Photo: Greg Baker Agence France-Presse
Heat waves are more frequent and more intense in China since 1970, and even more since 15 years.
The great plain of Northern China, which are home to some 400 million people, could become a furnace of unbearable during future heat waves if global warming continues at the current rate, warn researchers.
The rising temperatures associated with high humidity, aggravated by the system of irrigation on a large scale may impose on the inhabitants of this agricultural plain, a danger more important than anywhere else on the planet, say in a press release.
This plain is home to mega-cities like Beijing, but also tens of millions of farmers.
Even if the world manages to slow down the warming, heat waves in the region could, by the middle of the Twenty-first century, exceed the capacity of resistance of the human body, according to the study published this week in the journal Nature Communications.
“This place is going to become the worst of the heat waves and life-threatening,” said the senior author, Elfatih Eltahir, Massachusetts Institute of Technology.
Heat waves are more frequent and more intense in China since 1970, and even more since 15 years. And the temperature there has increased by almost two times higher than the global average, is a height of 1.35 °C since 1950.
But the resistance of the human body heat also depends on the humidity : to perspire, the air at the surface of the skin must be more humid than the ambient air. The more the difference is important, the more the body cools off quickly.
As well, as there are in period of cold, a temperature felt by combining actual temperature and wind speed, there is one, called ” wet bulb “, which takes into account the humidity of the air.
Experts estimate that a healthy adult could not survive outside a temperature “wet bulb ” of 35 °C for more than six hours. Beyond that, “the body will quickly overheat, causing the death,” explains Jeremy Pal, Seaver College of Science and Engineering of Los Angeles, who has worked with Eltahir in the past.
For example, with an air humidity of 55 %, it would take an actual temperature of 44.4 °C to achieve the 35 °C ” wet bulb “. But at 85% relative humidity, 37.8 °C in actual temperature is sufficient.
The researchers, using climate models to predict heat waves in China to study two scenarios : one where climate change continues at the current pace, the other where humanity reaches the limit to +3 °C compared to the preindustrial era (one degree more than the goal of the Paris Agreement on the climate).
In both cases, the irrigation system of the plain of North China adds half a degree further, they estimate.
“The irrigation aggravates the impact of climate change,” insists Eltahir. Without radical measures against the emission of CO2, “the plain of North China will probably experience heat waves are deadly, with temperatures” wet bulb “beyond the threshold of tolerance of chinese peasants,” he continued.