Heat waves have always been part of summer, but the familiar short periods of oppressive conditions have grown into weeks to months of sweltering heat. Research has shown that heat waves have become longer, hotter and more frequent over the last half a century because of human-induced climate change.
The 2021 Pacific Northwest heat dome, the Central Plains’ summer from hell the following year and this year’s Southwest sizzler are the most familiar recent examples in this country. But extreme heat has touched every continent over the last few years: Temperatures have regularly exceeded 122°F (50° Celsius) across the Asian subcontinent, and London’s thermometers reached 104°F (40°C) for the first time last year, much earlier than climate models predicted.
But will such extended periods of heat and humidity come to regularly test the limits of human tolerance in places where much of the world’s population lives? It could happen sooner than we think.
We can study this question using the wet-bulb temperature, which combines the influence of heat and humidity on the human body.
At 2°C warming, the city of Hudaydah, Yemen, with a population of about 700,000, will experience an average of 340 hours a year of physiologically intolerable heat and humidity, putting the entire population at increased risk of dying. Divided into six-hour increments, that’s equivalent to 56 days a year of these extreme conditions.
Other populous global hot spots at 2°C of warming would include Aden, Yemen, with about 34 days a year of such conditions; Dammam and Jeddah, Saudi Arabia, with 37 and eight days, respectively; Bandar Abbas and Ahvaz, Iran, with 29 and three; Lahore, Pakistan, with 24; Dubai, with 20; and Delhi and Kolkata, India, with 6 and 5.
Even in our current climate, extreme heat is already associated with dire health consequences. A Midwestern heat wave killed 700 people in Chicago in 1995. More than 70,000 died in Europe in the summer of 2003, and in 2010, 55,000 perished due to heat in Russia. More recently, an estimated 1,400 died across Oregon, Washington and British Columbia during the 2021 heat dome, and about 60,000 lost their lives due to extreme heat across Western Europe last year.