Urban heat is getting more dangerous
Urban heat is more dangerous—and even deadly—than ever. That’s true for two reasons: Globally, more people are flocking to cities, and cities themselves are getting hotter due to the climate crisis.
Those are the findings of a new study, published in the Proceedings of the National Academy of Sciences on Monday. In it, researchers examined heat exposure in 13,115 global cities from 1983 to 2016. The findings are a warning to cities as the climate crisis turns up the heat even further.
To first determine how hot and humid these cities are getting, the researchers examined temperatures using a data set that combines infrared satellite imagery and readings from thousands of weather stations. That helped provide widespread coverage, including areas with more sparse on-the-ground sensors.
The authors specifically focused on how often cities reached “extreme heat,” defined as a wet-bulb temperature of at least 86 degrees Fahrenheit (30 degrees Celsius), which is roughly the equivalent of 106 degrees Fahrenheit on the so-called “real feel” heat index. At that reading, most healthy people find it hard to function outside for very long, and older and unhealthy people face conditions that could be deadly. Wet-bulb temperature is a complex metric that combines measurements of temperature, humidity, heat radiation, and wind to determine what conditions the human body can handle.
Then, to see how many people were exposed to this extreme heat, the authors paired their weather data with statistics on the cities’ populations over the same 33-year time span.
The findings show that the number of person-days (or number of days multiplied by instances of extreme heat) that city dwellers were exposed to dangerous heat went from 40 billion per year in 1983 to 119 billion in 2016, which represents a stunning threefold increase. The authors found that population growth was responsible for two-thirds of that increase and that global warming accounted for the remaining third, but those proportions varied widely from city to city. [Continue reading…]