The Hot Zone

Extreme precipitation events pinpointed to global warming

Posted by Alison Hawkes on February 17, 2011
Category : Climate Science and Scientists

Extreme precipitation events seem to be becoming more common in the Norther Hemisphere. But it’s been very hard for scientists to pinpoint a major weather event to global warming. Still, when a 100-year flood comes and then returns in a matter of a few years, it’s hard not to consider it a sign of a warming world.

Several papers published this week in the journal Nature demonstrate that such extreme precipitation events in specific localities is the result of climate change and not an overactive imagination. The scientists studied the actual, observable precipitation patterns in the 20th century and then compared them to climate model simulations and a splash of probability to discover a close, predictive match up.

They claim that their results provide “first formal identification of a human contribution to the observed intensification of extreme precipitation.” The scientists, led by Seung-Ki Min at the Climate Research Division from Environment Canada in Toronto, say that the global climate models may, in fact, be underestimating the amount of extreme weather events, “which implies that extreme precipitation events may strengthen more quickly in the future than projected and that they may have more severe impacts than estimated.”

In another study, this one led by Pardeep Pall at the University of Oxford, looked at a specific weather event: the 2000 floods in England and Wales, which occurred during the wettest autumn since 1766. About 10,000 properties were flooded over, causing evacuations, disruptions in rail service and power supplies, and an economic dent of about a £ 1 billion.

Oxford scientists used a climate model and simulated different scenarios of rainfall patterns based on greenhouse gas levels in the atmosphere. The results were fed into a model that simulated severe river runoff and found that in nine out of 10 cases, the model forecast an increased risk of floods when 20th century levels greenhouse gases were included. Specifically, the increase in risk for floods in the autumn of 2000 in England and Wales was more 20 percent, and in two out of three cases more than 90 percent.

The scientists conclude that human-caused greenhouse gas emissions contributed to the flood risk in England and Wales in 2000. With such techniques, scientists are coming closer to determining which weather events are nothing more than the result of statistical flukes, and which may seem like aberrant behavior but are really right in line with what we might expect from a warming world.

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