Extreme Heat Limits Outdoor Activities For One Third Of Human Population

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Scientists from the Nature Conservancy have published a study in the journal Environmental Research — Health that finds nearly a third of people alive today are unable to work outdoors safely in the higher temperatures prevalent in much of the world.

Rising temperatures, driven by the continued burning of fossil fuels, are making it difficult even for many young, healthy adults to do basic physical activities, such as housework or walking up stairs during daylight hours at the height of the summer, the report warns.

The study shows that the limitations are greater for elderly people, who have less ability to sweat and thus control their body temperatures. The research combines physiological studies of heat tolerance with seven decades of global and regional data on population, temperatures, and human development.

On average, people over 65 now experience about 900 hours each year when heat severely restricts safe outdoor activity, compared with 600 hours in 1950. That’s equivalent to more than a month of daytime hours during which such activity outdoors places increased stress on the human body.

The Poor Suffer Most

Economics are a factor. Those most affected live in poorer countries or regions, even though they are far less responsible for climate breakdown that results from the combustion of fossil fuels. In some tropical and subtropical regions, heat restricts outdoor activity for older adults for between one-quarter and one-third of the year.

The most severe challenges are found in southwest Asia — Bahrain, Qatar, Kuwait, the United Arab Emirates, Iraq, and Oman,; south Asia — Pakistan, Bangladesh, and India; and parts of west Africa — Mauritania, Mali, Burkina Faso, Senegal, Djibouti, and Niger.

Within countries, there are huge variations according to geography, income groups, and types of work. In India, limitations are most pronounced across the Indo-Gangetic Plain and eastern lowlands, and least evident in the Western Ghats and the Himalayan foothills.

In South America, people in the Amazon basin are far more vulnerable than in the Andean highlands. In many Gulf states, wealthy people can ease risks with air conditioning, while poorer migrant workers are exposed to dangerous levels of solar radiation on construction sites and while doing other outdoor jobs.

A Livable Climate

The study goes further than previous research on global heat risks by examining the social and physiological capacity to adapt to heat. The authors measure “liveability” in different temperatures in METs, units that are equivalent to the average energy expenditure of a human at rest.

According to The Guardian, a manageable temperature is one in which people below 65 can perform up to 3.3 METs of activity — sweeping a floor or walking at a moderate pace — for an extended period without heat stress. That means they can regulate their core body temperature at a steady state. By contrast, “unliveable limitations’” are found at hot locations during hours when human activity is restricted to 1.5 METs. Those are primarily sedentary activities such as lying down or sitting.

“Here, we focus on where climates are livable,” the researchers wrote. “For a climate to be truly livable, people need the freedom to engage in everyday physical activities that require an elevated heat production (>1.5 METs) without suffering ill effects from the heat.

“By contrast, when at rest in extreme heat, conditions may be so severe that they are unsurvivable after extended exposure, as they may cause a person’s core temperature to reach a critical level for heatstroke, even when at rest.

“We define livability as the maximum level of physical activity that can be sustained under a given set of ambient conditions without experiencing an unchecked rise in core temperature, otherwise known as ‘compensable heat stress.’ Unlike traditional heat stress metrics, [our method] offers a more nuanced assessment by integrating ambient climate conditions with physiological factors such as age and individual limits to sweating.”

“Hundreds of millions of people can no longer safely go about their daily lives outside during the hottest parts of the year,” said Luke Parsons, lead author of the paper. “And those people are overwhelmingly in countries that have contributed least to the problem. […]

“In the near term, investments in heat early warning systems, cooling infrastructure, and protections for older adults and outdoor workers in the most affected regions are urgent. However, these local investments are not substitutes for the fundamental need to limit global warming.”

Heat Wave In US

As if to drive home the message of this latest research, the US National Weather Service today is warning residents of western states — especially California — that extreme heat up to 30º F above normal is heading their way.

“Brutal heatwaves are not just a summertime concern anymore,” said Jennifer Francis, a climate scientist with the Woodwell Climate Research Center. “Record breaking March temperatures will stretch across the Southwest, South Central, and Southeast states this week.”

Nine states across the Great Plains and West had their warmest winter going back 131 years, and five more, including California, had their second mildest, according to the US National Centers for Environmental Information. Overall, the US had its second warmest winter season measured from December 1 to February 28, The Guardian reports.

The record breaking heat has other dramatic climate consequences. Daniel Swain, a climate scientist with the University of California Agriculture and Natural Resources said California depends on the snowpack in the mountains to act as a natural reservoir that stores water through winter and releases it gradually in the spring and summer.

Even when major storms delivered heavy snow, including a system linked to one of California’s deadliest avalanches that killed nine people, the accumulation quickly melted because of abnormally high temperatures that followed in the wake of those storms. That, in turn, will put further pressure on dwindling water supply in the Colorado River.

“This heat wave looks pretty extreme by March standards across large portions of the Southwest, and that is saying something given the winter we have just experienced,” Swain said. “It is a very big deal both in the shorter term and in the longer term.” This week, more than 300 high-temperature records could be matched or broken across the US.

The Coming Crisis

Rising gas prices may cause some Ford Stupid Duty and Cadillac Excrescence drivers to scale back the number of miles they drive temporarily. But once the fuel emergency is past, they will be only too happy to return to their profligate ways.

Research that alerts us to dangers ahead is useful, but unless humans alter their behavior, more research papers will pile up in scientific journals while the Earth continues to overheat. There is precious little reason for optimism at this moment in time.