UK wet summers down to Atlantic warming

Professor Stephen Belcher

The UK’s recent run of damp summers could be down to a cyclical warming of the Atlantic Ocean. That was the view of scientists and meteorologists who gathered at the Met Office to discuss the unusual weather patterns of recent years. They said that this 10 to 20 year pattern of Atlantic warming was shifting the jet stream, leading to washouts in six of the last seven summers. But they suggested that the pattern would change at some point in the next decade.

The researchers said the location of the fast moving winds of the jet stream was critical to the UK’s weather. When it becomes fixed in position south of the British Isles, low pressure systems can get stuck in the peaks and troughs that form along the edge of the stream, leading to the seemingly endless rainy days that have characterised our summers in recent years.

Even the buzz of the London Olympics could not disguise the washout that was last summer, the second wettest for the UK since records began. Prof Stephen Belcher from the Met Office Hadley Centre, who lead the discussions said that changes in the Atlantic Multidecadal Oscillation (AMO), as the ocean current is called, was one of the prime factors.

“It’s the pattern of warm and cold water, it’s the contrast of the warm and the cold, when that sits in the right place beneath the jet stream, it can kind of steer the jet stream and influence where it goes,” he said. “I’m excited about this work, it’s a new thing that we didn’t really know about.”

Basket cases

The scientists said that the AMO phenomenon had occurred in the 1880s, the 1950s and in the early 1960s. The most recent research was published last year by a team at Reading University.

Explaining the cold winters of 2010/11 and this past spring were more of a challenge, said the scientists. Dr James Screen from the University of Exeter said that a more complicated basket of factors was involved.

“The cycle we’ve been talking about in the north Atlantic seems to be more important for controlling summer weather in the UK, our current understanding of the role of Arctic sea ice is that it is more important in controlling winter weather.”

The researchers say that the glimmer of good news is that the AMO might change in five to 10 years, and warmer summers might return. However the winter was more difficult to predict said Prof Belcher.

“There are hints we are coming to the end of the cycle. With the cold winter weather, the loadings of the dice don’t seem to follow cycles,” he said.

As to the current summer season, according to Dr Adam Scaife from the Hadley Centre, you’d be wise to keep an umbrella handy.

“In 2012, like the previous few summers, we’ve had conditions in the northernmost Atlantic that were much warmer than normal.

“So that pre-conditioning was there this year and that shifts the odds slightly in favour of this summer being wetter than the historical average.”