The clouds of global warming don’t exactly boast a silver lining, but there is a little bonus. Melting sea ice in the Arctic is enabling ocean waters to soak up more carbon dioxide from the atmosphere. Ice retreat over the last 30 years has tripled the amount of CO2 the Arctic Ocean can absorb.

Nick Bates of the Bermuda Institute of Ocean Sciences and colleagues calculated CO2 uptake in the Arctic Ocean from measurements taken from the Chuckchi Sea and Canada basin in 2002 and 2004. They found that CO2 uptake from the atmosphere increased dramatically during the summer months, when sea ice was at a minimum (Geophysical Research Letters, DOI: 10.1029/2006GL027028).

“Sea ice acts as a barrier to gas exchange,” says Bates. Overall they calculated that the entire Arctic Ocean is currently able to absorb up to 66 million tonnes of CO2 per year. Future ice-melt may increase absorption by a further 20 million tonnes per decade. However, this won’t be enough to offset global warming: currently worldwide emissions amount to over 30 billion tonnes per year.

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