Extreme Heat Dome Grips South, Southwest as Climate Toll Grows

More than 80 million people across the United States are under an Extreme Heat Warning or Heat Advisory this week, the National Weather Service said, as a heat dome the agency's Weather Prediction Center called "steamy...even by mid-to-late August standards" grips the South-Central states and expands into the Southwest.

Daytime temperatures are expected to climb well above 100 degrees Fahrenheit across the Southern Plains and Lower Mississippi Valley through midweek, with parts of the desert Southwest, including Arizona and New Mexico, on track to break heat records with highs of 110 degrees or more by week's end.

Forecasters say nighttime temperatures are also failing to drop, giving residents little overnight relief and raising the risk of heat-related illness. The heat index — what temperature feels like when humidity is factored in — could reach 105 to 115 degrees in southern Arizona and much of Texas, Louisiana and northern Florida.

Scientists say the link between such heat waves and human-caused climate change is among the clearest in extreme-weather research. Michael Wehner, a senior scientist at Lawrence Berkeley National Laboratory, told NPR that for "garden variety" heat waves in the U.S. — such as the hottest day of the year — climate change has raised temperatures by 3 to 5 degrees Fahrenheit.

The average number of heat waves the U.S. experiences has doubled since the 1980s, according to NPR's climate desk, and the most intense heat waves recorded in recent years, including last June's extreme heat in Europe, would have been virtually impossible without human-caused warming, per the World Weather Attribution group.

Heat-related deaths are widely believed to be undercounted and, combined, kill more Americans than hurricanes, wildfires and floods. Humid heat is especially dangerous because sweat cannot evaporate to cool the body when both temperature and humidity are high.

NPR noted that the Trump administration has made significant cuts to NOAA and the National Weather Service, agencies that provide forecasting and warnings during such events.