Analysis shows exposure to extreme heat triples since ’83
Cities’ growth mixes with higher temps
World leaders have committed to limiting Earth’s rising temperature to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial times. But what does that feel like? It’s difficult to convey, because you may not notice changes in average temperature. But you might notice when it’s extremely hot.
Columbia University’s climate school recently published a global data set with estimates of both population and temperature. The Associated Press analyzed the data from 1983 to 2016 and found that exposure to extreme heat has tripled, affecting about a quarter of the world’s population.
As the global average temperature rises, so do the hottest daily temperatures. And, in some places, the hottest days can be dangerous to human health, causing heat stress.
Heat stress can create health problems, like rashes, cramps and heat stroke. Other risk factors include humidity, wind speed and the amount of shade.
The heat index takes into account temperature and humidity to suggest what it feels like in the shade on a hot day. But even the heat index doesn’t tell you what it’s like to be working in the full sun on an extremely hot windless day.
Increasingly, climate scientists and meteorologists advocate for the use of a different metric for understanding extreme heat. It’s called wetbulb globe temperature and it takes into account temperature, humidity, wind speed, sun angle and cloud cover.
The new data set uses estimates of both population and wet-bulb globe temperature to better understand how many people are affected by dangerously hot temperatures.
When the wet-bulb globe temperature exceeds 30 degrees Celsius (86 degrees Fahrenheit), people are advised to take rests if they’re working outdoors.
Researchers averaged temperature data over 13,115 urban centers identified in a data set from the European Union.
Out of those urban centers around the world, nearly half experienced an increasing trend in heat exposure.
In 2016, just under 1.7 billion people lived in those areas, with the majority in Asia and sub-Saharan Africa.
The most affected region, by far, was southern Asia, where India alone accounted for 37% of the population living in areas with an extreme heat trend.
With population growth from 1983 to 2016 for each city and estimates for the year-to-year increase in annual counts of dangerously hot days, the AP identified the cities in the world where exposure to extreme heat is increasing most.
In Dhaka, Bangladesh, the population more than tripled from about 7.7 million in 1983 to 24 million in 2016. While the city grew by more than 16 million people, the number of extreme heat days also increased by 1.5 days a year, until Dhaka experienced about 50 more dangerously hot days a year than it did in 1983.
Population growth and increasing temperature both contribute to exposure trends. That was the case in Kolkata, India, the population grew by 6 million and the number of hot days grew by 1.76 each year. Meanwhile, New Delhi added nearly 14 million people. The city added 1.12 additional hot days each year.
Many cities that already experience extreme heat are growing rapidly.
Douala, Cameroon, grew from roughly 760,000 people in 1983 to nearly 3 million in 2016. United Nations population projections suggest that count will double by 2035. Douala’s citizens endured 76 days of extreme heat in 2016.