The number of heatwaves affecting the planet’s oceans has increased sharply, scientists have revealed, killing swathes of sea-life like “wildfires that take out huge areas of forest.”
The damage caused in these hotspots is also harmful for humanity, which relies on the oceans for oxygen, food, storm protection and the removal of climate-warming carbon dioxide the atmosphere, they say.
Global warming is gradually increasing the average temperature of the oceans, but the new research is the first systematic global analysis of ocean heatwaves, when temperatures reach extremes for five days or more.
The research found heatwaves are becoming more frequent, prolonged and severe, with the number of heatwave days tripling in the last couple of years studied. In the longer term, the number of heatwave days jumped by more than 50 percent in the 30 years to 2016, compared with the period of 1925 to 1954.
As heatwaves have increased, kelp forests, seagrass meadows and coral reefs have been lost. These foundation species are critical to life in the ocean. They provide shelter and food to many others, but have been hit on coasts from California to Australia to Spain.
“You have heatwave-induced wildfires that take out huge areas of forest, but this is happening underwater as well,” said Dan Smale at the Marine Biological Association in Plymouth, UK, who led the research published in Nature Climate Change. “You see the kelp and seagrasses dying in front of you. Within weeks or months they are just gone, along hundreds of kilometers of coastline.”
As well as quantifying the increase in heatwaves, the team analyzed 116 research papers on eight well-studied marine heatwaves, such as the record-breaking “Ningaloo Niño” that hit Australia in 2011 and the hot “blob” that persisted in the north-east Pacific from 2013 to 2016. “They have adverse impacts on a wide range of organisms, from plankton to invertebrates, to fish, mammals and seabirds,” Smale said.
The scientists compared the areas where heatwaves have increased most with those areas harboring rich biodiversity or species already near their temperature limit and those where additional stresses, such as pollution or overfishing, already occur. This revealed hotspots of harm from the north-east Atlantic to the Caribbean to the western Pacific. “A lot of ocean systems are being battered by multiple stresses,” Smale said.