For tens of millions of Americans this week, summer is starting with a multiday blast of fierce heat. Temperatures in parts of the country are likely to be well into the 90s through the weekend. The National Weather Service has warned that the heat wave could be the longest one some places have experienced in decades.
Weather this hot creates plenty of health risks, even for people who sweat through it for just a few hours. But researchers have found that the dangers of heat can be compounded when conditions are sweltering for day after grinding day, night after sleepless night. With so much of the United States facing such hazards this week, it’s a good time to linger a bit on what we know about heat that lingers.
In general, human-caused global warming is making heat waves even hotter, more frequent and longer lasting. Already this year, India has experienced what its top weather official described as the country’s longest hot spell on record, spanning 24 days in April and May. Greece is in its second week of deadly heat, less than a year after experiencing a 16-day heat wave, the longest it has measured.
For the planet as a whole, 2023 was the warmest year in human history and global temperatures have continued breaking monthly records well into 2024.
When it’s very hot, the human body has to work harder to keep organs and tissues at their normal healthy temperatures. The longer your body is forced to do this, the greater the strain on your cardiovascular system, and the higher the risk of negative health effects, which, in extreme cases, can include heart and kidney failure.
How much more risk? Two researchers, G. Brooke Anderson and Michelle L. Bell, crunched the numbers for 43 U.S. communities between 1987 and 2005. They found that for every additional day that a heat wave dragged on, the risk of nonaccidental death rose by 0.4 percent. For every extra degree Fahrenheit above normal temperatures, the risk increased by 2.5 percent. Both effects were more pronounced in the Northeast than in the Midwest or South, the researchers found, possibly because people there were less accustomed to stifling weather.