Heat waves


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. Last year more than half a million hectares burned in the European Union, making it the bloc’s second-worst forest fire season on record after 2017. Hotter weather also saps moisture from vegetation, turning it into dry fuel that helps fires to spread.
A heat wave 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. Letting warming pass 1.5°C means that most years “will be affected by hot extremes in the future. Greenhouse gas emissions from human activities have heated the planet by about 1.2 Celsius since pre-industrial times. That warmer baseline means higher temperatures can be reached during extreme heat events.
Every heat wave that what we are experiencing has been made hotter and more frequent because of climate change. Europe is in the grip of a record-breaking heat wave and wildfires are raging across the Mediterranean. Here’s how climate change drives these events. Hotter, more frequent heat waves Climate change makes heat waves hotter and more frequent. This is the case for most land regions.
But other conditions affect heat waves too. In Europe, atmospheric circulation is an important factor.
A study in the journal Nature this month found that heat waves in Europe have increased three-to-four times faster than in other northern mid-latitudes such as the United States. The authors linked this to changes in the jet stream a fast west-to-east air current in the northern hemisphere. To find out exactly how much climate change affected a specific heat wave, 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 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 climate.
The global average temperature is around 1.2C 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. Temperatures will only cease rising if humans stop adding greenhouse gases to the atmosphere. Until then, heat waves 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. Countries such as Portugal and Greece experience fires most summers, and have infrastructure to try to manage them though both have received emergency EU help this summer. But hotter temperatures are also pushing wildfires into regions not used to them, and thus less prepared to cope.