Is climate change to blame for Cumbria floods?

Alok Jha

Former Science Correspondent

A man by Pooley Bridge in Ullswater, Cumbria surveys the damage after it collapsed following heavy flooding. Credit: Press Association

Flooding is the biggest threat that the UK faces as a result of climate change. Across the world, some places will get warmer, others cooler, some will get drier and the UK will almost definitely get wetter - especially during winter.

But I don't need to tell you that, you can see it yourself not only in the devastating floods in Cumbria these past few days but also in the increasingly frequent and shocking flood events happening across the country in recent years.

The UK government's first comprehensive climate change risk assessment in 2012 identified that up to 3.6 million people would be at risk from floods by 2050, with financial damage increasing to £2bn-£10bn by 2080.

The basic physics of why a warmer world means more floods is well-established: as temperatures rise, the air gets warmer and is able to hold more moisture. Warm, moist air is the basic material for a rainstorm, which means climate change is slowly increasing the likelihood of storms, while also making each of those storms more powerful.

A hurricane that forms out in the ocean and blows into a coastal town in the UK not only brings with it more rain than ever in a warming world, the increased sea level around our coasts (another result of rising global temperatures) means that storm surges there will be worse and more likely to overwhelm flood defences.

Somerset was hit by devastating floods in 2014. Credit: PA

But how do we know whether an extreme event such as the Cumbrian floods is the result of climate change, rather than the normal variability of the UK's chaotic weather system?

Any responsible climate scientist will tell you that it isn't possible to definitively link individual events - storms or heatwaves or whatever else - to global average changes in climate.

However, things aren't so cut and dried. In recent years, scientists have begun to model the climate in such a way that they can begin to tease out how likely a certain event is to have been influenced by human-caused climate change, as opposed to other natural variations such as El Nino.

One of the first times scientists tried this out was in 2003, in which they showed that climate change had doubled the chances of the extreme heatwave seen in Europe that year.

A decade later, scientists at the University of Oxford worked out that the floods in Somerset and Cornwall in 2013/14 had links to climate change - the probability of seeing an event like that was 25% higher now than before humans began to interfere with the climate.

One of the UK's leading scientists looking at these types of attribution studies is Professor Peter Stott of the Met Office and he previously discussed some of his techniques in relation to the 2013/14 floods.

High levels of rainfall were seen in December 2013 and January 2014. Credit: Met Office

So far, there has not yet been enough time to study in sufficient scientific detail whether or not climate change was the main factor in causing the Cumbrian floods. But in the many conversations I've had with scientists and others in the past few days, there seems to be a growing consensus (albeit informal) that there is indeed a link.

Even the Met Office, the most cautious of scientific bodies, pointed me towards a paper they had published in November, which showed that under equivalent weather patterns to Cumbria, "extreme rainfall over 10 consecutive winter days is now seven times more likely than in a world without human emissions of greenhouse gases".

The worrying part of all this is that, as the world warms, there is the real possibility that the scenes we saw over the weekend in Cumbria might not seem that extreme in future.

Professor Gail Whiteman of Lancaster University, who is currently attending the United Nations' COP21 climate talks in Paris, said that the Cumbrian floods had been a big topic of conversation among delegates there. Even Al Gore mentioned it to delegates during a speech on Tuesday.

The United Nations' COP21 climate talks have been taking place in Paris. Credit: Reuters

Professor Whiteman added that to view the recent events as "extreme" was short-sighted.

"Thanks to climate change, extreme weather is the new normal," she said. “Unless serious commitments are made here in Paris, extreme weather will increase with global warming and thus climate adaptation measures, like flood defences, need to constantly be updated.

"What may be appear to be sufficient to withstand a one in 100 years event can become quickly out of date as the incidence of extreme weather ramps up and becomes more unpredictable.”

It is perhaps a macabre irony that the latest, most devastating impact of climate change has come to the UK right in the middle of COP21, a vast summit in which world leaders are trying to reduce human damage to the environment. If anyone needed a wake-up call to care about what all those people are trying to achieve in Paris, this was it.