Millions of TV viewers watched minute-by-minute coverage of Hurricane Ian blasting its path of destruction in Florida, Georgia and South Carolina. But while hurricanes are scary and deadly, extreme heat is a stealthy killer that causes more deaths than all other weather disasters combined. This summer, a record-breaking heat wave baked the western United States, with temperatures soaring past 110°F in some places.
Escalating climate change has made heat waves more frequent and more severe worldwide. Bloomberg reports one-eighth of humanity lived in extreme heat for six months in 2022. Parts of Bangladesh, India, Nepal, and Pakistan suffered temperatures above 104°F. China reported 267 weather stations reached new highs in August, and the country is experiencing another unprecedented heatwave this October.
World Weather Attribution researchers report that climate change made India and Pakistan’s heat wave 30 times more likely to occur. And newly reported research suggests that people may be much more susceptible to heat than previously realized. Another recent study shows human impacts could cause billions of dollars in economic damage.
But the news is not all bad. Other research is helping identify effective strategies to mitigate the impacts of extreme heat and lessen human suffering. Cities are examining ways to cool temperatures, especially in the poorest areas whose residents bear the brunt of heat waves. Some effective solutions are relatively low tech, such as planting more shade trees and hiring city managers to plan effective responses to mitigate suffering during heat waves.
Human tolerance for heat found lower than previously thought
New research has shown that humans may not be quite so tolerant to heat as previously assumed. Many prior climate studies had assumed humans can tolerate a “wet tube” temperature up to 95°F. Obtained by wrapping a piece of wet cloth around the thermometer bulb, the measure accounts for both air temperature and humidity. The wet bulb measure is important because humidity makes it harder for the body to sweat, hindering its natural cooling process, and the actual upper limit may be much less, according to a study by a team of Penn State University researchers.
They exposed 24 healthy, participating adults with a variety of body types to a range of different temperature and humidity levels. They found the heat exposure level that exceeded the body’s natural cooling ability occurred well below 95°F for all subjects. In humid conditions – with air temperature in the range of 96.8°F to 104°F – the critical wet-bulb limit averaged only about 86°F.
In dry conditions with air temperature upward of 122°F, the critical wet-bulb value reached below 79°F. In these hot-dry exposures, the researchers found that the subject’s skin temperatures actually increased more quickly toward critical levels.
These results suggest that people are much less tolerant to extreme heat than previously thought, and that extreme heat limits will vary based on climate conditions and individual physiology.
That’s especially troubling, because while the previous 95°F “wet bulb” benchmark has rarely been exceeded in even the hottest parts of the world, more places are experiencing the lower critical values found to be of concern in this study, meaning more people may be at risk as climate change raises temperatures.
Trouble in particular for outdoor workers
More than 30 million U.S. residents spend most of their time working outside in essential jobs like construction, maintenance, policing, and agriculture. And building wind turbines, installing solar panels and performing other essential work needed to achieve a clean energy transition will require outdoor workers to contend with extreme heat that jeopardizes their health and productivity.
A recent study in the journal Elementa: Science of the Anthropocene analyzed future impacts of extreme heat on this workforce. The authors looked at potential climate trends across the U.S. and the number of working hours that could exceed the temperature thresholds at which the Centers for Disease Control and Prevention recommends reduced workload (heat index above 100°F) or work stoppage (above 105°F). Assuming no change in population, the researchers found workers’ exposure to days with a heat index above 100°F would increase three to four times by mid-century, and four to seven times by late century, depending on emissions.
They calculated that lost working hours could put $39 to $55 billion in worker earnings at risk by 2050. However, economics is just the tip of the iceberg for climate impacts on the outdoor workforce. Outdoor workers receive lower-than-average wages and Black and Hispanic workers experience disproportionately higher heat-related fatalities. As many actions needed to address climate change rely on outdoor work, adaptive work schedules are a climate imperative.
Hope for solutions: Made in the shade?
While changing the weather seems impossible, some cooling solutions are at hand. An effective strategy involves countering the “urban heat island effect” in historically redlined neighborhoods: urban areas with lots of pavement and little vegetation that are harder hit by heatwaves than greener communities.
A 2020 study of 108 U.S. urban areas revealed that historically redlined neighborhoods, with their high concentrations of low-income residents and residents of color, are nearly 5°F warmer than non-redlined areas of the same city. Planting shade trees in these areas can be a powerful tool.
In Atlanta, for instance, researchers from the University of Miami and Georgia State University found summer surface temperatures can vary nearly 14°F between vegetated and non-vegetated areas. Their analysis of planning documents also showcased how efforts to preserve urban tree canopy in predominantly Black or low-income neighborhoods decreased the heat inequities observed in other U.S. cities.
Better city planning to incorporate new vegetation or restore lost tree cover will play an important role in fostering cooler urban environments while righting long-standing inequities.
Expanded need for chief heat officers
Taking heat seriously, and implementing strategies to beat it, will require institutionalizing the practice of heat planning in local government nationwide. For instance, some cities around the world are creating chief heat officer positions to streamline the efforts of different city departments to treat heat like the significant safety risk it is.
From work schedules to city planning, they are exploring and putting into place ways to adapt social life that will protect health and the economy while reducing historical inequities. These strategies are expected to become more important and more common as climate change causes temperatures to rise. At the same time, researchers must continue identifying the limits of human adaptability and potential solutions.
James Arnott is Executive Director of the Aspen Global Change Institute, and Greg Alvarez is Deputy Communications Director with Energy Innovation. Both organizations are Yale Climate Connections content sharing partners.