Climate change primarily caused by burning fossil fuels, chopping down forestland and farming livestock has played an overwhelming role in the extreme heat waves blasting three continents this month.
"Without human induced climate change these heat events would however have been extremely rare," the World Weather Attribution initiative between scientists in Europe, the U.S. and India said on Tuesday.
British and Dutch climate scientists founded WWA in 2014 to examine how much climate change fuels extreme weather or climate-related events.
It includes scientists from institutions in France, India, the Netherlands, Switzerland, United States and United Kingdom, along with climate impact specialists at the Red Cross Red Crescent Climate Center.
Large areas of the U.S. and Mexico, Southern Europe and China experienced extreme heat and broke local high temperature records this month. In Eastern California's Death Valley and Northwest China temperatures exceeded 50° Celsius.
There have been heat-related deaths in the U.S. and Mexico, and in Spain, Italy, Greece, Cyprus, and Algeria, and in China. Millions of people in the U.S. and in Italy and Spain have been living under heat alerts.
More common and longer lasting
Conducted by a group led by Friederike Otto, a climate scientist at Imperial College London, the study used published peer-reviewed methods to analyze how human-induced climate change altered the likelihood and intensity of average maximum temperatures over some affected regions.
It found heat waves are amongst the deadliest natural hazards, yet global mortality figures are likely underestimated. "North America, Europe and China have experienced heat waves increasingly frequently over the last years as a result of warming caused by human activities," the scientists said.
As a result, heat waves can be expected about once every 15 years in the U.S. and Mexico, once a decade in Southern Europe, and once every 5 years in China, according to the scientists' computer modeling and weather observations.
The study found the heat-trapping carbon dioxide, methane and other gases in the atmosphere added 2° to the heat wave in the U.S. and Mexico, 2.5° to the one in Europe and 1° to the one in China.
The world has warmed by about 1.2° since the industrial era began, but the heat this month is likely the hottest that Earth has been in 120,000 years.
"Unless the world rapidly stops burning fossil fuels, these events will become even more common and the world will experience heat waves that are even hotter and longer lasting," the scientists concluded.
"A heat wave like the recent ones would occur every 2-5 years in a world that is 2° warmer than the pre-industrial climate."
