5 september 2013

Looming ‘sea level crisis’ faces US east coast, study finds

By Pilita Clark, Environment Correspondent, Financial Times, September 5, 2013

Cities along the US east coast face a looming “sea level rise crisis” from a growing number of disasters as severe as hurricane Sandy, according to research on links between extreme weather and climate change.

Human-made global warming was a factor in at least six intense weather events last year, the study shows, from the superstorm that hit New York in October to the record melting of the Arctic and US heatwaves.

Climate change also had a role in Spain’s drought and torrential New Zealand rains, though natural weather variation was a leading culprit in each case, and no strong connection was found in other prominent 2012 weather events such as the US drought.

“We don’t have evidence that we are seeing things that could not have happened without natural weather variability doing its stuff,” said Peter Stott of the UK Met Office, one of the report’s editors. “But potentially climate change can in some cases add something on top.”

The study, which examines 12 unusually intense weather events, is the second in as many years led by a group of UK and US scientists at the forefront of a relatively new field of science aiming to pinpoint the impact of human-induced climate change on specific severe weather events.

Until recently, climate scientists have been happy to attribute global warming as the cause for big changes such as rising average global temperatures but have shied away from blaming it for a single flood, drought or storm.

The authors of the report, however, say their work shows it is possible to show how climate change can intensify or exacerbate such disasters.

In the case of superstorm Sandy the wind speeds were not that great but climate-related sea level rise helped aggravate the flooding and infrastructure damage expected to cost around $60bn to repair.

Higher sea levels, which scientists say are occurring as the oceans warm and ice caps melt, are likely to mean such damage occurs more often in future, the study says.

“Our future scenarios of Sandy-level return intervals are concerning, as they imply that events of less and less severity (from less powerful storms) will produce similar impacts,” says the report, which is published in the Bulletin of the American Meteorological Society.

“Coastal communities are facing a looming sea level rise crisis, one that will manifest itself as increased frequency of Sandy-like inundation disasters in the coming decades along the mid-Atlantic and elsewhere.”

In a similar vein, the 2012 spring and summer heatwaves in the US could be mainly explained by natural variability, the report found. But human-induced climate change was a factor in the intensity of the warmth and affected the likelihood of such heatwaves recurring.

High temperatures are now likely to occur four times as frequently because of human-induced climate change, said scientists at the National Oceanic and Atmospheric Administration who led the study with Mr Stott of the UK Met Office.

The report, which combines research from more than 70 scientists, does not always give a clear indication of precisely how climate change is affecting certain events.

The editors likened its findings to the impact of speeding on a car crash.

“Adding just a little bit of speed to your highway commute each month can substantially raise the odds that you’ll get hurt some day,” the report concludes.

“But if an accident does occur, the primary cause may not be your speed itself: it could be a wet road or a texting driver. Similarly, while climate models may indicate a human effect is causing increases in the chances of having extremely high precipitation in a region (much like speeding increases the chances of having an accident), natural variability can still be the primary factor in any individual extreme event.”

Just as it is hard to say how much of an impact driving speed has in an accident involving wet roads or texting drivers, “different analyses of the same meteorological event can reach somewhat different conclusions about the extent to which human influence has altered the likelihood and magnitude of the event”, it added.

Last year’s study of the impact of climate change on severe weather, also published in the BAMS, found global warming sharply increased the odds of unusually severe 2011 weather such as the Texas drought, but not the devastating Bangkok floods.

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