19 march 2013

Hurricanes as big as Katrina will become 10 TIMES more frequent with just two degrees of global warming, study warns

* Two degrees celsius warming is the 'safe limit' set by climate scientists
* Storms as severe as the 2005 cyclone could happen once every two years
* Katrina killed 1,836 and left millions homeless

By Damien Gayle, Mail Online, March 19, 2013

Storm surges as devastating as those caused by Hurricane Katrina could happen 10 times more often if global temperatures rise by just two degrees, new research warns.

An estimated 1,836 people lost their lives and millions more were left homeless by the cyclone, the worst to ever hit the U.S., after it submerged New Orleans and other Gulf of Mexico communities in 2005.

Much of the devastation was caused by storm surges whipped up by fierce winds, which saw sea levels rise by between 24 and 28 feet along a 20-mile stretch of the Mississippi coast.

Image images//import_fef50db159ef9bcda93a3ed17db3d83c_article-2295305-0315B0040000044D-783_634x431.jpg

Devastating: A Red Cross truck sits flooded with other vehicles in front of a hotel just off Interstate 10 in Pascagoula, Mississippi, as Hurricane Katrina battered the area in August 2005 [click to enlarge.]

A 27.8ft surge at Pass Christian, Mississippi was the highest recorded
in U.S. history.

The new research suggests that even moderate climate change is likely to make such extreme storm surges as much as 10 times more frequent than they are today.

Since 1923, there has been a Katrina-magnitude storm surge roughly every 20 years.

Researchers calculated that with less than half a degree Celsius of global warming, this frequency would double.

A 1C rise produces a three to four-fold rate increase and if temperatures rise by 2C - the 'safe' limit for temperature change set by climate experts - extreme storm surges will become 10 times more common.

'This means there will be a Katrina magnitude storm surge every other year,' said Danish climate scientist Dr Aslak Grinsted, from the University of Copenhagen, who led the research.

The study compared historical storm surges with a range of different climate model predictions, taking into account natural phenomena such as El Nino, which warms the eastern Pacific and affects global temperature.

'We find that 0.4 degrees Celsius warming of the climate corresponds to a doubling of the frequency of extreme storm surges like the one following Hurricane Katrina,' said Dr Grinsted.

'With the global warming we have had during the 20th century, we have already crossed the threshold where more than half of all "Katrinas" are due to global warming.

'If the temperature rises an additional degree, the frequency will increase three to four times and if the global climate becomes two degrees warmer, there will be about 10 times as many extreme storm surges.'

He added that under normal conditions sea levels around the world were expected to rise as a result of global warming, making storm surges even more extreme and destructive.

Findings were reported in the journal Proceedings of the National Academy of Sciences.

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