Monday, 13 June 2011

Arctic soot and sea level rise

Over the last decade or so there has been growing concern about the accelerating pace of warming in the Arctic. Billions of tons of fresh water are being shed by melting glaciers in Greenland and this MUST have major effects on the ocean currents as well as global sea level rises. (Melting of sea ice, as opposed to land ice, has no effect on sea level anymore than the melting of a block of ice in a bath raises the level of water in a bath because as the ice block gets smaller the water moves into the vacated space.)

Global warming by carbon dioxide remains a problem but in recent years another major factor has been identified as of major importance: soot.

A thin layer of black carbon, invisible to the naked eye, settling on the Arctic snow, allows it to absorb radiant heat from the Sun more rapidly. This adds to the effect of the ambient temperature rise.  The soot appears to originate from old types of diesel engine, wood- or dung-burning stoves and open burning (forest fires, slash-and-burn agriculture etc.). This could cause sea levels this century to rise much faster than previously estimated – more like 5 metres than 1 metre.

Looking on the bright side the airborne soot particles only remain aloft for up to 10 days, so any reductions in the sources of soot would very quickly reduce the rate of temperature rise due to carbon dioxide, methane and other greenhouse gases. Carbon dioxide has a much longer lifetime than airborne soot – around a century.

It also has to be born in mind that as the white area of the Earth’s land and sea surface shrinks this will cause less solar radiant heat to be reflected back into space, so that the land and sea temperatures will rise, which in turn increases the temperature of the air above.