Ocean 'less effective at absorbing climate change gases'

Atmospheric carbon dioxide is no longer being absorbed by the Southern Ocean at the rate it used to be, new research shows.

Each decade since 1981, the ocean has soaked up between 5 per cent and 30 per cent less of the greenhouse gas than experts had predicted.

At the same time, it has unloaded more carbon dioxide into the atmosphere.

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The findings could have grave implications for climate change. Like the rainforests, the Southern Ocean is one of the most important carbon "sinks" that together remove half of all man-made emissions of carbon dioxide.

It acts like a huge sponge, trapping carbon from the atmosphere. But the research published today in the journal Science suggests that it is becoming saturated.

An international team led by Dr Corinne Le Quere, from the University of East Anglia and British Antarctic Survey collected data on atmospheric carbon dioxide from 11 stations in the Southern Ocean and 40 others across the globe.

They calculated that the efficiency of the Southern Ocean sink was sinking. Up to 30 per cent less carbon dioxide was disappearing into the ocean each decade than had been expected.

Emissions of carbon dioxide from the ocean had actually increased by 40 per cent since 1981.

The cause of the weakened sink was an increase in winds over the ocean since 1958 that may itself have been triggered by man-made global warming, said the scientists.

Dr Le Quere said: "This is the first time that we've been able to say that climate change itself is responsible for the saturation of the Southern Ocean sink. This is serious. All climate models predict that this kind of 'feedback' will continue and intensify during this century.

"The Earth's carbon sinks - of which the Southern Ocean accounts for 15 per cent - absorb about half of all human carbon emissions. With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere."

The research suggests it might be even more difficult to stabilise levels of carbon dioxide in the atmosphere than was previously thought.

Professor Chris Rapley, director of the British Antarctic Survey, said: "Since the beginning of the industrial revolution the world's oceans have absorbed about a quarter of the 500 gigatons of carbon emitted into the atmosphere by humans.

"The possibility that in a warmer world the Southern Ocean - the strongest ocean sink - is weakening is a cause for concern."