A scorching and unusual heat wave hit southern Spain, Portugal and Morocco this week, with temperatures approaching 40°C (104°F) in some areas. The hot weather has increased climate pressure on southern Europe, which is already experiencing a severe drought that threatens to drive up food prices. Here’s what we know about why the record heat is happening and how it could be linked to climate change.
Which countries have seen records broken?
On April 27, Spain recorded its hottest April temperature on record at Cordoba airport in southern Spain, which reached 38.8°C (101.8°F) according to the Spanish meteorological service. This broke the previous record of 37.4°C (99.3°F), set in April 2011 in Murcia.
Portugal also recorded its highest temperature on record in April of 36.9C (98.4F) in Mora, in the center of the country, on the same day, while in Marrakech, Morocco, the temperatures hit a record high of 41.3°C (106°F).
These temperatures are 10 to 15°C higher than the seasonal average, according to the British Met Office.
Why does this happen?
The heat wave is driven by a mass of very hot air traveling from North Africa to southern Europe, coupled with a slow-moving high-pressure system that suppresses precipitation and keeps skies clear, allowing the heat to accumulate.
The ongoing drought in these countries is also likely to play a role. Wet floors provide a cooling effect because 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 heating.
Erich Fischer of ETH Zurich in Switzerland says dry soils can increase the severity of a heat wave by 2-3°C. “Drought is essentially a heat wave amplifier,” he says. But, he notes, it’s unusual to see this effect so early in the year. “Generally at this time of year, even in southern Europe, the grounds are still wet,” he says.
What is the influence of climate change?
Any heat wave today is made more severe due to the rate of background warming linked to climate change, Fischer says. But the sheer volume of record intense heat events seen in recent years should cause alarm. Indeed, southern Europe and North Africa are not the only regions of the world experiencing extreme heat at the moment. Southeast Asia has also been hit by extreme heat in recent weeks, with record high temperatures of up to 45C (113F) recorded at monitoring stations in Thailand, Laos, Myanmar and in Vietnam earlier this month. “Records should be very rare these days,” says Fischer. “But they happen everywhere.”
Some emerging evidence suggests that cold sea surface temperatures in the North Atlantic Ocean may influence the onset of extreme heat in Europe, by influencing the movement of the jet stream and ocean currents.
Does this mean summer will also be hot?
The current heat wave gives meteorologists little indication of 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 tell what these extreme spring temperatures will mean for values in the summer,” said Paul Hutcheon of the Met Office Global Guidance Unit in a blog post earlier this week. “But the dry ground means further heatwave conditions could bring even higher temperatures later in the year.”
Why is it still cold in the UK and Northern Europe?
Unlike the sweltering temperatures in southern Europe, much of northern and eastern Europe – including the UK – faced below average temperatures this week.
As a wave of jet stream brings warm air over southwestern Europe, cold air is drawn from the Arctic towards the UK and northern Europe. But forecasters expect the cold snap to end in the coming days, bringing temperatures closer to average across much of the UK by next week.