Fish killer: Dead fish in a "dead zone" caused by an algal bloom in the USA's Chautauqua National Wildlife Refuge.
Credit: NOAA
"Even if after a hundred years, if you stopped all carbon emissions, the ocean would still need hundreds of more years to cool," he added. "These low-oxygen areas would continue to expand and they would peak around 2,000 years from now. The ocean would then slowly recover as it cools."
Even under the less gloomy scenario, there would still be significant, long-term expansion of oxygen-starved zones.
Marine dead zones already exist today, in shallow areas next to the coast, where runoff from agricultural fertiliser causes an explosion in oxygen-gobbling algae.
Wide oxygen depletion of the ocean, though, poses a far greater threat, touching at the heart of biodiversity, the paper warns.
Mass extinction
Around 250 million years ago, a chemical change of the seas led to a massive wipeout of marine species.
Lead scientist Gary Shaffer of the Niels Bohr Institute at the University of Copenhagen said it was unclear, in the grim light of this study, whether future generations could look to the oceans as a major reserve of food.
"Reduced fossil-fuel emissions are needed over the next few generations to limit ongoing ocean oxygen depletion and acidification and their long-term adverse effects," he said.
Since 1900, the mean global atmospheric temperature has risen by 0.8 ºC the U.N.'s Intergovernmental Panel on Climate Change (IPCC) said in 2007. It forecast warming of 1.8 to 4.0 ºC by 2100 over 1980 to 99 levels, but said "positive feedback" triggers that could amplify warming remain unclear.
