Extreme Heat in the Oceans Is Out of Control

Without the ocean, climate change on land would be even more catastrophic. The seas have absorbed over 90 percent of the excess heat from greenhouse gas emissions, essentially saving humanity from itself. But it’s taking a toll: The ocean, too, is rapidly warming. And just as we have heat waves on land, parts of the ocean can experience temperature spikes too.

New research exposes just how bad the problem has gotten. Researchers from the Monterey Bay Aquarium began their calculation by analyzing surface temperature data from 1870 to 1919, sampled from across the globe. (Yes, ships have been taking the ocean’s temperature for 150 years.) Once they knew the historical high temperatures for each month in different parts of the ocean, they had a baseline for marine temperature extremes before the escalation of climate change. In the 19th century, only 2 percent of the ocean surface experienced such extremes.

Then they compared this data to readings in the same places taken from 1920 to 2019. Their results show that by the year 2014, half of the ocean surface was logging temperatures once considered extreme—exceeding those historical highs. By 2019, that figure was 57 percent. In 150 years, the occurrence of extreme heat had become the new normal.

These spikes are different from the overall rise in water temperature, which is also caused by global warming. For one thing, a particular region can come back down off of a high when winter arrives. And the location of the spikes can vary over time, meaning some places were affected earlier than others. So while half the ocean surface was logging temperature extremes by 2014, the South Atlantic had actually crossed that threshold back in 1998.“And that is ludicrous,” says ecologist Kyle Van Houtan, president and CEO of the Loggerhead Marinelife Center, who coauthored today’s paper in the journal PLOS Climate describing the findings. (Van Houtan did the research in his previous role as the chief scientist at the aquarium, with marine biologist Kisei Tanaka, now at the National Oceanic and Atmospheric Administration.) “There's some major changes going on right now in the ocean, and we think that this calculation, this index, of marine heat that we built is helping to describe why,” he continues. “I think extreme marine heat is much more of a problem than we thought it was. It's actually common today, which is scary, because historically it was just extreme—it was rare.”“The trends they're seeing are consistent with results from a lot of other papers that conclude that marine heat waves are becoming more frequent, they're warmer, and they're lasting longer,” says Bridget Seegers, an oceanographer at NASA, who wasn’t involved in the work. (She was, though, among the researchers who recently reported that 2021 was the sixth hottest year ever recorded .)

Courtesy of Monterey Bay Aquarium