Yesterday’s scorching ocean extremes are today’s new normal. A new analysis of surface ocean temperatures over the past 150 years reveals that in 2019, 57 percent of the ocean’s surface experienced temperatures rarely seen a century ago, researchers report February 1 in Climate.
In late December 2014, an undersea volcano erupted between two small islands in the Tonga volcanic arc northeast of New Zealand, sending steam and dense ash plumes high into the air. By the time the eruption ended about 5 weeks later, a new island had formed, eventually bridging the gap between the original islands. Winds and ocean waves then began rapidly reshaping the newly emerged volcanic cone.
Ten months after the eruption, we visited the new island, which we unofficially nicknamed Island. There, we attempted to characterize the volcano logy of the eruption, begin tracking the rate of erosion on the new island, and assemble a history of volcanism in this region of the southwest Pacific. Our findings reveal a shallow submarine volcanic caldera adjacent to the new volcanic island, and they highlight how incomplete the volcanic record can be at remote oceanic volcanoes.
To provide context for the frequency and duration of modern extreme heat events, marine ecologists Tanaka, now at the National Oceanographic and Atmospheric Administration in Honolulu, and Kyle Van, now at the Loggerhead Marine life Center in Juno Beach, Fla., analyzed monthly sea-surface temperatures from 1870 through 2019, mapping where and when extreme heat events occurred decade to decade.
Looking at monthly extremes rather than annual averages revealed new benchmarks in how the ocean is changing. More and more patches of water hit extreme temperatures over time, the team found. Then, in 2014, the entire ocean hit the “point of no return,” Van says. Beginning that year, at least half of the ocean’s surface waters saw temperatures hotter than the most extreme events from 1870 to 1919.
Marine heat waves are defined as at least five days of unusually high temperatures for a patch of ocean. Heat waves wreak havoc on ocean ecosystems, leading to seabird starvation, coral bleaching, dying kelp forests, and migration of fish, whales and turtles in search of cooler waters
In May 2020, NOAA announced that it was updating its “climate normal” — what the agency uses to put daily weather events in historical context — from the average 1981–2010 values to the higher 1991–2020 averages (SN: 5/26/21).
This study emphasizes that ocean heat extremes are also now the norm, Van says. “Much of the public discussion now on climate change is about future events, and whether they might happen,” he says. “Extreme heat became common in our ocean in 2014. It’s a documented historical fact, not a future possibility.”
In hot water,
A new analysis of monthly sea surface temperatures across the global ocean reveals how more and more patches of ocean saw heat extremes every year. These four decal snapshots show temperature shifts since 1980. Beginning in 2014, more than half of the ocean began to reach extremes hotter than even the most extreme events from 1870 to 1919.
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