Parts of New York City are already underwater as hurricane Sandy bears down on the US east coast, bringing intense winds, torrential rain and a dangerous storm surge.
Sandy is merging with a winter storm from the west and an Arctic weather system, to become a hybrid 鈥淔rankenstorm鈥. Its winds have strengthened, according to the US National Hurricane Center (NHC), . Tropical-storm-force winds extend 780 kilometres from the storm鈥檚 centre.
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According to the US National Oceanic and Atmospheric Administration鈥檚 (HRD), the . HRD ranks the destructive potential of hurricanes from 0 to 6. The winds are currently ranked at 2.4, but the storm surge and waves rank at 5.7. That is slightly worse than , which scored 5.6. The NHC warns that New York and Long Island could see a storm surge of up to 3.3 metres (see diagram).
Slo-mo storm
Sandy is expected to linger for days, thanks to 鈥blocking patterns鈥 that make weather systems move slowly. Climate change will create more such situations in future, says at the Massachusetts Institute of Technology. 鈥淲e expect that hurricanes may move more slowly in the future than they do now.鈥
Slow-moving hurricanes like Sandy damage coastal areas by dumping rain onto a small area, causing severe flooding. 鈥淭his shifts rainfall towards the coasts, and increases it at the same time,鈥 says Emanuel. Usually, storms move inland and weaken, and lose much of their water.
We don鈥檛 know whether hybrid storms like Sandy will become more or less common as the world warms, says Emanuel. 鈥淲e haven鈥檛 really done our homework on this sort of event.鈥
Emanuel says it鈥檚 pretty clear that Atlantic hurricanes are on the rise, though, driven in part by warming oceans, made warmer through greenhouse gas emissions. But we don鈥檛 know whether winter storms will become more or less common, he says.
In harm鈥檚 way
Winter storms are powered by strong temperature gradients, so they are more likely when the poles are much colder than the tropics. At ground level, the Arctic is warming faster than the tropics, so this gradient will weaken. But higher up in the atmosphere, the tropics are warming faster still so the gradient will strengthen. 鈥淪ome models show an increase in activity and others show a decrease,鈥 Emanuel says. 鈥淲e鈥檙e a bit at sea about this.鈥
The first priority should be the growing number of people threatened, says of Woods Hole Oceanographic Institution in Massachusetts. 鈥淲e鈥檝e put a lot of people and resources in harm鈥檚 way,鈥 he says. 鈥淲e鈥檝e built cities on the beach.鈥 Sea levels are rising, and that will mean higher storm surges.
鈥淥ur susceptibility to events like this is going up dramatically, independent of climate,鈥 agrees Emanuel. 鈥淓ven if the climate remained constant, we鈥檙e going to see a lot more damage.鈥
