Oceans

Global warming goes to sea — heat waves hit oceans worldwide

While much research focuses on the impacts of climate change on marine ecosystems in the near and distant future, a new study by the Monterey Bay Aquarium finds that global warming had reached a turning point in 2014, when more than half of the world’s oceans experienced extreme heat.

Using what it calls an “atlas of extreme heat” to map out global ocean temperatures over time, the study was published Tuesday in the journal PLOS Climate. It helps put into context the marine heat waves that occurred off the California coast in recent years that It’s also a reminder that climate change is not a future abstract occurrence but something that is already happening, co-author Kyle Van Houtan said.

“We weren’t shocked, but we were surprised by the distribution of extreme heat throughout the world,” said Van Houtan, a former chief scientist at Monterey Bay Aquarium. “The numbers fluctuated over time but steadily increased.” But when they crossed the threshold of 50% of the world’s oceans experiencing extreme heat, he added, “You’re at a place where what used to be extremely rare is normal.”

Marine heat waves are extended periods when sea surface temperatures stay a few degrees higher than usual. Along the California coast, the 2014-16 marine heat wave was caused by an El Niño and what was known as “the blob,” an area of ​​persistent. but they can also be caused by ocean currents or warm air and can be associated with drought on land, as was the case in California.

While half of the world’s oceans experienced marine heat waves in 2014, they became common in some areas much earlier, including the South Atlantic Ocean in 1998 and the Indian Ocean in 2007, the study found. By 2019, up to 57% of the world’s oceans experienced extreme heat.

To define extreme marine heat, Van Houtan and co-author Kisei Tanaka, a former research data scientist at Monterey Bay Aquarium, used two publicly available data sets of global sea surface temperatures that have been recorded since the 19th century. marine temperatures between 1870 and 1920 and then looked at subsequent years to see how often those baseline extreme temperatures were reached.

“We already have this great historical data set of sea surface temperature, and we can actually show that the climate change has been taking a certain type of form and showing clear signs across the global oceans,” said Tanaka, now a research marine biologist for the National Oceanic and Atmospheric Administration in Honolulu, who said the code they created for the study is publicly available for other researchers.

He and Van Houtan decided to do the study after the marine heat waves along the California coast of 2014 to 2016, which were associated with the disappearance of kelp forests and unusual wildlife migrations.

“Monterey Bay started seeing a lot of juvenile white sharks, which had been considered a very rare sighting,” Tanaka said.

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