Dangerous heat wave grips central and southern United States again

At least 40 million people were under extreme heat warnings across the central and southern United States on Sunday as the same sweltering pattern held for a second straight day. More than 100 million people nationwide were under some form of heat alert, and at least seven large cities were forecast to reach triple-digit highs.

A second day of extreme temperatures gave the body less time to recover, especially when severe humidity makes the air feel hotter than the thermometer shows. That prolonged stress raises the risk of dehydration, heat exhaustion and heatstroke.

On July 24, Climate Central's Climate Shift Index tied human-caused climate change to dangerous heat across much of the United States as hot air spread from the western U.S. eastward into the Midwest and South. Climate Central's Climate Shift Index levels of 5, the highest possible, were forecast across large areas of the country through that period.

Older adults, outdoor workers, children, people without reliable cooling and people with chronic medical conditions faced the greatest risk. For people working outside, the exposure came on top of long shifts in direct sun and humid air. For households without dependable air conditioning, the same stretch of heat that pushed electricity use higher also threatened outages.

Air conditioners run around the clock, pushing power demand higher, while cities open cooling centers and shift operations to protect residents who cannot stay indoors. Construction work, road crews and other outdoor jobs slow down or stop, and daily routines around travel, sports and errands get harder to manage safely.