http://www.guardian.co.uk/uk/2013/jun/18/climate-uk-weather-summe...

http://www.guardian.co.uk/uk/2013/jun/18/climate-uk-weather-summer-rain
"Met Office meeting: UK's spell of awful summers is set to continue

Forecast that Britain could be in middle of 10-20 year 'cycle' of wet summers delivered following gathering at Met Office
Don't worry, summer is on its way – but you might have to wait until 2023.

As the prospect of another gloomy Glastonbury and wet Wimbledon looms, leading climate scientists have warned that the UK could be set for a further five to 10 years of washout summers.

The grim conclusion was delivered after an unprecedented gathering of scientists and meteorologists at the Met Office in Exeter to debate the range of possible causes for Europe's "unusual seasonal weather" over recent years, a sequence that has lasted since 2007.

Many will have hoped for news of sunnier times ahead. But after experts brainstormed through the day they delivered the shock finding that the UK could be in the middle of a 10-20 year "cycle" of wet summers. The last six out of seven summers in the UK have seen below-average temperatures and sunshine, and above-average rainfall.

Stephen Belcher, head of the Met Office Hadley Centre and professor of meteorology at the University of Reading, stressed that the finding was not an official long-term forecast and does not automatically mean the UK will now have a further decade of wet summers. But, he said, the scientists' conclusion was that the chances of this occurring are now higher than they first thought.

"Predicting when this cycle will end is hard," said Belcher, who led the meeting of 25 scientists. "We have seen similar patterns before – in the 1950s and the 1880s – and we have hints that we are coming towards the end of this current cycle. However, it might continue for the next five to 10 years. There is a higher probability of wet summers continuing. But it's very early days in trying to understand why this is happening."

The scientists must now address what "dynamical drivers" are causing this cycle, Belcher said. The meeting debated a range of possible interconnected reasons for the unusual weather of recent years, including this year's cold spring and the freezing winter of 2010/11. The most likely cause for the wet summers, he said, was the Atlantic multi-decadal oscillation, or AMO, a natural pattern of long-term changes to ocean currents.

Other candidate causes that could be "loading the dice", as Belcher described it, include a shift in the jet stream, solar variability and fast-retreating Arctic sea ice. Aggravating all of these factors could be the influence of anthropogenic greenhouse gases entering the atmosphere.

Dr James Screen, who studies how melting sea ice impacts on the jet stream at 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."

The scientists also debated how melting sea ice should be better incorporated into climate models, as well as how observational data – for example, deep-ocean temperatures – could be improved to help their understanding of the potential relationship between climate change and the recent run of inclement weather and record-breaking extremes.

Len Shaffrey, a climate modeller based at the University of Reading who is also currently investigating possible links between Arctic sea ice retreat and European weather, said: "There are some fascinating science questions emerging about the influences on our weather, for example, from natural variations in ocean temperature. There is also some evidence that the record low amounts of Arctic sea ice have influenced patterns of European and British weather, but this evidence is not yet conclusive either way."

The scientific debate about the role of the jet stream – the fast "river" of meandering, 10km-high air which greatly determines UK weather - is intensifying. This week researchers from the University of Sheffield published a study in the International Journal of Climatology showing how "unusual changes" to the jet stream caused the "exceptional" melting of the Greenland ice sheet during the summer of 2012. Scientists say they must now determine what is causing these "displacements", as they are known, in the jet stream.

Tourist bosses were trying to find silver linings. David Leslie, a spokesman for the tourism agency Visit Britain, said people did not come to the UK for the weather alone. "The weather here is as unpredictable as anywhere else," he added.

"The days of the UK being seen as a foggy, wet destination have passed. Hot, cold or mildly pleasant, the weather is not a deterrent for overseas visitors coming here to enjoy Britain's tourism offering, which remains the best in the world."
and
http://www.bbc.co.uk/blogs/paulhudson/posts/Have-weather-patterns-really-been-unusual
"Thursday 20 June 2013, 17:31

Paul Hudson
The Independent headline was similar to others in the media, advising readers to ‘Stand by for another decade of wet summers’, continuing that the UK was in the midst of a ‘rare’ weather cycle.

This cycle, scientists announced, was the Atlantic Multidecadal Oscillation (AMO).
But as it turns out, there’s nothing rare or unusual about it at all.

The AMO was first identified by researchers nearly 20 years ago, incidentally when I had just begun my career as a forecaster at the Met Office, and describes a natural, cyclical warming and cooling of the North Atlantic Ocean over time.

This cycle is known to affect temperatures and rainfall, and alter North American and European summer climate.
In the UK, it leads to an increased risk of summers that are wetter than average.
It’s also linked with changes in the frequency of Atlantic Hurricanes, and of North American droughts.
The 1930’s and 1950’s in North America are dominated by heat records and correlate almost perfectly with a warm AMO.
The AMO has a cycle of approximately 70 years and would mean the current warm AMO is likely to last into the next decade.
But talk of another decade of wet summers is misleading.
If as expected the warm AMO continues then there’s a higher risk of wet summers – but it certainly doesn’t mean every summer will be a washout.

It’s worth remembering that one of the warmest, sunniest summers on record happened in 1959 – during the previous warm AMO cycle.

The return to much colder winters discussed at the conference has coincided with another natural phenomena – that of low solar activity - which has been shown to be associated with weather patterns that encourage cold winters across the UK and Europe.

It goes to show that at a time when it seems that every weather event or climate pattern is linked in some way to man-made climate change, natural weather cycles like the AMO can offer a more straightforward, natural, explanation.
"
AMO or abnormal events, there will be more cloud cover! therefore less PV and a boost for Wind and CHP.
Cheers