Along with temperatures topping 40 degrees Celsius (104 degrees Fahrenheit), wildfires are raging across southern Europe with evacuations in cities in Italy and Greece.
The oppressive heat is part of a global pattern of rising temperatures, attributed by scientists to human activity.
Climate change is making heat waves hotter and more frequent. This is the case for most terrestrial regions, and this has been confirmed by the UN’s World Group of Climatologists (IPCC).
Greenhouse gas emissions from human activities have warmed the planet by about 1.2 degrees Celsius since pre-industrial times. This warmer baseline means that higher temperatures can be reached during extreme heat events.
“Every heatwave we experience today has been made warmer and more frequent due to climate change,” said Friederike Otto, a climatologist at Imperial College London who also co-leads the World Weather Attribution research collaboration. .
But other conditions also affect heat waves. In Europe, atmospheric circulation is an important factor.
A study published this month in the journal Nature found that heat waves in Europe grew three to four times faster than in other mid-northern latitudes like the United States. The authors linked this to changes in the jet stream – a fast moving air current from west to east in the northern hemisphere.
To find out exactly how much climate change has affected a specific heat wave, scientists conduct “attribution studies”. Since 2004, more than 400 such studies have been carried out on extreme weather events, including heat, floods and drought, calculating the role climate change plays in each.
This involves simulating the modern climate hundreds of times and comparing it to simulations of a climate without anthropogenic greenhouse gas emissions.
For example, World Weather Attribution scientists determined that a record-breaking heat wave in Western Europe in June 2019 was 100 times more likely to occur now in France and the Netherlands than if humans had not changed the weather. climate.
Heat waves will get even worse
Global warming is already causing episodes of extreme heat.
“On average on earth, extreme heat events that would have occurred once every 10 years without human influence on the climate are now three times more frequent,” said Sonia Seneviratne, a climatologist at ETH Zurich.
Temperatures will only stop rising if humans stop adding greenhouse gases to the atmosphere. By then, the heat waves are expected to worsen. A failure to tackle climate change would lead to an even more dangerous escalation in extreme temperatures.
Countries agreed under the 2015 Global Paris Agreement to cut emissions fast enough to limit global warming to 2°C and aim for 1.5°C, to avoid its most dangerous impacts . Current policies would not reduce emissions fast enough to achieve either goal.
A heat wave that happened once a decade in the pre-industrial era would happen 4.1 times a decade at 1.5°C warming and 5.6 times at 2°C, according to the IPCC.
Letting warming pass 1.5C means most years “will be affected by extreme temperatures in the future”, Seneviratne said.
Climate change causes forest fires
Climate change is increasing hot, dry conditions that help fires spread faster, burn longer and rage more intensely.
In the Mediterranean, this has contributed to the fire season starting earlier and burning more land. Last year, more than half a million hectares burned across the European Union, making it the second worst wildfire season on record after 2017.
The warmer weather also saps moisture from vegetation, turning it into dry fuel that helps fires spread.
“The warmer and drier conditions right now, it just makes [fires] much more dangerous,” said Copernicus lead scientist Mark Parrington.
Countries like Portugal and Greece experience fires most summers and have infrastructure to try to manage them – although both received emergency aid from the EU this summer. But warmer temperatures are also pushing wildfires into regions that are not used to them, and therefore less prepared to deal with them.
Forest management and ignition sources are also important factors. In Europe, more than nine out of 10 fires are started by human activities, such as arson, disposable barbecues, power lines or broken glass, according to EU data. But the climate crisis usually creates conditions that greatly worsen the effects of these fires.
Countries including Spain are facing the challenge of dwindling populations in rural areas, as people move to cities, leaving a smaller workforce to clear vegetation and avoid the accumulation of “fuel” for forest fires.
Certain actions can help limit serious fires, such as starting controlled fires that mimic low-intensity fires in natural ecosystem cycles, or introducing holes in forests to prevent fires from spreading quickly over large areas. large areas.
But scientists agree that without significant reductions in the greenhouse gases that cause climate change, heat waves, wildfires, floods and drought will get significantly worse.
“When we think back to the current fire season a decade or two from now, it will probably look mild in comparison,” said Victor Resco de Dios, professor of forest engineering at Spain’s University of Lleida.