Graph of the Day: Precipitation increase over last century

March 28, 2011

New Scientist has the article (sub required and well worth it)

There is no doubt that temperatures are rising, and basic physics suggests that warmer means wetter, because warmer air can hold more moisture.Observations confirm that the lower atmosphere holds about 5 per cent more water than a century ago, giving it that much more ammunition to unleash in a downpour or blizzard.

So does this explain the recent floods? “I don’t think it is legitimate to assume that climate change played a role in these events until we’ve done the work,” says Myles Allen of the University of Oxford. There are many types of floods, he says, and while climate change is making some extreme events more likely, others – such as floods caused by melting snow – may become less likely.

Others think we can say more. “The pervasive increase in water vapour changes the intensity of precipitation events with no doubt whatsoever,” Kevin Trenberth of the US National Center for Atmospheric Research told a meeting in January. “Yes, all events. Even if temperatures or sea surface temperatures are below normal, they are still higher than they would have been, and so too is the atmospheric water vapour amount and thus the moisture available for storms.”

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