Heat stress due to extreme wet heat episodes will affect between 500 million and 1.2 billion people per year by 2100. An interval that depends on the climate scenario chosen: compliance with the Paris Agreements or continuation of emissions at the current rate. The results were published in the journal Environmental Research Letters on March 5.
Currently, the average temperature on Earth has warmed by about 1 ° C compared to the pre-industrial period. Whatever we do, the thermal rise will continue for at least the next ten to twenty years. In fact, by this horizon, the trajectory has already begun with greenhouse effect gases (GHGs) emitted in recent decades. When we talk about actions to limit global warming, we are essentially talking about the second half of the century.
The danger of humid heat episodes
In a new study, researchers have assessed the proportion of the world’s population who are at risk of heat stress by the end of the century. And this, according to different scenarios of global warming. “When we consider the risks associated with a warmer planet, we must pay particular attention to the extremes of heat and humidity. Which are particularly dangerous for human health, “says Robert E. Kopp, one of the co-authors of the paper. Indeed, previous work of this type tended to take into account only the so-called sensitive temperature.
Everyone has already experienced the obvious discomfort that accompanies hot and humid periods (in the sense of the humidity of the air). Under these conditions, the ability of the body to cool itself through perspiration is greatly reduced. Also, its temperature rises and the metabolism is affected. A parameter often used to assess the degree of severity of heat is the temperature of the wet globe thermometer.
The latter takes into account temperature, humidity but also other variables that we will not discuss in this article. The higher its value, the more the discomfort and the health risks increase (heat stroke, malaise, hyperthermia, etc.). Episodes of humid heat, therefore, present themselves as a very direct threat to living things.
Up to 1.2 billion people affected each year
However, simulations carried out by scientists show that extremes of this type multiply rapidly with climate change. 500 million people would be affected each year in an optimistic scenario where warming is limited to 1.5 ° C. This figure rises to 800 million for an increase maintained at 2 ° C. Finally, if GHG emissions remain at the current rate, more than 1.2 billion people would find themselves exposed. In other words, more than 4 times the current value. Global warming would then have reached 3 ° C on average.
The affected areas are particularly concentrated in the tropical strip where the air is already naturally hot and humid. But more temperate areas like North America also experience such extremes. Developments in these regions are just as threatening. Take the case of New York. With a warmer 3 ° C climate, extreme wet heat episodes would occur almost 24 days a year. Figures which recall the urgency to act now to limit as much as possible the rise in temperatures in the second half of the century.