64% of Americans are now exposed to extreme heat. Here's why that's worrying

U.S. cities are experiencing more heat waves every year. In the 1960s, cities endured an average of two heat waves per year. That number has grown to an average of six each year during the 2010s and 2020s, according to the EPA. Cities are particularly vulnerable to more heat waves because of factors like urban heat islands, an effect that makes urban areas hotter than surrounding rural regions. Many factors contribute to urban heat islands: darker surfaces like asphalt and roof shingles—which absorb rather than reflect heat—less shade from trees, and fewer plants emitting cooling moisture from their leaves.

In addition to heat waves becoming more frequent, heat wave seasons have also become longer. In the 1960s, heat wave seasons lasted an average of 24 days a year. In the 2020s, that number has risen to more than 70 days a year. The expansion of heat wave seasons can be dangerous, since it widens the window for extreme temperatures during unusual times of the year. This can lead to situations in which people are not prepared, leaving them vulnerable.

The increased frequency of heat waves and length of heat wave seasons has inspired some cities to take action. In 2021, the mayor of Miami-Dade County appointed a chief heat officer, the first in the nation. This position is intended to strategize ways of keeping people safe from increasingly intense heat events in a city that is experiencing some of the worst heat waves in the country.

Longer heat waves have grave consequences for people's health and safety, particularly for those who are unhoused or who don't have access to air conditioning. Living for prolonged periods at very high temperatures without being able to cool off can increase the risk of heat-related illness and even death. To make matters worse, record-breaking heat during the nighttime has been reported across the country, removing the usual respite from heat offered by the sun going down, and adding to the danger already caused by several days of extreme temperatures.

The intensity of heat waves has steadily climbed over the past six decades. Both in regions accustomed to some amount of extreme temperatures, like the South, as well as in areas which have not previously experienced high temperatures, heat waves have become hotter and more deadly.

In 2021, the Pacific Northwest, a region known for its moderate weather, saw a blistering heat wave that peaked between 116 and 118 degrees Fahrenheit. The event caught many people unprepared, and hundreds of deaths were reported in Oregon and Washington, particularly among people who did not have access to air conditioning. Other cities in California and other parts of the Western U.S. experienced extreme heat waves in September 2022, making it the hottest September on record for the West.

Heat is the leading extreme weather-related cause of death in the U.S. The EPA estimates that between 600 and 1,300 deaths occur in the U.S. every year from extreme heat. Heat-related illnesses and deaths can happen when the body loses its ability to regulate its internal temperature. Dehydration and increased internal temperature can cause blood thickening, which leads to organ and heart damage.

Extreme heat waves impact much more than people's ability to be outside without air conditioning. They also have serious environmental, agricultural, and energy-related ramifications. Heat waves harm crops, cause issues with plant growth, and make it difficult for livestock to survive. They also exacerbate drought, creating water shortages and conditions that are conducive to wildfires and other natural disasters.

Energy systems can also be strained by an increased need for high-energy utilities like air conditioning, with demand outstripping supply in some cases. In July 2022, Texans were instructed to conserve as much energy as possible to alleviate strain on the power grid as temperatures neared 110 F.

As extreme heat events continue to become more frequent and severe, experts caution that being prepared for intense heat waves is one of the best ways to keep people safe. On an institutional level, the CDC recommends having early heat wave alerts in place on a city or county level to warn residents of impending extreme heat risks. This would also enable public cooling centers to open at appropriate times, a vital measure for those without air conditioning and people experiencing homelessness. Keeping hydrated and avoiding the outdoors during heat waves is especially important.

At the same time, measures can be taken to prevent the continued rise of temperatures, as well as to mediate the risks of straining energy systems. Increasing energy efficiency and forms of renewable energy would prevent power grids from being overwhelmed while limiting further emissions, which contribute to rising temperatures in the first place. Introducing more trees and vegetation to urban areas could also work to introduce shade, increase air quality and reduce the harm of emissions, and limit the impact of urban heat islands.