Climate science: the gathering storm
July 23rd 2012
After the driest winter on record, Sir David Attenborough wouldn’t be the only Briton to blame the wettest English summer ever on global climate change, on some inexorable shift in the planetary machinery that upsets all reasonable expectation. There is a connection, although no single meteorological episode in any locality could ever be directly linked to global warming: this flood or that cyclone might have happened anyway. Even the increasing frequency worldwide of climate-related disasters, along with the lives, homes and harvests lost, cannot be entirely blamed on the steady increase in carbon dioxide levels in the atmosphere. Population growth and economic development each year deliver more potential victims, with more to lose. Finally, the measured increase in the intensity of extreme events – ever fiercer heatwaves, ever more violent floods – rests on an uncertain premise: if systematic weather records in many parts of the world are barely a century old, what does it mean to declare something ‘the worst ever’ or a ‘once in a century’ flood?
So much for the caution: now for the observed reality of atmospheric physics. If average temperatures increase, so will temperature extremes. As temperatures increase, so will evaporation. As evaporation increases, so will precipitation. As tropical seas get warmer, so will the increased hazard of cyclone, hurricane or typhoon. Nine of the 10 warmest years on record have occurred in this century. Last year was the second rainiest year on record worldwide; the winner of this dubious derby was 2010, which, with 2005, was also the warmest on record. A springtime hosepipe ban in southern England was promptly followed by unprecedented rain and flooding in much of the country. Some of the most catastrophic floods and lethal heatwaves ever observed have claimed many thousands of lives in the last decade, and the increasing probability of such extremes has been predicted again and again: by the World Meteorological Organisation; by the Intergovernmental Panel on Climate Change; by the UN’s inter-agency secretariat for disaster reduction; and by researchers at the Potsdam Institute for Climate Impact Research in Germany who have listed the 19 hottest, wettest or stormiest ever events, all in the last decade. There are other, less direct indicators. The northern hemisphere growing season has expanded by 12 days since 1988. Sea levels are rising. Higher sea levels make storm surges – and consequent catastrophic floods in estuaries, flood plains and coastal cities – more likely, more costly and more deadly. The signals are clear enough. Climate is changing, and local weather patterns are responding. Conditions that seem bad now may be regarded as relatively benign in decades to come. Any single episode of good or bad weather is a chance outcome, like the throw of the dice. But the dice now seem to be loaded.
Read the full article: The Guardian
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