OSLO - The world's oceans are under greater threat than previously believed from a "deadly trio" of global warming, declining oxygen levels and acidification, an international study said on Thursday.
The oceans have continued to warm, pushing many commercial fish stocks towards the poles and raising the risk of extinction for some marine species, despite a slower pace of temperature rises in the atmosphere this century, it said.
"Risks to the ocean and the ecosystems it supports have been significantly underestimated," according to the International Programme on the State of the Ocean (IPSO), a non-governmental group of leading scientists.
"The scale and rate of the present day carbon perturbation, and resulting ocean acidification, is unprecedented in Earth's known history," according to the report, made with the International Union for Conservation of Nature.
The oceans are warming because of heat from a build-up of greenhouse gases in the atmosphere. Fertilizers and sewage that wash into the oceans can cause blooms of algae that reduce oxygen levels in the waters. And carbon dioxide in the air can form a weak acid when it reacts with sea water.
"The 'deadly trio' of ... acidification, warming and deoxygenation is seriously affecting how productive and efficient the ocean is," the study said.
Alex Rogers of Oxford University, scientific director of IPSO, told Reuters scientists were finding that threats to the oceans, from the impacts of carbon to over-fishing, were compounding one another.
"We are seeing impacts throughout the world," he said.