The biggest threat of the summer isn’t sharks or ticks or hideous tan lines — it’s heat. According to the National Oceanic and Atmospheric Administration, hot weather is the number one summertime killer in the United States. Hundreds of people die each year from heat-related causes, most of them elderly or mentally ill.
New research from the University of Hawaii shows that the number of these deadly heat waves is only going to increase. The study, published today in Nature Climate Change, found that unless current rates of greenhouse gas emissions are lowered, the majority of the world’s population will experience temperatures extreme enough to be fatal by the end of this century.
“Thirty percent of the world’s human population is exposed to these deadly conditions at least 20 days in a year,” said lead researcher Camilo Mora, associate professor of Geography in the College of Social Sciences at the University of Hawaii at Manoa, in a statement. “If we don’t do anything, it’s going to be close to seventy percent.”
Hyperthermia, the scientific term for high body temperature, can occur both indoors and outdoors. Heat stroke, the most extreme and deadly form of hyperthermia, occurs when body temperature rises above 103 degrees Fahrenheit. And it’s not just heat that is dangerous. High levels of humidity can be fatal as well, because it interferes with the evaporation of sweat. The higher the humidity, the lower the temperature needs to be in order to cause heat stroke.
“Imagine it as a sunburn inside your body,” Mora told Seeker. “A lot of the organs will start not working properly.”
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Several headline-grabbing heat waves have occurred over the past few decades, including a devastating European heatwave in 2003 that killed up to 70,000 people. Other places that have experienced these large-scale deadly events include Moscow and Chicago.
Mora and his team at the University of Hawaii at Manoa were just trying to do a simple analysis of locations that had experienced heat waves when they realized that the number of deadly heat events around the world was far more than anyone had realized. They found almost 2,000 locations across the world where people have died from heat-related illness since 1980, including New York, Beijing, and San Paolo in northern Italy.
The researchers used their findings to develop a threshold at which temperatures and humidity become deadly. If greenhouse gas emissions are not reduced, 74 percent of humans will experience temperatures beyond that threshold by 2100. Mora and his team also developed an interactive map that visualizes the projected number of deadly heat days around the globe.