Explained | How climate change drives heatwaves and wildfires in Europe

Europe is once again battling scorching temperatures this summer, with wildfires blazing across the continent from the Mediterranean to Spain. Here's how climate change drives these events.

Hotter, more frequent heatwaves

Climate change makes heatwaves hotter and more frequent. This is the case for most land regions, and has been confirmed by the United Nations' global panel of climate scientists, the Intergovernmental Panel on Climate Change (IPCC).

Greenhouse gas emissions from human activities have heated the planet by about 1.2 degrees Celsius since pre-industrial times. That warmer baseline means higher temperatures can be reached during extreme heat events.

Every heatwave being experienced today has been hotter and more frequent due to climate change, said Friederike Otto, a climate scientist at Imperial College London who co-leads the World Weather Attribution global research collaboration.

But other conditions affect heatwaves too. In Europe, atmospheric circulation is an important factor.

Fingerprints of climate change

To find out exactly how much climate change affected a specific heatwave, scientists conduct "attribution studies". Since 2004, more than 400 such studies have been done for extreme weather events, including heat, floods and drought - calculating how much of a role climate change played in each.

This involves simulating the modern climate hundreds of times and comparing it to simulations of a climate without human-caused greenhouse gas emissions.

For example, scientists with World Weather Attribution determined that a record-breaking heatwave 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 climate.

Heatwaves will still get worse

The global average temperature is around 1.2 C warmer than in pre-industrial times. That is already driving extreme heat events.

On average on land, heat extremes that would have happened once every 10 years without human influence on the climate are now three times more frequent, according to ETH Zurich climate scientist Sonia Seneviratne.

Temperatures will only stop rising if humans stop adding greenhouse gases to the atmosphere. Until then, heatwaves are set to worsen. A failure to tackle climate change would see heat extremes escalate even more dangerously.

Countries agreed under the global 2015 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 cut emissions fast enough to meet either goal.

A heatwave that occurred once per decade in the pre-industrial era would happen 4.1 times a decade at 1.5 C of warming, and 5.6 times at 2 C, the IPCC says.

Letting warming pass 1.5 C means that most years "will be affected by hot extremes in the future," Seneviratne said.

Climate change drives wildfires

Climate change increases hot and dry conditions that help fires spread faster, burn longer and rage more intensely.

In the Mediterranean, that has contributed to the fire season starting earlier and burning more land. Fires burning since mid-July on the island of Rhodes forced the evacuation of some 20,000 people as an inferno reached resorts and coastal villages on the island's southeast.

Hotter weather also saps moisture from vegetation, turning it into dry fuel that helps fires spread.

Hotter, drier conditions make fires far more dangerous, according to Copernicus senior scientist Mark Parrington.

Without human-induced climate change, the extreme weather experienced across the world this summer would have been extremely rare, according to a study by World Weather Attribution. The study found that human-induced climate change played an absolutely overwhelming role in the extreme heatwaves that swept across North America, Europe and China in July.

Climate change isn't the only factor in fires

Forest management and ignition sources are also important factors. In Europe, more than nine out of 10 fires are ignited by human activities, like arson, disposable barbeques, electricity lines, or littered glass, according to European Union data.

Countries, including Spain, face the challenge of shrinking populations in rural areas, as people move to cities, leaving smaller workforces to clear vegetation and avoid fuel for forest fires building up.

Some actions can help to limit severe blazes, such as setting controlled fires that mimic the low-intensity fires in natural ecosystem cycles, or introducing gaps within forests to stop blazes rapidly spreading over large areas.

But scientists concur that without steep cuts to the greenhouse gases causing climate change, heatwaves, wildfires, flooding and drought will significantly worsen.

When people look back on the current fire season in one or two decades, it will probably seem mild by comparison, said Victor Resco de Dios, professor of forest engineering at Spain's Lleida University.