Arctic sunshine cranks up threat from greenhouse gases

IT'S a solar double whammy. Not only does sunlight melt Arctic ice, but it also speeds up the conversion of frozen organic matter into carbon dioxide.

The amount of carbon in dead vegetation preserved in the far northern permafrost is estimated to be twice what the atmosphere holds as CO₂. Global warming could allow this plant matter to decompose, releasing either CO₂ or methane ? both greenhouse gases. The extent of the risk remains uncertain because the release mechanisms are not clear.

Rose Cory at the University of North Carolina at Chapel Hill and her colleagues analysed water from ponds forming on melting permafrost at 27 sites across the Arctic. They found that the amount of CO₂ released was 40 per cent higher when the water was exposed to ultraviolet light than when kept dark. This is because UV light, a component of sunlight, raises the respiration rate of soil bacteria and fungi, amplifying the amount of organic matter they break down and the amount of CO₂ released.

The thawing Arctic is emerging as a potentially major source of positive feedback that could accelerate global warming beyond existing projections. "Our task now is to quantify how fast this previously frozen carbon may be converted to CO₂, so that models can include the process," Cory says.

Journal reference: PNAS, DOI: 10.1073/pnas.1214104110.

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