Katrina-like hurricanes could more than double this century

Katrina-like hurricanes could more than double this century

18 March 2013, by Tamera Jones

That's the conclusion an international team of researchers came to after analysing the relationship between global temperatures and hurricane surges along the southeastern US coast since 1923.

In a previous study published in the Proceedings of the National Academy of Sciences, the same researchers estimate that hurricanes similar in size to Katrina have been twice as frequent in warm years compared with cold years.

'We've demonstrated a greatly increased Atlantic hurricane surge threat in a warmer world. And we've probably crossed the threshold where Katrina-magnitude hurricane surges are more likely caused by global warming than not,' says Dr Aslak Grinsted of the University of Copenhagen, lead author of the study.

Until now, researchers have struggled to demonstrate a clear causal link between global warming and increased Atlantic hurricane activity. The authors argue that this is often because they were relying on biased cyclone records.

Extreme storm surges are one of the most damaging aspects of hurricanes. So, Grinsted and scientists from the University of Copenhagen, Beijing Normal University and NERC's National Oceanography Centre (UK) reasoned that tidal gauge records could be used to reveal the biggest storm surges.

They scrutinised data from six tidal gauges in the southeastern US coast, from Galveston, Texas in the west to Atlantic City, New Jersey in the north, dating back to the 1920s. They describe their approach in a second report, published in the Proceedings of the National Academy of Sciences.

This shows that the biggest storm surges are dominated by hurricanes that reached the land rather than winter storms. Not just that, but the biggest storm surges also inflict the most economic damage.

The advantage of the new approach is the way the researchers relate storm-surge data from tidal gauges directly to hurricanes.

'People have looked at storm-surge data before, but they've not combined them into a large-scale regional record and related them to climate change. They've tended to look at individual weather events or individual sites,' says Grinsted.

Previous studies have suggested a strong link between rising sea-surface temperatures and an increased risk of hurricanes. Others have suggested links between key climate events such as El Niño, tropical temperatures or droughts in the Sahel region of Africa.

But until now, we haven't known if the rising trend in the numbers of Atlantic tropical cyclones over the 20th century could simply be a result of improved detection.

Using their novel approach, Grinsted and his colleagues took ten competing ideas about possible causes of increased hurricane activity – such as El Niño, tropical temperatures or droughts in the Sahel region of Africa – out of the equation. They show that warmer temperatures bring a huge risk of Katrina-size hurricane surges.

'Scientists have been extremely careful about saying some event has a cause. But here, it's fair to say that warmer conditions make hurricanes more probable,' says Grinsted.