Worsening heat waves are projected to be a growing health threat to humans as the world warms from climate change, according to two recent studies.
These studies projected that as the average global temperature increases, heat waves will become more frequent, hotter, of longer duration, and more widespread. This means both that more people will face heat waves, and that more people will likely die from heat-related causes during them.
In one study, published in Nature Climate Change in May 2017, researchers in the U.S. and Great Britain analyzed heat wave data from 164 cities worldwide from 1980 to 2014 to pinpoint the threshold at which heat and humidity become potentially deadly. The cities were mostly located in the temperate (not tropical) mid-latitudes of the Northern and Southern hemispheres, and included such population centers as New York, Chicago, Beijing, Sao Paulo, and Moscow. The researchers determined that 30 percent of the world’s population is currently exposed to heat waves that exceed this threshold for at least 20 days per year. That number will grow to 48 percent by the year 2100, the researchers projected—and that’s counting on a drastic reduction worldwide of greenhouse gas emissions, the major controllable factor behind climate change. If nothing is done to reduce greenhouse gases, the researchers estimate that 74 percent of the world’s population will face such heat waves.
The second study, in a June 2017 edition of Science Advances, used India’s climate data from 1960 to 2009 to predict the relationship between the number of heat wave days each year and heat-related mass mortalities, defined as the deaths of more than 100 people during a singleheat wave. Unsurprisingly, as temperature and duration of heat wave events increased, so did the probability of large numbers of people dying. An increase in annual heat wave days from six to eight, for example, was correlated with a 78 percent increase in the probability of heat-related mass mortalities.
The most important action recommended by both sets of researchers is, not surprisingly, to reduce greenhouse gas emissions to limit the increase in global temperature. Aside from efforts to meet greenhouse gas goals, governments will need to invest in ways to keep their populations safe during heat waves. India faces a particular challenge, since approximately one-quarter of its population does not have access to electricity and therefore air conditioning or electric fans.
Also see Climate Change and Mental Health.