Warming increases storm surges

Katrina-scale storm surges could become 10 times more frequent with just a 2°C rise in global temperatures, a study has found.

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

Hurricane Katrina was officially the most destructive storm ever to strike the US. An estimated 1,836 people lost their lives and millions more were left homeless by the cyclone which pounded New Orleans and other Gulf of Mexico communities in 2005.

Much of the devastation was caused by storm surges whipped up by the winds, which saw sea levels rise by between 7.3 and 8.5 metres along a 32-kilometre stretch of the Mississippi coast.

An 8.4-metre surge at Pass Christian, Mississippi, was the highest recorded in US history. The new research suggests that even moderate climate change is likely to make such extreme storm surges far more common than they are today. Since 1923, there has been a Katrina-magnitude storm surge roughly every 20 years. With less than half a degree Celsius of warming, this frequency could double, the study shows.

A 1°C rise produces a three- to four-fold rate increase and if temperatures rise by 2°C – the “safe” limit set by climate experts – extreme storm surges become 10 times more common.

“This means there will be a Katrina magnitude storm surge every other year,” said Danish climate scientist Aslak Grinsted, from the University of Copenhagen, who led the research reported in the journal Proceedings of the National Academy of Sciences.

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

“We find that 0.4°C warming of the climate corresponds to a doubling of the frequency of extreme storm surges like the one following Hurricane Katrina,” said 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.