Ocean heatwaves devastate wildlife, worse to come

Invisible to people but deadly to marine life, ocean heatwaves have damaged ecosystems across the globe and are poised to become even more destructive, according to the first study to measure worldwide impacts with a single yardstick.

The number of marine heatwave days has increased by more than 50 percent since the mid-20th century, researchers reported in the journal Nature Climate Change. "Globally, marine heatwaves are becoming more frequent and prolonged, and record-breaking events have been observed in most ocean basins in the past decade," said lead author Dan Smale, a researcher at the Marine Biological Association in Plymouth, Britain.

Above the ocean watermark, on Earth’s surface, 18 of the last 19 years have been the warmest on record, leading to more severe storms, droughts, heatwaves and flooding. "Just as atmospheric heatwaves can destroy crops, forests and animal populations, marine heatwaves can devastate ocean ecosystems," Smale told AFP.

Compared to hot spells over land, which have claimed tens of thousands of lives since the start of the century, ocean heatwaves have received scant scientific attention. But sustained spikes in sea-surface temperatures can also have devastating consequences.

A 10-week marine heatwave near western Australia in 2011, for example, shattered an entire ecosystem and permanently pushed commercial fish species into colder waters. Corals have been the marquee victims of shallow-water heatwaves, and face a bleak future. Even if humanity manages to cap global warming at 1.5 degrees Celsius -- mission impossible, according to some scientists -- up to 90 percent of corals are likely to die, the UN’s top climate science body said in October.