The number of people exposed to extreme temperatures around the world is skyrocketing

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• The number of people exposed to extreme temperatures in the world is exploding

Climate change and rural exodus have tripled the exposure of populations to temperatures dangerous to their health. More than a quarter of the world’s population is now affected.

More and more people around the world are exposed to dangerous heat waves . This is revealed by a publication of Columbia University’s Earth Institute uploaded on October 4, 2021 – the full study is available in the journal PNAS

In their study From 13,000 cities around the world, the authors took into account the number of people exposed and the number of days they are exposed, data they combine into a “person-day” index. They found that this index has tripled since the 1980s. It went from 40 billion “person-days” to 119 billion “person-days” in 2016. In 2016, 1.7 billion people in the world were exposed. at extreme temperatures several days a year. More than a quarter of the world’s population is therefore now affected.

and the rising temperatures it brings are one of them, of course. But it is not the only one. If many people are now exposed to dangerous heat waves, it is also very directly linked to the rural exodus. “ In recent decades, hundreds of millions of people have left the countryside for the cities. These are now home to more than half of the world’s population ”, underlines the article by Columbia University.

The city environment is much more conducive to the “heat island” effect: there are few plants that cool the air. air, buildings prevent it from circulating, and surface materials trap and retain a lot of heat. Result: it is much hotter in town than in its direct surroundings. “ The increase in the urban population is responsible for two thirds of the increase in the exposure of people to temperatures extremes , specifies Columbia University. Climate change contributes a third.

Which cities are the most affected?

The city where the The highest ‘person-day’ extreme temperature exposure index is Dhaka, Bangladesh. Even if temperatures have also increased in the capital, this ranking is mainly linked to the fact that its population has increased a lot (from 4 million in 1983 to 22 million today). Many more people are therefore now exposed to the heat waves suffered by the city’s population.

Cities such as Shanghai, Guangzhou, Bangkok, Dubai, Khartoum, Hanoi and various cities Pakistan, India and the Arabian Peninsula face similar problems. In other cities, the increase in the number of person-days exposed to extreme temperatures is much more directly linked to climate change, such as Baghdad, Cairo, Lagos, Mumbai and other major cities. India and Bangladesh.

In Europe, the population of cities having remained more stable, the increase in the number of person-days is closely linked to climate change. The team found that in 17% of European cities surveyed, the number of extremely hot days had increased by more than a month over the past 30 years. In the United States, Texas and the Gulf Coast are the most exposed. In sum, Columbia University points out, the study does not take into account the record heat waves that the regions of the northwestern United States and southern Canada suffered and which killed hundreds of people. Extreme temperatures are a real health risk

The fact that the number of people exposed to heat waves increases as much is problematic. “ This has a very broad impact , says lead author of the study, Cascade Tuholske, post-doctoral researcher at Columbia University’s Earth Institute. This increases morbidity and mortality. This has an impact on the ability of people to do their jobs, thereby reducing economic performance. It also tends to exacerbate pre-existing health issues

To assess the exposure of the world’s population to extreme temperatures, the researchers crossed infrared satellite images with readings from instruments positioned on the ground. This enabled them to determine the maximum daily temperatures and the humidity rate of more than 13,000 cities from 1983 to 2016. They used the WBGT index (Wet-bulb globe temperature) which takes into account in particular the effect of humidity on the feeling of heat by humans – when the air is very humid, the human body indeed cannot dissipate heat through sweating.

How to adapt cities to climate change

Their study highlights how crucial it is to adapt cities in order to soften the impact that climate change will have on them – even in the best case scenario. Develop green spaces and paint the houses white can significantly help refresh these areas.

White cities reflect the sun’s rays and store less heat. // Source: Fabrizio Ponchia / Pixabay

While asphalt does not reflects that 4% of the sun’s rays, meadows reflect 25% and white surfaces up to 90%, recalls the magazine Yale Environnement 360. “ The higher the albedo of buildings, the less heat they absorb. The city will therefore be cooler in the evening, and the buildings will need less air conditioning ”,

New York has already launched : the city has had over 850,000 square meters of roofs repainted in white since 2009. This option has been tested, on more or less large perimeters, in other places of the world in particular in Milan in Italy, in Melbourne and Sidney in Australia and in

.

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