s Hurricane Ida. They also increase the air temperature, which can lead to extreme weather events such as heavy rainfall or the tornadoes that struck several U.S. states in December. 

Finally, warmer water temperatures lead to more sea level rise, because warm water expands. In fact, the warming of ocean temperatures accounts for about a third of 20th century sea level rise, CNN reported. This increases the risk of tidal flooding, saltwater intrusion and storm surges. 

The only way to put an end to these negative consequences is to rapidly reduce greenhouse gas emissions. Acting as soon as possible is essential, because the ocean will continue to warm even after all emissions are stopped.

“We want to stress that global warming is actually ocean warming, and ocean warming has serious consequences,” study lead author and Institute of Atmospheric Physics at the Chinese Academy of Sciences climate and environmental science professor Lijing Cheng told CNN. “Ocean warming keeps breaking records, which is a reminder that the world needs action to combat climate change.”

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