By the end of May 2015, roads in New Delhi, India were melting — literally. The extreme temperatures, beyond 45°C, twisted the white lines drawn on the asphalt.
Hospitals had to deal with an influx of patients struck by heat stroke. Electrical distribution systems were failing, exhausted by the incessant demand from air conditioning units.
Think of climate change as a global temperature increase of 2°C? Professor Taha BMJ Ouarda thinks of it in terms of heat waves.
“The impacts on public health — mortality and morbidity — are going to be phenomenal,” says Mr. Ouarda, a climatologist from Quebec’s National Institute for Scientific Research (INRS) who has just published an article on heat waves in India.
Professor Ouarda’s analysis confirms that anthropogenic climate change doubled the risk of heat waves in several parts of India in the 20th century.and century.
Moreover, in his study published at the end of February in Scientific ReportsProfessor Ouarda and his colleagues estimate that more than 70% of Indian territory will be in the grip of “extreme” heat waves by the end of the current century.
Worsening extreme weather is a counter-intuitive aspect of climate change. From 1901 to 2015, India’s average temperature increased by “only” 0.85°C, but heat waves are nevertheless much more frequent and intense.
“The average alone is not enough to describe the dangers we face,” explains Professor Ouarda in a telephone interview. The average temperature rise “flattens the curve” of extremes, to recycle a covid expression.
Duration, an important variable
To characterize heat waves, the researchers used an index that combines several parameters — such as the duration of the wave and its intensity compared to the seasonal average — into a single number.
Duration is an important variable: heat waves wreak havoc when they stretch out over time. “A sick child could withstand three or four days of extreme heat, but maybe not ten days”, gives as an example Mr. Ouarda.
Similarly, heat waves are particularly deadly when the mercury drops little at night. This leaves no opportunity for the body to recover before facing another crushing day.
Humidity also multiplies the effects of extreme heat. When the air is humid, the body has more difficulty evacuating excess heat by sweating.
And the frequency of heat waves — just one in the summer, or six waves in close succession — also influences the body’s ability to withstand them.
At the other end of the line, Professor Ouarda fumes against climate inaction. Even if we stopped emitting greenhouse gases right away, he says, the climate would continue to warm for three centuries.
“But that, the politicians do not talk about it, he continues. Because politicians, they want to get elected for the next five years, they don’t care what’s going to happen in 300 years. »
At least 2,500 people ultimately lost their lives in the heat wave that hit India in 2015.