A study published earlier this month warned that exposure to extreme heat has increased dramatically in growing cities.
The study published in the Proceedings of the National Academy of Sciences found that the number of "person-days" in which people in cities are exposed to extreme combinations of heat and humidity has tripled since the 1980s.
The increase was caused by climate change and the “urban heat island effect,” when cities replace natural land cover with dense surfaces that retain heat.
Cascade Tuholske, a postdoctoral researcher at Columbia University’s Earth Institute who is the lead author of the study, said in a statement that the increase in exposure has “broad effects.”
“It increases morbidity and mortality. It impacts people’s ability to work and results in lower economic output. It exacerbates pre-existing health conditions,” Tuholske said.
The authors examined fine-resolution and population data to measure heat exposure for 13,115 cities from 1983 to 2016. Globally, urban exposure to heat increased nearly 200 percent in that time frame, affecting over 1.7 billion people.
The number of person-days in which those in cities were exposed increased from 40 billion per year in 1983 to 119 billion in 2016, a three-fold increase.
Exposure trajectories increased for 46 percent of urban settlements, which in 2016 comprised 23 percent of the planet’s population.
The study suggested that previous research underestimated extreme heat exposure, “highlighting the urgency for targeted adaptations and early warning systems to reduce harm from urban extreme heat exposure.”