How Much Heat Can We Stand?

Today’s post is by John Balbus, M.D., the Chief Health Scientist at Environmental Defense.

“If you can’t stand the heat, get out of the kitchen.” That saying may work for part-time chefs, but it doesn’t do much for the victims of recent heat waves. They couldn’t escape the unusually severe temperatures.

A warmer world is likely to bring two different types of heat: warmer average temperatures, especially at night, and more frequent extremes. What do higher temperatures mean for us?

The human body is remarkably good at adapting to higher temperatures when the changes aren’t too sudden. This is why heat and humidity levels that would be harmful in Seattle are well-tolerated in Miami. As the average temperatures in places like Seattle or Boston rise slowly, we would expect residents to slowly accustom themselves to the change.

But short-lived extremes like heat waves are more worrisome. Studies done over the past few years suggest that bouts of extreme, unusual warm weather are especially lethal, particularly if they occur early in the season before people have a chance to acclimate to heat, or in places with few air conditioners.

Central air conditioning appears to make a big difference in easing the effects of sudden heat. Several studies have shown that access to central air conditioning greatly reduces deaths associated with heat waves. In Northern and Central Europe, where many buildings and even hospitals don’t have air conditioning, as many as 70,000 people died in a severe heat wave in 2003. This is also why heat waves put the poor and the homeless at much greater risk than the well-to-do. And air conditioning can also at least partially explain the gradually decreasing trend in heat-related mortality in the US over the past 50 years, the relatively lesser impact of heat stress in southern cities, and the success of early heat wave warning systems.

Of course, running more and more air conditioners causes more of the pollution that causes global warming. Unless and until we have l low-carbon energy sources, we can’t just count on more air conditioning to get us through. And those who can’t cool off with air conditioning will remain at risk. Recent news stories have highlighted multiple heat-related deaths among the homeless in places like Phoenix, which have been experiencing daily temperatures above 110 degrees Fahrenheit. And numerous deaths are being recorded in the Southwest among people trying to enter the country illegally through the sweltering deserts.

Is there a limit to the temperatures the body can tolerate? Probably, but we don’t know what that point is. What is unfortunately likely, though, is that we are going to find out in the coming decades: Some studies suggest climate variability will increase with global warming, so that extremes of heat will become even more frequent, and more extreme.

So we have another public health reason to mitigate climate change; if we can’t get out of the kitchen, at least let’s turn down the oven.