In the first study of its kind, a team led by Dr Samar Khatiwala of Columbia University in New York created a mathematical model that enabled them to estimate the amount of human-generated carbon that has been sequestered by the oceans since the beginning of the Industrial Revolution.

In a paper published in Nature, they showed that while the oceans have been accumulating increasing amounts of carbon as emissions have increased, the rate of growth began to slow down during the 1980s and has dropped by ten per cent since 2000.

The researchers blame changes in the ocean’s chemistry. ‘The more carbon dioxide the ocean absorbs, the more acidic it becomes and the less carbon dioxide it can absorb,’ said Khatiwala.

The results mirror those of another study into global carbon sinks by scientists at the University of East Anglia and the British Antarctic Survey, which used 50 years of emissions data to estimate how much CO2 is being absorbed by forests, oceans and the soil.

The results of this study, published in Nature Geoscience, suggest that these natural sinks are becoming less efficient, absorbing 55 per cent of carbon now, compared with 60 per cent half a century ago. This amounts to around 400 million tonnes of carbon a year.

January 2010