Climate change made the UK’s record December rainfall, which caused the devastating floods, 50-75% more likely, a preliminary scientific investigation has found.

“Greenhouse gas emissions are loading the weather dice towards these warmer, wetter winters,” said Friederike Otto, scientific coordinator of the climateprediction.net project, which harnessed the collective power of roughly 70,000 home computers to run thousands of climate models extremely quickly.

The results, which were analysed at the University of Oxford and the Royal Netherlands Meteorological Institute, showed natural variation was equally influential in stocking the storms with rain and hurling them at northern Britain.

“Chance still played a large role in December’s weather,” said Otto, pointing to an abnormally large difference in water temperature in the east and west Atlantic. She said the possible contribution of the massive Pacific El Niño was still uncertain.

Throughout the last month of 2015, a succession of brutal storms - Desmond, Eva and Frank - struck the UK. Farmland and towns in Cumbria, Lancashire, Yorkshire and Scotland were submerged in deadly and heartbreaking floods.

It was the wettest December since records began 105 years before. At the same time, the UK average temperature was 8C, 4.1C above normal. The previous warmest December was in 1934 and was 6C on average.

Some of the rainfall can be explained by what is known as the thermodynamic effect. Warm air can carry more water, which means precipitation events become larger and more frequent in a warmed climate. But this had only increased the risk of such a wet December by around 7%.

The study, which was released publicly before being submitted to a scientific journal, simulated a world in which the accumulation of greenhouse gases in the atmosphere had not occurred and found that in the real world Britain was 50-70% more likely to receive the catastrophic rainfall levels of last month.

Otto postulated that disturbances of atmospheric pressure systems, caused by warming, was responsible for much of the increased risk. But this analysis had not yet been conducted.

The Met Office’s Peter Stott, who was not involved in the study, said it added further credence to the long-held prediction that climate change would bring wetter conditions to some parts of the globe and could be seen as broadly indicative of the role of climate change in the December floods.



“That is robust,” he said. He said the use of home computers to simultaneously run thousands of experiments dramatically increased the turn around of research, but he cautioned they were not powerful enough to run the most up to date global climate models.

“I think the uncertainty is potentially larger than the 50-75% [indicated in the study],” he said. “We are looking at very extreme parts of the calculations and it’s hard to be precise when we are talking about rare events like this.”

Nick Reynard, lead natural hazard scientist at the Centre for Ecology and Hydrology, said the picture was further complicated trying to link increased rainfall to flooding.

He said rainfall was known to be generally increasing in the UK, but at the same time “there is little compelling evidence for any upward trend in long records of flood magnitude or frequency”. This counter-intuitive finding was due to the differing ways particular catchments respond to heavy rain; some are known to be highly resistant to large events.

The links between extreme weather and climate change are now widely reported in academic papers. So perhaps more remarkable than the findings themselves, is the speed at which scientists are able to draw links between events. In the past, this work has taken months, even years. Thursday’s preliminary study has been released before the waters have even receded and is one of the fastest such analyses ever conducted.

Scientists told the Age newspaper in Australia last year that they were trying to adapt their responses to events in order to fit with the media cycle. Stott said the inclination to release preliminary results was understandable.

“The media, and people generally, are asking these questions as the flooding is happening or in the immediate aftermath. But we shouldn’t forget that as we seek to have the right policies and advise government about how best to protect ourselves from flooding, for that we need a carefully considered scientific analysis. You’ve got to be careful of over-interpreting very rapid studies,” he said.

Richard Black, the director of the Energy and Climate Intelligence Unit thinktank said the emergence of attribution science - our ability to find the fingerprints of climate change in individual weather events - was “one of the most exciting developments in the climate change field”.

“Only a few years ago scientists had to make do with saying things like ’this or that weather event is consistent with what we’d expect’ - but now, increasingly, it’s possible to determine whether climate change is increasing the risks of particular weather events, and by how much,” he said.

“That in turn gives policymakers the economic rationale they need to justify emission reduction programmes, as well as increasing the chances of legal action in future if decision-makers don’t act on the science.”