Is climate change whipping up a storm?

13 December 2007

Scientists have taken a fresh look at how our warming world could be hit by hurricanes. With these tropical storms mysteriously on the rise, does climate change mean there's more to come?Antenna gets swept up by the evidence...

This work was published in the journal Nature on 13 December 2007.

Image: Glenn/GISuser

Think hurricanes are becoming more common? Well, you're right. Over the past 30 years, hurricanes have been hitting the Atlantic more often - and they're getting more powerful too.
At the same time, rising greenhouse-gas levels mean ocean temperatures have been getting warmer. So it's not surprising that scientists have started to worry that the two things could be linked. With global temperatures continuing to rise, could there be more stormy weather to come?

In 2005 Hurricane Katrina flooded 80% of all the land in New Orleans.

Image: Tidewater Muse

Perhaps not. Now, scientists have created a new way to examine how rising sea temperatures are influencing hurricanes - and it's not all bad news.
The researchers have found that a warmer world won't necessarily mean more frequent and intense hurricanes overall - in fact, some areas should see fewer storms. But scientists do say that the northern hemisphere will be hit the hardest, with more hurricanes expected in the Atlantic.

Climate change shouldn't mean more hurricanes, but it will affect where they hit.

Image: iStockphoto/Klaas Lingbeek-van-Kranen

How did they make the predictions?
Scientist Gabriel Vecchi explains: 'Climate scientists can give us good predictions of how ocean temperatures will change if we keep emitting greenhouse gases at this rate. We used these predictions to work out what we can expect for hurricanes around the world.

Gabriel Vecchi led the research at the US National Oceanic and Atmospheric Administration.

Image: National Oceanic and Atmospheric Administration

'Warmer oceans influence hurricanes in two ways,' says Gabriel. 'A small area of warm water near the hurricane helps a cyclone form because the evaporating water fuels the growing storm. But warmer oceans over a wider area heat the atmosphere, and this warm air actually makes hurricanes less efficient.'
With this in mind, the researchers explored 22 of the world's most advanced computer climate models, to see how these two effects would balance out in future.
The result? Warming oceans don't necessarily mean more hurricanes, so long as the heat is evenly spread around the world. But hurricanes do become more frequent and intense in hotspots where the temperature's uneven.

This image shows how sea temperatures could influence hurricane intensity. Areas shown in shades of red are expected to see more hurricanes.

Image: National Oceanic and Atmospheric Administration/University of Miami

It's bad news for the UK, since the northern hemisphere is predicted to warm more quickly than average, meaning hurricanes could be in store.

Image: iStockphoto/Mike Bentley

Areas of rapid warming should expect more storms, while places that are taking longer to heat up should see fewer.
So are worries about climate change just a storm in a teacup?
Climate scientist Nathan Gillett says not. 'This work doesn't show that greenhouse gases aren't going to change hurricanes at all - some areas will see more hurricanes, and some will see fewer. But at least this work predicts that we shouldn't see a big increase in hurricanes everywhere, which will be good news if it holds true.'

Nathan is a lead author in the latest report from the Intergovernmental Panel on Climate Change, the largest international panel of experts making recommendations on our changing climate.

Image: University of East Anglia

So can the work help us prepare for the worst?
Gabriel says the model still has some gaps: 'Factors like wind speed need to be taken into account before we can predict hurricanes accurately. But at least this work shows us that it's not as simple as thinking that climate change means more hurricanes across the board - we're going to have to think about it in more detail than that.'

Hurricane scientists will also need to consider waves and wind before making full predictions.

Image: iStockphoto/Heiko Grossmann

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