This summer, hundreds of millions of people around the globe are feeling the effects of climate change. Last week in the U.S., more than half of states were under heat advisories, and across the nation, 60 daily high temperature records were tied or broken.
The footing and chains of the 165-year-old Hammersmith Bridge were covered in insulating foil to prevent further cracking, as the UK passes 40°C for the first time. (July 2022) | Credit: Ian Alexander
In parts of Europe, extreme temperatures caused roads and runways to melt and rail lines to warp. Last week, extreme heat caused train tracks in London to expand and buckle, as temperatures on the rails reached nearly 120°F, according to Network Rail, an organization that manages the railway infrastructure in England, Scotland, and Wales. As temperatures rose to 40 °C (104 °F) in London, engineers were forced to wrap the 165-year-old Hammersmith Bridge in foil to reflect the sun and keep its metal frame from cracking. Much infrastructure was designed for temperatures of the last century and not prepared for global warming.
Many people are also ill prepared for the risk excessive heat will pose to their bodies—especially when combined with humidity. This is especially true for the elderly and communities of color who live in urban heat islands without access to air conditioning or cooling centers.
When it gets hot, we sweat to cool down because evaporating water moves heat away from our skin. But if the air is humid, the process slows down, and the point at which heat combined with humidity becomes dangerous, is measured as the "wet-bulb temperature." Wet-bulb temperature was originally measured by wrapping a wet cloth around the bulb of a thermometer and exposing it to air. As water evaporated from the cloth, the thermometer recorded the drop in temperature. The higher the relative humidity, the less moisture evaporated before the bulb and the surrounding air are the same temperature.
A study published in 2010 estimated that a wet-bulb temperature of 35° Celsius—equivalent to when it’s 95° Fahrenheit with 100 percent humidity or 115 °F at 50 percent humidity—would make it nearly impossible for sweat to evaporate, risking heat stroke or death in as little as six hours.
But a recent study from Penn State recently found that temperatures as low as 87 degrees with 100 percent humidity could be life-threatening—even for healthy young people. The wet-bulb temperature for older populations, who are more vulnerable to heat, is likely even lower.
As the planet warms, heat waves are becoming more frequent and intense, but a 2020 study in Science Advances looking at global temperature data found that over the last 40 years, heat combined with high humidity is also increasing.
Below are the symptoms of heat-related illnesses:
Heat exhaustion can happen after several days of exposure to high temperatures and not enough fluids. Symptoms can include: high body temperature, rapid breathing and heart rate, muscle cramps, headache, dizziness or lightheadedness, pale skin, nausea, and fatigue.
Heat stroke is a life-threatening illness in which body temperature may rise above 106 °F (41 °C) in minutes. Unlike heat exhaustion, a heat stroke requires immediate medical attention. Symptoms include: confusion or agitation, hallucinations and an altered mental state, inability to sweat, dry, red skin, dizziness or fainting, slurred speech, very high body temperature (more than 105 degrees F), and seizures.