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WASHINGTON (AP) – A record-breaking surge in humidity is expanding across the United States, contributing to increasingly oppressive summer conditions, according to climate scientists. This shift is extending the reach of uncomfortable heat indices further north and into regions historically unaccustomed to such levels of moisture, raising concerns about public health and infrastructure.

The summer of 2024 saw prolonged periods of extreme heat and humidity across much of the Midwest and Eastern U.S., with many areas experiencing temperatures well above average. According to the National Weather Service, July 2024 ranked as the hottest month on record globally, with numerous cities, including Philadelphia, Pennsylvania, and Newark, New Jersey, experiencing multiple days exceeding 100°F (37.8°C) with heat index values soaring above 110°F (43.3°C). The lack of frequent cool fronts to break the heat and humidity was a key factor, explained Dr.Steve Taylor, a climate scientist at the National Centers for Environmental Data (NCEI) in Asheville, North Carolina.

Traditionally,the Western U.S. has remained drier, and the Southern U.S.has experienced higher dew points. However, this pattern is evolving. Scientists are observing a northward creep of high humidity levels, impacting states like Michigan, Wisconsin, and even parts of New England. This means more frequent and intense heat waves for populations less prepared for such conditions.

“Summers now are not your grandparents’ summers,” stated Dr. Marshall Shepherd, a professor of meteorology at the University of Georgia in Athens, Georgia. He emphasized that the increasing humidity exacerbates the effects of heat, making it harder for the human body to cool itself through evaporation. This poses a particular risk to vulnerable populations, including the elderly, children, outdoor workers, and individuals with pre-existing health conditions.

The increase in humidity is linked to a warming climate, as warmer air can hold more moisture. Rising sea surface temperatures in the Gulf of Mexico and the Atlantic Ocean are contributing to increased evaporation, providing more moisture for the atmosphere. Data from the National Oceanic and Atmospheric Governance (NOAA) shows a consistent upward trend in atmospheric moisture content over the past several decades.

Beyond human health, the increased humidity also impacts infrastructure. Higher humidity can accelerate corrosion of metal structures, increase the risk of mold growth in buildings, and strain energy grids due to increased demand for air conditioning. The American Society of Civil Engineers (ASCE) has highlighted the need for infrastructure upgrades to address the challenges posed by a changing climate, including increased humidity.

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