Global Warming

Ocean heatwaves devastate wildlife

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.

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.

But other bedrock species have suffered too: the 2011 surge of heat killed off large swathes of seagrass meadows and kelp forests, along with the finfish and abalone that depend on them.

Another ocean hot spell off the coast of California warmed waters by 6 C (10.8 F) and lasted for more than a year. Known at "The Blob", it generated toxic algae blooms, caused the closure of crab fisheries, and led to the death of sea lions, whales and sea birds.

As manmade global warming heats the planet, oceans have absorbed some 90 percent of the extra heat generated. Without that heat sponge, air temperatures would be intolerably higher.