Wildfires, drought and extreme heat have been the talk of the town and country across Europe this summer. Attention has now turned to Portugal and Spain, where temperatures at the weekend reached more than 46℃ in some parts of both countries – close to the all-time European record of 48℃, set in Greece in 1977. Records aside, the obvious question is what is causing the current Iberian heatwave and whether this might be a harbinger of the future.
A number of factors can be identified. These include unusually warm sea surface temperatures in the North Atlantic, a wandering jet stream and associated “blocking” pattern of high pressure, a very dry land surface, and climate change.
The anomalous size and position of warm water areas in the North Atlantic this summer have shifted the so-called “polar front” northwards. This is the point where warm air from the south meets cold polar air, and any movement in the front will affect the distribution of high and low atmospheric pressure right across the Atlantic. This in turn influences the flow of westerly winds across the Atlantic and over Western and Southern Europe, especially the thin and fast “jet stream” in the upper atmosphere.
This summer, an area of persistent high pressure or “blocking” has become established over Western Europe and the eastern parts of the Atlantic. Such blocking causes the jet stream to appear “lazy” and wander much further north and south than its average position.