Which Kills More People: Extreme Heat or Extreme Cold? by Dr. Jeff Masters

Extreme heat and extreme cold both kill hundreds of people each year in the U.S., but determining a death toll for each is a process subject to large errors. In fact, two major U.S. government agencies that track heat and cold deaths--NOAA and the CDC--differ sharply in their answer to the question of which is the bigger killer. One reasonable take on the literature is that extreme heat and extreme cold are both likely responsible for at least 1300 deaths per year in the U.S. In cities containing 1/3 of the U.S. population, a warming climate is expected to increase the number of extreme temperature deaths by 3900 – 9300 per year by 2090, at a cost of $60 - $140 billion per year. However, acclimatization or other adaptation efforts, such as increased use of air conditioning, may cut these numbers by more than one-half.

NOAA’s take: heat is the bigger killer

NOAA’s official source of weather-related deaths, a monthly publication called Storm Data, is heavily skewed toward heat-related deaths. Over the 30-year period 1988 – 2017, NOAA classified an average of 134 deaths per year as being heat-related, and just 30 per year as cold-related—a more than a factor of four difference. According to a 2005 paper in the Bulletin of the American Meteorological Society, Heat Mortality Versus Cold Mortality: A Study of Conflicting Databases in the United States, Storm Data is often based on media reports, and tends to be biased towards media/public awareness of an event.

CDC’s take: cold is the bigger killer

In contrast, the CDC’s National Center for Health Statistics Compressed Mortality Database, which is based on death certificates, indicates the reverse—about twice as many people die of “excessive cold” conditions in a given year than of “excessive heat.” According to a 2014 study by the CDC, approximately 1,300 deaths per year from 2006 to 2010 were coded as resulting from extreme cold exposure, and 670 deaths per year from extreme heat. However, both of these numbers are likely to be underestimated. According to the 2016 study, The Impacts of Climate Change on Human Health in the United States, “It is generally accepted that direct attribution underestimates the number of people who die from temperature extremes.” For example, during the 1995 Chicago heat wave, only 465 death certificates had heat as a contributing cause, while excess mortality figures showed that close to 700 people died as a result of the heat (Figure 2).

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