Soaring sea surface temperatures in the north Atlantic and western Mediterranean are partly fuelling the current heatwave in Europe, scientists have warned.
The temperature of the North Atlantic began rising above historical averages in March, reaching 1.3°C higher than the 1982-2011 mean on July 13, according to data from Copernicus.
It comes as temperatures are forecast to reach at least 47°C this week on the Italian islands of Sicily and Sardinia, while wildfires in Greece continue to rage.
In a battle to preserve forests, industrial buildings and holiday homes, evacuations continued for a third day alongside a motorway connecting Athens to the southern city of Corinth.
The surging temperatures are the result of an anticyclone, or area of high air pressure, named Charon after the ferryman of the dead in Greek mythology.
The weather system pushed into the region from North Africa, following hot on the heels of Cerberus, another anticyclone that caused a heatwave in the same part of the continent last week.
“As always with extreme temperature events like heatwaves, there are a combination of factors, both long term and shorter term,” Julien Nicolas, scientist at the Copernicus Atmosphere Monitoring Service, told The National.
“With regard to the long term, we know the climate is warming.
“But as always with extreme events there are some atmospheric circulation events that can lead to extreme temperature. In this particular case there is an area of high pressure over the western Mediterranean.
“And you have wind patterns associated with this area of high pressure that brings hot air from the Sahara towards western Europe, so [it is a] combination of the shorter-term atmospheric circulation on top of a long-term warming trend.”
He said the soaring temperature of the north Atlantic, particularly along the coast of western Europe, as well as the western Mediterranean, is also contributing. Parts of the Mediterranean Sea are expected to reach more than 30°C, according to the World Meteorological Organisation.
“So if you combine all the factors, this is how we can reach these temperature extremes,” Mr Nicolas told The National.
Heatwaves in Europe - in pictures
Sea temperatures surged last month and have been rising since.
Mr Nicolas said their current level was "really unprecedented".
“We are seeing a record high sea surface temperature, in the north Atlantic as a whole, but particularly on the eastern side," he added.
"This is quite unusual. This is another factor that comes on top of the others that can explain why we are reaching such high temperatures.”
Experts say marine heatwaves can also affect the migration of species and draw invasive species into European waters with consequences for fisheries and local fauna.
Although the current heatwave is expected to recede soon, if sea surface temperatures remain high they could help fuel further heatwaves this summer.
Mr Nicolas said scientists were already predicting a hot year, possibly the hottest ever, due to the presence of the naturally occurring El Nino weather phenomenon.
But the current El Nino only started a few months ago and is still weak to moderate. It is not expected to peak until winter.
“These El Nino conditions push the global temperature higher as they have a warming effect," the climate expert said. "We were sort of prepared but we are seeing some things happening at an unprecedented rate."
Dangers of extreme heat
The extreme heat in the Northern Hemisphere is increasing the strain on healthcare systems, hitting those least able to manage its consequences hardest, the World Health Organisation said on Wednesday.
"Extreme heat puts increased pressure on health systems. Exposure to excessive heat has wide-ranging impacts on health, often amplifying existing conditions and resulting in premature death," the WHO's director general Dr Tedros Adhanom Ghebreyesus said.
Alessandro Miani, who heads the Italian Society of Environmental Doctors, warned that ageing populations in Italy and other countries in Europe's south were a concern during heatwaves, because deaths due to high temperatures most commonly affect people over 80.
Italy, meanwhile, has put 23 cities on red alert.
“The excessive heat together with humidity can make it difficult for sweat to evaporate, interfering with the body's ability to regulate its own temperature,” Mr Miani said.
The heat in Rome eased only slightly after a sweltering 43°C on Tuesday, while highs in Sicily and Sardinia reached 46°C. Parts of Spain were as high as 45°C on Wednesday.
Wildfires continued to burn for a third day west of the Greek capital Athens, with water planes resuming operations at first light and firefighters working throughout the night to keep flames from reaching coastal oil refineries.
Fanned by erratic winds, the fires have gutted dozens of homes, prompted hundreds of people to flee and blanketed the area in thick smoke. Temperatures could climb to 43°C on Thursday, forecasters said.
Greek firefighters said Romania, Slovakia and Poland would send 230 firefighters to help efforts.
The Greek government pleaded with the population to be careful to not spark new fires.
France said temperatures of up to 40°C were expected on Wednesday in parts of the country's south, including on the Mediterranean holiday island Corsica.
A high of 29.5°C was recorded in the French Alpine ski resort of Alpe d'Huez, with 40.6°C recorded in Verdun in the foothills of the Pyrenees, a record for the area.
In the Canary Islands, 400 firefighters battled a blaze that has ravaged 3,500 hectares of forest and forced 4,000 residents to leave their homes, with authorities warning people to wear face masks outside due to poor air quality.