According to a new study by the Columbia Climate School, exposure to deadly urban heat has tripled since the 1980s. The increase is the combined result of both rising global temperatures and booming urban population growth.
The study looked at more than 13,000 cities worldwide and found that incidents of extreme heat and humidity have increased dramatically. It defined extreme heat as 30 degrees Celsius on the wet-bulb temperature scale that takes into account the effect of high humidity. In 1983, there were 40 billion person-days under such conditions. By 2016, the number was 119 billion. More specifically, in 2016 1.7 billion people were subjected to such conditions on multiple days.
Sheer urban population growth accounted for two-thirds of the increase, while actual warming contributed a third. Over recent decades, hundreds of millions of people have moved from rural areas to cities, which now hold more than half the world’s population. And because of the urban heat island effect, temperatures in cities are generally higher than in the countryside.
In the United States, about 40 sizable cities have seen rapidly growing exposure to extreme heat, mainly clustered in Texas and the Gulf Coast. Globally, nearly a quarter of the world’s population is affected by the increased incidence of extreme temperatures.
A study last year showed that combinations of heat and humidity literally beyond the limits of outdoor human survival have been popping up around the world. A wet-bulb temperature reading of 30 – equivalent to 106 degrees Fahrenheit on the “real feel” heat index – is the point at which even most healthy people find it hard to function outside for long, and the unhealthy might become very ill or even die.
Photo, posted March 5, 2007, courtesy of Michael Phillips via Flickr.