Since the 1980s, the number of people in urban areas exposed to extreme heat events has skyrocketed, tripling between 1983 and 2016.
Scientists warned in a new study published Monday that urban population growth paired with warmer temperatures due to climate change have contributed to increasing numbers of people experiencing extreme heat, the number one weather-related cause of death in the U.S.
The researchers wrote in the Proceedings of the National Academy of Sciences that the problem of urban heat is even worse than we thought because earlier studies underestimated extreme heat exposure, particularly in areas experiencing rapid population growth.
Using thermal infrared satellite data combined with daily temperature measurements on the ground, the researchers identified extreme heat events — meaning a wet-bulb temperature of 86 degrees Fahrenheit or more — in 13,115 cities around the world. The scientists then counted “person-days” of heat, meaning the number of days of extreme heat multiplied by the number of people in cities who experienced it. While 1983 saw 40 billion person-days of heat per year, 2016 had 119 billion, a 200 percent increase.
The researchers also found that in 2016, 1.7 billion people, making up 23 percent of the global population, had seen higher levels of urban heat exposure that year. They attributed one-third of the increase in heat exposure to increased temperatures caused by climate change, but most of the growth is because more people are moving to urban areas.
Heat in cities is particularly dangerous because of the heat island effect, where pavement, buildings, and other infrastructure absorb and emit heat from the sun. Lack of greenery in cities contributes to this effect. In the wake of a deadly, historic heat wave this summer in the Pacific Northwest, the White House in September launched an all-of-government effort to reduce the number of deaths from extreme heat. Six federal agencies will collaborate to protect workers, children, seniors, and at-risk communities.
While there are solutions for urban heat — such as building green roofs and planting trees and vegetation — the problem of global warming will only continue to get worse unless we take drastic action to cut global carbon emissions that cause rising temperatures. A recent climate report from the United Nations, which the U.N. secretary-general called a “code red for humanity,” warned that extreme heat events that once happened every 50 years are five times more common at current warming levels. And as warming levels rise, so will the frequency of deadly extreme heat events.