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Extreme Heat days have tripled since the 1980s and more are to come

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By Amy Norton
HealthDay reporter

WEDNESDAY, Oct 13, 2021 (HealthDay News) – City dwellers around the globe sweat three times as many “extreme heat” days as their counterparts in the 1980s, according to a new study.

The study is the latest, showing the increasing exposure of humans to dangerously high temperatures. Experts said it took a closer look at what was happening than previous research – and it suggests exposure to extreme heat is more common than thought.

According to estimates by the researchers, 1.7 billion city dwellers – or almost a fifth of the earth – were exposed to an increasing number of extremely hot days between 1983 and 2016.

These are temperatures that increase the risk of heat illness even for healthy people when they work or play sports outdoors.

For those who live in hot cities, “it’s not news that it’s getting hot,” said lead investigator Cascade Tuholske, a researcher at Columbia University’s Earth Institute in New York City.

It’s not that urban areas are the only places it’s hot, said Tuholske, who was a graduate student at the University of California at Santa Barbara at the time of the study.

But cities are sizzling because of a combination of two factors: climate change and the so-called urban heat island effect. A lack of grass and trees and an abundance of concrete and asphalt as heat storage conspire here.

In addition, more and more people around the world were moving to urban centers – which, as Tuholske’s team found, was another reason for the increasing extreme heat in cities.

The results, which were recently published in the Proceedings of the National Academy of Sciences, are based on data from more than 13,000 cities worldwide. Researchers estimated that the population was exposed to extremely hot days – what was defined as a “wet bulb globe” temperature of 30 degrees Celsius (86 degrees Fahrenheit) or higher.

This is a measure that not only takes temperature, but also humidity, wind speed and cloud cover into account. It gives an idea of ​​the temperature that feels to people who are in the sun.

When the wet bulb temperature hits 30C, a healthy person would begin to experience heat stress after 30 minutes of work or exercise outdoors, according to the US National Weather Service.

“Not only older people are affected,” said Tuholske.

His team estimates that people in these urban areas experienced a 200 percent increase in exposure to extremely hot days during the study period. The effects were not uniform, however: 25 urban areas accounted for a quarter of the increase in extreme heat stress.

The first four were: Dhaka, Bangladesh; Delhi, India; Calcutta, India; and Bangkok, Thailand.

Still, the problem was widespread, with nearly half of urban areas experiencing increasing exposure to extreme heat from residents.

According to Dr. Mona Sarfaty, director of the Climate and Health Program at George Mason University in Fairfax, Virginia, the results underscore the importance of gathering more precise details about what city dwellers are actually experiencing.

Some innovative projects aim to do this, she said. In Miami, for example, researchers have equipped “citizen scientists” with heat sensors to track temperatures in everyday life. At one bus stop, Sarfaty found, the average temperature exceeded 100 degrees Fahrenheit.

While global warming needs to be addressed with sweeping changes – including less reliance on fossil fuels like oil and coal – local action is also important, both Sarfaty and Tuholske said.

Cities can create more “green spaces,” Sarfaty said, not only to provide shade but also to cool the air. Some cities like Phoenix apply special coatings to asphalt to lower the temperature of the paved surfaces.

Local health officials and employers can also do more to raise awareness, Sarfaty said. She referred to a recent study in Texas that found that a “heat stress awareness program” reduced heat-related illness in urban workers who worked outdoors.

“People don’t necessarily realize how quickly the heat can succumb,” Sarfaty said.

As with so many health conditions, Tuholske said low-income and marginalized people are among the most vulnerable because they often work outdoors and lack air conditioning and other ways to reduce their exposure to dangerous heat.

Of particular concern are the people who live in cities around the world that are simply not designed to feed the large populations they have today.

More information

The World Health Organization has more about climate change and health.

SOURCES: Cascade Tuholske, PhD, Postdoc, Earth Institute, Columbia University, New York City; Mona Sarfaty, MD, MPH, Director, Climate and Health Program, George Mason University, Fairfax, Virginia; Proceedings of the National Academy of Sciences, online, October 4, 2021


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