Gloomy outlook as we face 10 more wet summers
Published 19/06/2013 | 09:05
Britain faces ten more years of wet summers, after the Met Office revealed the country is in the midst of a rare weather cycle that increases the prospect of summer rain and could last for two decades.
Since the cycle began in 2007, six of the past seven summers have been wetter than average - with last summer seeing the heaviest rainfall in a century at almost double the seasonal average.
Although the cycle does not guarantee wet summers, it “loads the dice” in favour of increased rainfall each year, making wet summers more likely for the next five to ten years. The prediction is based on the last two times the cycle - known as Atlantic multi-decadal oscillation - occurred, in the 1950s and early 1960s and in the 1880s.
“This is a really new and exciting finding,” said Professor Stephen Belcher, head of the Met Office Hadley Centre, of the research by the University of Reading.
“Up to ten years from now the cycle could persist and therefore there is a higher possibility of wet summers,” he added.
Climate change may be intensifying the natural cycle and may prolong it, but it is too early to say for certain, Professor Belcher said.
“Now we are beginning to unpick and understand, we can design experiments to understand whether climate change is playing a role. It could be, we just don't know - but we now have a clear research path to investigate this,” he said.
The weather cycle is determined, in part, by the way the atmosphere and the North Atlantic Ocean exchange heat, which guides the jet stream.
“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,” said Professor Belcher.
Scientists are making much of the jet stream and how changes in these strong winds are affecting the weather.
They say the jet stream has generally been travelling much further south in recent years than is normal. The jet stream usually travels north of the UK over the summer, but has often blown to the south in recent years, allowing colder air to come in from the north that reduces temperatures and increases rainfall.
One theory is that the accelerating loss of Arctic ice has reduced the temperature difference between the North Pole and the warmer, mid latitude countries such as the UK.
This has weakened the jet stream, which travel from west to east at speeds of more than 200 miles an hour five to seven miles above the earth's surface, making it less powerful and more meandering - often in a southerly direction.
Since the Atlantic multi-decadal cycle began, three of the seven summers have seen the triple disappointment of having below average temperatures, below average sunshine and above average rainfall, the Met Office said.
The Met Office gave its qualified warning about the potentially wet summers ahead, following a meeting to discuss whether the unusual weather patterns seen in recent years were in part influenced by climate change.
It convened a group of 25 experts at its head office in Exeter from Universities including Exeter, Leeds, Oxford, Reading and Imperial College London.
In addition to discussing the recent wet summers, they also debated this year's spring - the coldest in 50 years and the freezing winter in 2010/2011 which included the UK's coldest December since records began in 1910 with heavy snowfall that caused travel chaos over Christmas.
The Met Office said “there is some evidence to suggest that changes in the Arctic climate may be making an impact” on winter temperatures.
Summing up, Professor Belcher said: “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.”
The meeting came after the National Farmers' Union reported that wheat harvests are likely to be around 30 per cent lower than last year as a result of the extreme weather over winter, making it the second below-average harvest in as many years.
Beekeepers have also reported that a third of honeybee colonies failed to survive the winter following last year's wash-out summer and continuing bad weather into 2013, exacerbated by the late arrival of spring.