UK's wet summers 'could last for 10 years'

Weather and climate experts from across the UK came together at the Met Office's HQ in Exeter on Tuesday 18 June to discuss the recent run of unusual seasons in Europe.

And, while it didn't rule out "decent summers", it is thought the UK could see its run of wet summers continue for around 10 years, thanks to a shift in the jet stream, possibly as a result of climate change.

A total of 25 delegates attended including representatives from the Universities of Exeter, Leeds, Oxford, Reading and Imperial College London, as well as the Met Office.

Up for discussion on Tuesday was the weather patterns and their potential causes in three recent seasons – the cold winter of 2010/11, the wet summer of 2012, and this year's cold spring.

Professor Stephen Belcher, Head of the Met Office Hadley Centre and chair of the meeting, said: "Ultimately what we've seen in each of these seasons is shifts in the position of the jet stream which impact our weather in certain ways at different times of year.

"The key question is what is causing the jet stream to shift in this way? There is some research to say some parts of the natural system load the dice to influence certain states of the jet stream, but this loading may be further amplified by climate change."

There are a number of possible factors which could be 'loading the dice', including declining Arctic sea ice, solar variability, long-term ocean cycles, and other long-term cycles of natural variability, according to the Met Office.

Five out of the last six UK summers have seen above average rainfall (2010 is the exception, with average rainfall) and the workshop heard new evidence from the University of Reading suggesting that long-term Atlantic currents may be playing an important role.

The Met Office said in a statement: "These are understood to operate on cycles of a decade or more, which suggests that we may see their influence on our summers for a few more years to come. While these influence the odds of wet summers, it doesn't rule out the possibility of decent summers over the next few years."

With regards to the cold winters, there is a wide range of drivers that could have an influence.

There is some initial evidence to suggest that changes in Arctic climate may also be making an impact.

Dr James Screen, from the University of Exeter, said: "There has been a lot of talk about declining Arctic sea ice playing a role in our weather patterns, but really that's just one aspect of changes in the Arctic climate – which has seen rapid warming compared to other parts of the world.

"Those changes mean there is less of a difference in temperature between the Arctic and tropics, which could impact the position of the jet stream."

Another driver of colder winter weather has already been identified and is known as Sudden Stratospheric Warmings (SSWs).

The Met Office says recent research in SSWs has seen them able to give good advice up to a month ahead on cold spells in recent seasons when they have been driven by this phenomenon.

Variations in UV output from the sun have been identified as one potential driver of SSWs, but there may be others.

Dr Belcher said the workshops and research work "will help us continue our work to push forward understanding in this area so we can give better forecasts and advice on longer timescales in the future".

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