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.