The first major heatwave of 2025 has arrived, coinciding with the official start of summer, placing over 40 million people across the US under heat alerts. Temperatures are set to soar into the 90s Fahrenheit across the Midwest this weekend, with triple-digit highs anticipated in major East Coast cities like New York, Philadelphia, and Washington, D.C., alongside Denver, as the peak hits early next week. British health officials have also issued heat warnings for the UK, underscoring a global concern.
This escalating heat is not merely an inconvenience; it poses significant health risks, particularly for children, the elderly, and individuals with pre-existing conditions. Climate change, largely driven by the burning of fossil fuels, is exacerbating these extreme weather events, making already hot regions increasingly dangerous. The true measure of heat danger extends beyond simple temperature readings, incorporating factors like humidity, cloud cover, and wind, as captured by the wet bulb globe temperature (WBGT). Even seemingly lower temperatures can be perilous in humid conditions. A critical concern is the lack of overnight reprieve during heatwaves. "Your body needs a reprieve," explained Ashley Ward, director of the Heat Policy Innovation Hub at Duke University. "You don't get that overnight, we start the next day at a deficit." She warned that overnight temperatures failing to drop below 75F (24C) can lead to "pretty extraordinary outcomes with respect to heat illness and heat stroke, and even mortality."
