A blistering and unseasonable heatwave has struck southern Spain, Portugal and Morocco this week, with temperatures approaching 40°C (104°F) in some regions. The hot weather has heaped further climatic stress on southern Europe, which is already under a severe drought that is threatening to push up food prices. Here is what we know about why the record-breaking heat is occurring, and how it could be linked to climate change.
Which countries have seen records broken?
On 27 April, Spain recorded its hottest-ever April temperature at Cordoba airport in southern Spain, which reached 38.8°C (101.8°F) according to the Spanish meteorological service. This smashed the previous record of 37.4°C (99.3°F), set in April 2011 in Murcia.
Portugal also recorded its highest ever April temperature of 36.9°C (98.4°F) at Mora, in the centre of the country, on the same day, while in Marrakech, Morocco, temperatures reached a record 41.3°C (106°F).
These temperatures are 10 to 15°C above the seasonal average, according to the UK Met Office.
Why is this happening?
The heatwave is being driven by a mass of very hot air travelling from north Africa into southern Europe, coupled with a slow-moving high pressure system that is suppressing rainfall and keeping skies clear, allowing heat to build.
The ongoing drought in these countries is likely to be also playing a part. Moist soils provide a cooling effect as the water they contain evaporates. If soils are dry, little of the sun’s energy is used for evaporation and transpiration, leaving more solar radiation to accumulate as surface warming.
Erich Fischer at ETH Zurich in Switzerland says dry soils can increase the severity of a heatwave by 2 to 3°C. “Drought is basically an amplifier of the heatwave,” he says. But, he notes, it is unusual to see this effect so early in the year. “Typically at this time of year, even in southern Europe, the soils still have humidity,” he says.
What is the influence of climate change?
Any heatwave today is made more severe because of the background rate of warming under climate change, says Fischer. But the sheer volume of record-breaking severe heat events seen in recent years should cause alarm. Indeed, southern Europe and north Africa aren’t the only parts of the world experiencing extreme heat right now. South-East Asia has also been hit by extreme heat in recent weeks, with record temperatures of up to 45°C (113°F) recorded at monitoring stations across Thailand, Laos, Myanmar and Vietnam earlier this month. “Records should be very rare these days,” says Fischer. “But they are occurring all over the place.”
There is some emerging evidence that suggests cold sea surface temperatures in the North Atlantic Ocean may influence the occurrence of extreme heat in Europe, by influencing the movement of the jet stream and ocean currents.
Does this mean summer will be hot as well?
The current heatwave gives meteorologists little indication about what will happen during the northern hemisphere summer months. However, if the drought persists, Europe and north Africa could be more susceptible to extreme heat if a high pressure system hits later this year. “It is too early to say what these spring extreme temperatures will mean for the values in summer,” Paul Hutcheon at the Met Office Global Guidance Unit said in a blog post earlier this week. “But the dry ground will mean that further heatwave conditions have the potential to lead to even higher temperatures later in the year.”
Why is it still cold in the UK and northern Europe?
In contrast to the sweltering temperatures of southern Europe, much of northern and eastern Europe – including the UK – have been facing below average temperatures this week.
While a jet stream wave is bringing warm air over south-west Europe, cold air is being pulled down from the Arctic over the UK and northern Europe. But forecasters expect the cold snap to end within the next few days, bringing temperatures back closer to average across much of the UK by next week.