Experts blow hot and cold about global heatwave
Scientists split over role of climate change in worldwide phenomenon
The role of climate change in the current global heatwaves has split some of the most eminent scientific advisers.
Differences emerged on Tuesday about whether decades of dire predictions on the impact of global warming are “coming true before our eyes”, or if the northern hemisphere is simply experiencing a particularly hot summer, albeit one with tragic consequences.
To one body of opinion, the sustained and searing temperatures currently hitting Britain, Africa, Canada and Japan cannot be a coincidence.
The heatwave of 1976 may have been a freak, experts said, but in that year the serious heat was confined mainly to the UK and Western Europe, whereas now it is happening all at once in a number of regions across the planet.The argument was summed up by Professor Peter Stott, who leads the British Met Office’s climate monitoring team.
“What we’ve seen this summer is repeated [dice] throws throwing up a six in different parts of the world,” he said.
“If you get a six over and over again you start to think ‘this is not normal, someone has given me a loaded dice’.”
He said climate change models had predicted an increased frequency of heatwaves and these models are being borne out this summer.
For other scientists, the impact of climate change on the 2018 heatwave is less clear.
Professor Brian Hoskins, who sits on the UK Committee on Climate Change and heads the Met Office’s peer review panel, said global warming was a factor but that the heatwaves would have been only marginally cooler without it.“When 1976 happened, clearly that was extreme and no one thought that was climate change,” he said. “It is likely that this is only one degree warmer than it would have been. We have seen sustained warm and dry patterns. What we don’t understand at the moment is whether climate change makes these patterns more likely.”
Data shows that global temperatures have risen globally about 1°C above pre-industrial levels, with greater increases in the Arctic.Meanwhile, figures from Nasa show that last month was tied as the third-warmest June in 138 years of modern record-keeping at 0.77°C above the 1951 to 1980 average, with only June 2015 and June 2016 warmer.Whatever the wider role of climate change, most scientists agree that this European summer’s fierce temperatures are due to a significant slowdown in the jet stream, the atmospheric winds that push weather systems around the world.In the case of Britain, it has allowed a bank of high pressure to build up from the west of the UK, causing temperatures of 33.3°C this week. The jet stream slows down when less warm water is drawn from equatorial regions.
Stott said: “It’s settled into a pattern here this summer, and what that means when it’s in this pattern, the Arctic temperatures are very much warmer, and temperatures are globally very much warmer, it’s fueling these heatwaves.”But he said the “jury is out” on the extent to which climate change is affecting the jet stream.
Hoskins agreed that the cause of the jet stream behaviour was not currently known. He pointed out that while the slowdown was causing extreme situations in certain regions, this risked distorting perception of the bigger picture.
“The whole northern hemisphere is not warm,” he said. “The average temperature is not out of step with recent years.”
However, he made it clear that if the world does not achieve the goals set out in the 2015 Paris Accord, which is to limit global warming to 1.5ºC above pre-industrial levels, the current pattern of hot summers will become “usual”.