Scientists analyzed satellite-based measurements of sea surface temperature from 1982 to 2016 and found that the frequency of marine heatwaves had doubled. These extreme heat events in the ocean’s surface waters can last from days to months and can occur across thousands of kilometres.
If average global temperatures increase to 3.5 °C above pre-industrial levels by the end of the century, as researchers currently project, the frequency of ocean heatwaves could increase by a factor of 41. In other words, a 1-in-100-day event at pre-industrial levels of warming could become a 1-in-3-day event.
“Marine heatwaves have already become more long-lasting, frequent, intense and extensive than in the past,” says lead study author Thomas Frölicher, a climatologist at the University of Bern in Switzerland. He adds that these changes are already well outside what could be expected on the basis of natural swings in Earth’s climate: the study’s analysis determined that 87% of heatwaves in the ocean are the result of human-induced global warming.
Episodes include the massive warm water ‘blob’ in the northeastern Pacific Ocean that killed off sea otters in Alaska and sea lions in California, and disrupted fisheries off North America from 2014 to 2015. They also included the massive 2015–16 El Niño that ravaged coral reefs around the world.
Ocean heatwaves will become more frequent and extreme as the climate warms, scientists report on August 15 in Nature. These episodes of intense heat could disrupt marine food webs and reshape biodiversity in the world’s oceans.