The oceans are more acidic now than they have been for at least 300 million years, due to carbon dioxide emissions from burning fossil fuels, and a mass extinction of key species may already be on its way as a result, leading marine scientists warned on Wednesday.
An international audit of the health of the oceans has found that overfishing and pollution are also contributing to the crisis, in a combination of destructive forces that are imperilling marine life, on which billions of people depend for their nutrition and livelihood.
In the starkest warning yet of the threat to ocean health, the International Program on the State of the Ocean (IPSO) said: “This [acidification] is unprecedented in the Earth’s known history. We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure. The next mass extinction may have already begun.”
It published its findings in the State of the Oceans report, collated every two years from global monitoring and other research studies.
Oxford University professor of biology Alex Rogers said: “The health of the ocean is spiraling downwards far more rapidly than we had thought. We are seeing greater change, happening faster, and the effects are more imminent than previously anticipated.”
Coral is particularly at risk. Increased acidity dissolves the calcium carbonate skeletons that form the structure of reefs, and rising temperatures lead to bleaching where the corals lose symbiotic algae that they rely on. The report says that world governments’ current pledges to curb carbon emissions would not go far enough or fast enough to save many reefs. There is a timelag of several decades between the carbon being emitted and the effects on seas, meaning further acidification and warming of the oceans are inevitable.
Corals are vital to the health of fisheries, because they act as nurseries to young fish and smaller species that provide food for bigger ones.
Carbon dioxide in the atmosphere is absorbed by the seas and makes them more acidic. IPSO found the situation was even more dire than that laid out by top climate scientists in their landmark report last week.
In absorbing carbon and heat from the atmosphere, the world’s oceans have shielded humans from the worst effects of global warming, the marine scientists said. This has slowed the rate of climate change on land, but its profound effects on marine life are only now being understood.
Current rates of carbon release into the oceans are 10 times faster than those before the last major species extinction, which was the Paleocene-Eocene Thermal Maximum extinction, about 55 million years ago. The IPSO scientists can tell that the current ocean acidification is the highest for 300 million years from geological records.
They called for strong action by governments to limit carbon concentrations in the atmosphere to no more than 450 parts per million of carbon dioxide equivalent. That would require urgent and deep reductions in fossil fuel use.