Exposure to the deadly heat of cities has tripled since the 1980s and now affects nearly a quarter of the world’s population, according to a study.
Scientists attribute the disturbing trend to the combination of rising temperatures and the growing number of people living in urban areas, and have warned of its potentially deadly impact.
Over the past decades, hundreds of millions of people have moved from rural areas to cities, which are now home to more than half of the world’s population. Between surfaces such as concrete and asphalt, which trap and concentrate heat, and little vegetation, temperatures are generally higher in urban areas.
“It has broad effects,” said Cascade Tuholske, lead author of the study published in the journal PNAS and postdoctoral researcher at the Earth Institute at Columbia University. âIt increases morbidity and mortality. It has an impact on the ability of people to work and leads to a decline in economic production. This worsens pre-existing health problems.
The study used infrared satellite images and daily maximum heat and humidity readings of more than 13,000 cities from 1983 to 2016 to determine the number of people exposed to days per year exceeding 30 Â° C (86 Â° F ) on the humid globe temperature scale (which takes into account the multiplier effect of high humidity) in an area. They matched the results with the populations of the cities during the same period.
The study found that the number of person-days (the cumulative population exposed to cumulative heat in any given year for a particular location) increased from 40 billion per year in 1983 to 119 billion in 2016, a multiplication by three. In 2016, 1.7 billion people were subjected to extreme heat conditions over several days.
Although it varies by city and region, scientists have attributed two-thirds of the overall increase in exposure to increasing urban populations and one-third to global warming.
The most affected city was Dhaka. Between 1983 and 2016, a period in which the city’s population grew dramatically, the capital of Bangladesh saw an increase of 575 million person-days of extreme heat. Other cities that have experienced rapid population growth include Shanghai and Guangzhou in China, Yangon in Myanmar, Bangkok in Thailand, and Dubai in the United Arab Emirates.
Cities where at least half of their heat exposure is caused by global warming are Baghdad in Iraq, Cairo in Egypt and Mumbai in India.
Of the cities surveyed, 17% experienced an additional month of extreme hot days during the period, which spanned just over three decades.
Tuholske said, âMany of these cities show the pattern of the evolution of human civilization over the past 15,000 years. The Nile, the Tigris-Euphrates, the Gangesâ¦ there is a pattern where we wanted to be. Now, these areas can become uninhabitable. Are people really going to want to live there?
Meanwhile, in the United States, around 40 major cities were quickly exposed to the heat, including Houston, Dallas-Fort Worth, San Antonio and Austin in Texas, Pensacola in Florida, Las Vegas in Nevada, Baton Rouge and Lake Charles. in Louisiana and Providence in Rhode Island.
The PNAS article is one of several recently published studies examining the impact of extreme heat.
A Brazilian study analyzing the impact of forest loss on human health found that by 2100, up to 12 million Brazilians could be at extreme risk of heat stress due to large-scale deforestation of Amazonia and climate change.
The research, published Friday in the journal Communications Earth & Environment, discovered that there was a deforestation threshold in the Amazon that could threaten human survival if exceeded.
During this time, a European study published on Monday predicts that the economic costs of heat waves could be nearly five-fold by 2060.
Scientists at the European Commission’s Joint Research Center and other institutions estimate that recent heat waves have caused an annual loss of 0.3 to 0.5% of European gross domestic product, losses which they say will increase regularly over the next 40 years.
By the 2060s, they predict that heat waves will increase at an annual average of 1.14% and that southern European countries will suffer the highest economic losses.