The contiguous United States recorded its hottest month in history in July, averaging 76.89 degrees Fahrenheit across the Lower 48 states, the National Oceanic and Atmospheric Administration said.
The previous record was set in July 1936, at the height of the Dust Bowl. July's temperature topped that mark by one-eighth of a degree. NOAA records extend to 1895.
Meteorologist Jeff Masters of Yale Climate Connections called the milestone alarming. "It's not good when you're breaking records from the Dust Bowl," Masters said. The 1930s drought and heat wave displaced millions and triggered what Masters called "a cataclysmic event in U.S. history." "If we're exceeding records from the Dust Bowl, that says that we're in deep trouble," he said.
Hotter-than-normal conditions spread across the Lower 48. The most extreme heat concentrated in the Mountain West, Southwest, Northern Plains and Southeast. Every state in the contiguous United States registered at least 1 degree Fahrenheit above its 20th-century average.
Russ Vose, chief of monitoring at NOAA's National Center for Environmental Information, said the heat during the Dust Bowl years was more geographically concentrated in parts of the Midwest, worsened by the agricultural practices of that era.
Scientists attribute the current temperatures to the burning of coal, oil and gas. Katharine Jacobs, a climate scientist at the University of Arizona, said the "extremely high temperatures across the continental U.S. this summer, along with intense drought and fire conditions, are absolutely consistent with the climate change signal."
A key driver of the record was unusually high nighttime lows. NOAA said minimum temperatures broke the previous record by 0.7 degrees—a classic indicator of human-caused climate change, according to scientists.
Masters said overnight temperatures are critical during heat waves. "If you're talking heat waves, that nighttime low is incredibly important for determining total heat stress," he said. When temperatures do not cool at night, the human body lacks sufficient time to recover.
Studies link rising nighttime temperatures to higher mortality rates and sleep deprivation. NOAA calculates average temperatures across a full 24-hour cycle, not just daily highs or lows.
