Sun, Aug 12, 2012 page9

• Melting ice poses global challenges

  Recent inclement weather around the globe may be a sign of things to come

  • By Fiona Harvey / The Guardian, LONDON
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  Seeing satellite pictures from Greenland last month, scientists from NASA at first could not believe what the data were telling them. About 97 percent of the Greenland ice sheet was melting. The rate was unprecedented, with the thaw more widespread than ever as unseasonally warm weather across the Arctic took effect.

  “It was so extraordinary that at first I questioned the result: was this real or was it due to a data error?” said Son Nghiem, one of the scientists responsible for the research at NASA’s Jet Propulsion Laboratory in Pasadena, California. In a normal summer, some melting is observed over about half the island’s surface area. The new data — from three satellites — raised serious concerns over the progress of global warming and the likely consequences.

  For scientists at the UK Met Office’s Hadley Research Centre in Exeter, southwest England, the question was not just how fast Greenland was melting, but something much trickier. They have been crunching through years of data from dozens of satellites, trying to establish whether the conditions in the Arctic circle are related to the record-breaking washout of a summer in the UK.

  

  Illustration: Tania Chou

  When it comes to global warming, we can forget the jolly predictions of TV host Jeremy Clarkson and his ilk of a Mediterranean climate in which we lounge among the olive groves of Yorkshire.

  “We will see lots more floods, droughts, such as we’ve had this year in the UK,” said Peter Stott, leader of the climate change monitoring and attribution team at the Met Office.

  “Climate change is not a nice slow progression where the global climate warms by a few degrees. It means a much greater variability, far more extremes of weather,” he added.

  A series of unusually wet and cold summers has afflicted the UK for several years. Five out of the past six years (2007 to 2012), have shown below-average sunshine from June to August. All have had above-average rainfall — in some cases more than 50 percent above the long-term average.

  “It is not just a perception — we have had a run of relatively poor summers,” Stott said.

  This year has been the worst. April was the wettest on record and so was the period from April to June. The sun was missing too — June was the second dullest ever recorded. Hopes that this month might be better were dashed when the first few days brought floods as far apart as Scotland and Somerset, forcing scores of people from their homes.

  Nor has the UK been alone in suffering disastrous weather. In the US, the eastern seaboard has been hit by heatwaves and storms but even worse has been the “dustbowl effect” in Texas and across much of the nation’s agricultural heartland. India’s monsoon failed to appear on schedule, leaving millions of farmers in the sub-continent facing destitution. Floods in Beijing, after the heaviest rainfall in 60 years, caused devastation to millions.

  A food crisis is now all but inevitable, according to the US secretary of agriculture. Emergency plans are being discussed in India, while in China the clear-up is accompanied by concerns that environmental degradation may be making the country’s problems worse.

  Attributing any single weather event, or short pattern of events, however extreme, to climate change is always tricky. Extreme weather events occur, in the scientists’ term, stochastically — they happen by themselves, unpredictably, owing to the natural variations of the weather.

  However, the science of climate change has progressed rapidly in recent years. Last month, the Met Office and the US National Oceans and Atmospheric Administration published a groundbreaking report that showed recent events could be attributed to human causes. Last year’s unseasonably warm November in the UK — the second hottest since records began in 1659 — was shown to be at least 60 times more likely to have happened because of climate change than because of natural variations in the earth’s weather systems.

  “We are much more confident about attributing [weather effects] to climate change. This is all adding up to a stronger picture of human influence on the climate,” Stott said.

  For the British Isles, the melting Arctic could hold the key to whether the weather is changing as a result of human activity. Recent poor summers have been strongly linked by scientists to a change in the usual position of the jet stream, a weather system that normally lies in high latitudes during the northern hemisphere summer.

  Earlier this year, two US scientists published a paper in the journal Geophysical Research Letters, suggesting that the meandering of the jet stream could be linked to the reduction in sea ice. Edward Hanna, reader in climate science at the University of Sheffield, who is taking part in similar research, explains: “The last six summers since 2007, while often rather cool and wet over the UK, have brought Greenland unusually high air pressure, mild southerly winds, record-breaking temperatures and melting of the land ice.”

  The link, he believes, is that Arctic sea-ice losses and the release of heat over the Arctic Ocean have tended to weaken the jet stream and make it more meandering. This has brought more low pressures over Britain, less stable conditions, more cloud cover and rain-bearing weather systems from the Atlantic.

  This year, the jet stream moved much more than usual, passing south of the UK. It also persisted in this position for an unusually long time. If this pushing of the jet stream southward is indeed linked to less sea ice over the Arctic circle, as Hanna suspects, then the signs are that we will see many more of these wet summers in future.

  Despite the recent advances in climate-change science, it is too early to say whether this is certain. Hanna warns: “Six years is a relatively short time, and there are quite a number of other factors — sea-surface temperatures, variations in the sun’s power and the partly random and chaotic nature of atmospheric circulation — that can affect jet stream patterns.”

  That means it could take several years — aided by the roomfuls of supercomputers at the Met Office — to come up with more sturdy evidence linking our poor summers with climate change. If the link is established, it could mean similarly dull and disappointing British summers for many years to come.

  However, one piece of the picture may be about to fade. The majority of the most valuable data we have amassed — including the images of Greenland’s surface melting — comes from between 20 and 30 satellites that are now under threat. Ageing satellites are being removed from orbit and not being replaced, while those that remain are at ever greater risk of buffeting from the debris that now litters space.”

  There is a severe danger of not being able to see so clearly [from space] in future with the fall-out of satellites, uncertain government funding and so on,” Kate Willett of the Hadley Centre said.

  Unless the satellite data continues to stream down, we will never know whether the UK is at risk of a new age of drizzly summers and dry winters, and drought alternating with flooding.

  Meanwhile in Greenland, inhabitants have been basking in an almost unheard-of heat, regularly topping 20oC, with a succession of dry sunny days dominating the weather over the past two months.

  “It’s been lovely here, much warmer than usual — we’ve really been enjoying a nice summer,” said Henrik Stendal from his offices in Nuuk, the capital.

  British staycationers can only shiver in envy.
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