The first significant heat wave of 2025 has arrived, coinciding with the official start of summer. Over 40 million people in the United States were under heat alerts as temperatures in the Midwest were expected to soar into the 90s Fahrenheit (30s Celsius) during the weekend. Triple-digit highs were also anticipated in cities like New York, Philadelphia, Washington, and Denver, with the peak expected on the East Coast early next week. British health officials have issued similar heat warnings for the U.K.
Climate change is intensifying heat waves, with an increasingly hot planet primarily due to the combustion of fossil fuels such as coal, oil, and natural gas. This results in already hot regions becoming even more unbearable. The implications of heat extend beyond just the cancellation of events; it poses a serious health risk, particularly for vulnerable populations such as children, elderly individuals, and those with pre-existing health conditions.
Understanding when heat becomes dangerous involves more than just temperature reading. A comprehensive measurement known as wet bulb globe temperature (WBGT) accounts for variables such as temperature, humidity, cloud cover, and wind. While heat index, which measures temperature and humidity together, is less detailed yet easier to access through weather applications, both serve to illustrate why conditions can be more hazardous in humid territories compared to drier areas on seemingly equal temperature days. For instance, a shaded soccer field in 90-degree F (32-degree C) Phoenix could be safer than an exposed park in 80-degree F (27-degree C) Little Rock.
According to NOAA, prolonged exposure to a heat index of 96 degrees F (36 degrees C) coupled with 45% humidity falls within the “danger” category for strenuous activity. Recent research indicates that even young, healthy individuals may struggle to endure extended hours under high heat and humidity.
Overnight lows can pose particular danger during a heat wave. Ashley Ward, director of the Heat Policy Innovation Hub at Duke University, emphasizes that our bodies require a break from the heat to recover, and when nighttime temperatures remain high, it can lead to severe heat illness, heat stroke, and even mortality. Ward recommends finding air conditioning for relief, but notes that access can often be overestimated by census data.
If whole-house cooling is unaffordable, Ward suggests establishing a "cool corner" to provide a restful area for sleep, preparing for the upcoming heat of the day. While evaporative or "swamp" coolers can assist in dry heat, they may increase humidity. For regions with high humidity, using a fan is more effective. Public spaces with air conditioning, such as movie theaters, malls, and libraries, can also provide relief during heat waves, and some communities offer cooling centers.
Economic assistance may be available for low-income households to purchase air conditioning units through programs like the Low-Income Home Energy Assistance Program (LIHEAP). Local nonprofits and civic organizations may also provide access to cooling equipment.
For those working outside, it’s crucial to be aware of workplace protections. Currently, there are no federal regulations regarding heat safety for workers in the U.S., although some states, including Washington, Oregon, California, Nevada, Colorado, Minnesota, and Maryland have set their own heat safety standards. Understanding these regulations can be difficult, and enforcement remains a significant challenge for many workers.
Staying hydrated and managing body temperature are essential for outdoor workers. This could involve drinking plenty of fluids, wetting clothing, or applying cold water on pulse points such as the neck, hands, and feet. If engaging in physical activity, it is advisable to avoid the hottest parts of the day and to carry ample water.
Recognizing the symptoms of heat illness is vital. Early warning signs can include heavy sweating, muscle cramps, and headaches, which should prompt individuals to cool off immediately. More severe symptoms can escalate to heat exhaustion, characterized by rapid heart rate and dizziness, and can lead to life-threatening heat stroke, which may present confusion and fainting. In such cases, calling emergency services is critical.
The heat wave affects millions and serves as a stark reminder of the ongoing challenges posed by climate change. Awareness and proactive measures can support public health and safety during these extreme weather events.
