The weather that has brought drought and baking heat to much of Britain can be blamed on a block of high pressure air that has stubbornly refused to shift itself from the British Isles. Normally this block would have been restricted to the Azores and the mid-Atlantic, but it has spread to Britain. Wet winds have been deflected from the airspace above the nation, as a result, and farmers have been left to cope with dried-up rivers and parched soil – although forecasters warned on Saturday that the hot weather would disappear this week, bringing cooler conditions in its wake.
Nevertheless, there is no doubt the spring we have just experienced has been an intensely hot, dry one. Nor is it without precedent. Meteorologists have noted that there have been several springs like it in recent years. The question is: why?
Most scientists suspect that global warming, triggered by the unprecedented amounts of carbon dioxide that humans are pumping into the atmosphere, is to blame in some way, though unravelling its impact from the myriad other meteorological influences that shape the weather is tricky.
One suggestion is that the change in weather may be due to the shrinking of the sea ice cap in the Arctic. Ice cover there has been disappearing at a striking rate and is currently at its lowest recorded level for this time of year. Less and less solar radiation is being reflected back into space as a result, and the atmosphere heats up. But how such a phenomenon could affect the weather over Britain is unclear.
One proposal concerns jet streams. This fast-moving air is found at an altitude of about 10km (32,800ft)and steers storm systems, determining whether regions are battered by bad weather or are starved of rainfall. They could be affected by shrinking ice caps and rising air temperatures.
Meteorologist Tim Woollings, of Reading University, said: "Climate models are starting to show some agreement that jet streams will shift slight closer to the poles in response to increases in greenhouse gases."
Such a trend could bring more settled, dry hot weather systems to Britain, though predictions are unclear. "There is still considerable disagreement between different models," Woollings added. "The hot weather we had this year arose because the jet stream was deflected south. Last year, it occurred because the stream was deflected north. So it is still very difficult to predict what will happen."
However, Woollings was sure that climate change would continue to have an influence. "One thing we can say is that even if the statistics of weather regimes do not change, we may feel the impact of some of them more strongly.
"In particular, if the background temperature is a few degrees higher than it is now, settled weather regimes in the summer will lead to more intense heatwaves and droughts than they do now."
