Killer Heat Grows Hotter around the World

By Gayathri Vaidyanathan and ClimateWire | August 6, 2015

Millions of people around the world are experiencing a scorching summer, as records are broken and thermostats climb this week in parts of Europe. Temperatures in Paris and Brussels exceeded 90 degrees Fahrenheit at a time of year when 70-degree weather is the norm, according to Accuweather.com.

In Bandar-e Mahshahr, Iran, temperatures climbed to 115 °F last week. The temperature, together with high humidity, felt like 163 °F to hapless people directly exposed to the weather, according to Accuweather.

That is the second-highest known “heat index” value ever recorded, said Maximiliano Herrera, a climatologist and weather aficionado who maintains one of the world’s most comprehensive datasets of extreme temperatures. The highest heat-index value ever recorded was 174 °F in 2003 in Dhahran, Saudi Arabia, he said. The highest air temperature in an inhabited area was recorded in Gotvand and Dehloran, Iran, and Turbat and Sibi, Pakistan, in the 1990s, when the thermostat climbed to 127.4 °F (53 degrees Celsius), Herrera said.

In June, Pakistan experienced a heat wave so severe that more than 1,229 people died. A month earlier, temperatures in parts of India climbed up to 113 °F, killing at least 2,500 people.

Including June, four months out of the first six in 2015 have broken global temperature records. July appears to be tracking the trend, even as a strong El Niño has formed, which will exacerbate global temperatures.

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While scientists are still deciphering if particular heat waves, such as the ones in Pakistan and India, could be tied to climate change, it is accepted science that heat waves, broadly speaking, will become more frequent, intense and prolonged with global warming.

They are already the deadliest weather phenomenon in the world. Nine out of 10 heat waves with the most fatalities have occurred since 2000, according to data in EM-DAT, an international disaster database. They have caused 128,885 deaths around the world, according to the database.

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So what is the highest temperature a person can tolerate?

It depends on the amount of heat stress a person undergoes. This, in turn, is dictated not simply by the air temperature, but also by the humidity, wind speed, and the amount of long- and shortwave radiation a person is exposed to.

In a 2010 study in the Proceedings of the National Academy of Sciences, scientists explored the level of temperature and humidity—called the “wet-bulb temperature”—beyond which a human body can no longer dissipate heat by sweating, and the body temperature rises to life-threatening levels.

The scientists found that if humans were to be exposed to wet bulb-temperatures higher than 95 °F (35 ºC) for more than six hours, they would not survive.