World’s oceans have warmed to a ‘point of no return’

More than half the global ocean sees temperature extremes that 100 years ago were rare

From 2013 to 2016, a mass of sweltering water in the eastern Pacific Ocean — known as the Blob — wreaked havoc on marine ecosystems. This illustration shows how unusually hot the waters were in May 2015. The deepest red represents 3 degrees Celsius above average.

Chelle Gentemann, Charles Thompson and Jeffrey R. Hall/PO.DAAC/JPL

What were scorching ocean extremes only recently are now normal, a new study reports. It analyzed ocean surface temperatures for the past 150 years. By 2019, it now reveals, 57 percent of the ocean’s surface was warming to temps rarely seen 100 years ago.

Authors of the study shared their new findings February 1 in PLOS Climate.

Marine ecologists wanted to learn how often modern extreme-heat events occur. They also wanted to see how long they last. Kisei Tanaka was one of those ecologists. He now works for the National Oceanic and Atmospheric Administration, or NOAA, in Honolulu, Hawaii. Tanaka teamed up with Kyle Van Houtan, who works at the Loggerhead Marinelife Center. It’s in Juno Beach, Fla. The two analyzed monthly sea-surface temperatures collected from 1870 through 2019. Then they mapped where and when extreme heat events had shown up, decade by decade.

By looking at monthly extremes instead of annual averages, new details emerged. The two found that over time, more and more patches of water were reaching extreme temperatures.

Then, in 2014, the entire ocean hit a “point of no return,” Van Houtan says.

Marine heat waves are defined as a patch of the ocean that sees at least five days of unusually high temperatures. Beginning in 2014, at least half of the ocean’s surface warmed more than the most extreme events seen from 1870 to 1919.

Heat waves harm ocean ecosystems. They can lead seabirds to starve. Corals can die. Kelp forests can die. And animals — from fish and whales to turtles — may have to swim long distances in search of comfortable temps.

In May 2020, NOAA announced that it was updating what climates it now considered “normal.” These values are what the agency uses to put daily weather events in a historical context. The average values from 1991 to 2020 are now higher than those from 1981 to 2010, NOAA found. 

Van Houtan says his new study shows extreme ocean warming, too, is now the norm. Much discussion on climate change, he notes, has been “about future events, and whether or not they might happen.” But what the emerging data make clear, he says, is that “extreme heat became common in our ocean in 2014. It’s a documented historical fact — not a future possibility.”

Carolyn Gramling is the earth & climate writer at Science News. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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