Too Hot to Handle

Heat waves are becoming more frequent and deadly (suddenly winter seems a lot less threatening).

February 09, 2015

We need a new phrase to describe prolonged periods of extremely high temperatures. “Heat wave” conjures up images of people fanning themselves on the front porch, surrounded by moist glasses of iced tea and lemonade, or dancing to Martha and the Vandellas. Tell someone it’s going to be bitterly cold, and they imagine clinging to life in a parka and a balaclava, with ice accumulating on their eyelashes.

I’m not sure why cold is so much scarier than heat, but the evidence is everywhere. We say hyperbolically that we’re “freezing to death,” but there’s no equally common phrase involving death from heat. The myth that being cold can cause a viral infection is one of the most persistent in our culture, but your grandmother never said, “Take off that knit cap or you’ll get sick!” Even our government policies reflect our overactive dread of the cold. The government spends nine times as much money trying to keep poor people warm as it does trying to cool them off. An extreme fear of cold seems to be hardwired into our lizard brains.

We should start approaching extreme heat with the same trepidation—things are bad and getting worse. For a new study in the journal Environmental Research Letters, a team of international researchers examined temperature data between 1973 and 2012 for evidence of urban heat waves. They defined “heat wave” not as a time of increased lemonade consumption but as a period of six or more consecutive days with daily highs in the 99th percentile of the sample. Yeah, that’s hot.

The findings are startling. Heat waves increased every decade in the 217 urban areas studied, and the rate of increase seems to be accelerating. The most recent four years in the study were all among the five with the most heat waves. Extreme cold and wind, by contrast, were down.

The news is not entirely surprising, of course. We call it global warming for a reason. Temperatures are rising in many places. All 10 hottest years on record have occurred between 1998 and now—and we haven’t seen a record cold month since 1916. Nevertheless, the rise in extreme heat is a special concern, because this can lead to preventable deaths.

How many deaths? Good question. The truth is, nobody really knows. Extreme heat is usually an indirect cause of death—it makes people who are already weakened by youth, old age, or a variety of illnesses more likely to die. Epidemiologists also quibble over the right way to describe the deaths themselves. Some argue a heat wave that advances the death of a nonagenarian by a few months isn’t the same as a snowstorm-induced car accident that kills a teenager. Others say premature deaths are all tragedies and should be treated the same.

Despite these complications, there's some data on heat-related deaths: NRDC (disclosure) estimates that each year there are 400 directly related to heat in the United States, and 1,800 from illnesses worsened by heat. The Centers for Disease Control and Prevention estimates 666 heat deaths annually between 2006 and 2010. But the numbers vary considerably year to year, since extreme heat waves are unpredictable. A single English heat wave killed as many as 760 people in 2013, according to researchers at the London School of Hygiene and Tropical Medicine.

OK, OK—even with heat waves rising, about twice as many Americans die from cold as from extreme heat. (At least, that’s how the CDC sees things.) But the new study suggests heat is soon going to overtake cold mortality. In 2013, another group of researchers calculated that deaths from heat waves would rise by a factor of 10 in 45 years, blowing away deaths from cold.

The classic lyric “It’s like a heat wave, burning in my heart” is about to take on a much darker meaning.


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

Join Us

When you sign up you'll become a member of NRDC's Activist Network. We will keep you informed with the latest alerts and progress reports.