"We have been taking the ocean for granted," states a report that warns of a "deadly trio" of ocean warming, acidification, and oxygen loss.

"We are... exposing organisms to intolerable evolutionary pressure," it said. "The next mass (species) extinction event may have already begun."

The scientific review by the International Programme on the State of the Ocean (IPSO) and the International Union for the Conservation of Nature cautioned of unprecedented ocean acidification as humans keep burning oil and coal and pump out carbon dioxide (CO2) -- about a third of which is absorbed by the sea.