Flooded Britain: who's to blame?
The flash floods that engulfed parts of Britain recently have left more than physical devastation in their wake. Breaking the surface of the receding waters with an indignant splutter is a question, being asked with increasing frequency across the UK: is climate change to blame? Live Earth UK put that question to climate expert Dr Richard Betts, of the Met Office Hadley Centre, to find out exactly where we should be pointing our fingers. Here's what he had to say.
Two obvious questions about recent major flooding events across large parts of the UK are (1) is this climate change and (2) do we expect more of this in the future?
Answering the second question first, yes, we do expect an increase in flood risk as a result of climate change. On the whole, a warmer climate means more evaporation from the oceans and hence more water in the atmosphere. In addition, warmer climates experience more intense rainfall: hotter ground drives stronger convection and hence produces more intense thunderstorm-type rain.
However, having said that, the flood events sweeping the country at the moment are not associated with thunderstorms driven by hot weather. They are more to do with frontal rain and the paths of low-pressure systems currently being driven across the UK by the jet stream, which is further south than it would normally be. It is not possible to say whether this is a result of climate change: the position of the jet stream does vary naturally in response to changing patterns of ocean surface temperatures (such as El Nino and La Nina events, which are warm and cool events in the equatorial east Pacific), but climate change can also cause the position of atmospheric circulations – such as the jet stream – to shift. We don't yet know which is responsible in this case, so neither possibility can be ruled out.
Virtual Earth
Some important new work published in the journal Nature, by an international team including my colleague Dr Peter Stott, looks at the changes in average precipitation (rainfall and snowfall) over many years. Using computer models, they find that a "virtual Earth" featuring only natural climate variations, and no human-caused climate change, does not reproduce the increase in precipitation we have seen in our part of the world. The observed changes are only reproduced when human factors, such as increased greenhouse gases, are included. So, the upshot of this is that the long-term average increase in precipitation over many years does seem to be due to human influences on the climate. However, we don't yet know whether the recent short-term extreme event is part of this or not.
Incidentally, it is worth pointing out that our computer model of climate is essentially the same one that is used for the weather forecast, which accurately predicted the recent heavy rain. In other words, you can believe what the weatherman says!
Dr Richard Betts, the official scientific advisor for the Live Earth event in London, is head of the Climate Impacts research team at the Hadley Centre. A climate modeller for 15 years, he was a lead author on the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and the Millennium Ecosystem Assessment, the authors of which shared the Zayed Environment Prize with Kofi Annan, then Secretary-General of the United Nations.
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