Scorching heat and high humidity have madesummers unusually uncomfortable in the Eastern United States, breaking previous records for mugginess.
In recent decades, climate change has significantly increased summer humidity in the Eastern United States, leading to record-breaking daily dew points and overall higher humidity levels.
Since the 1950s, the number of days with dew points at or above 65°F—considered uncomfortable—has surged sharply. Major cities like Philadelphia, Washington, and Baltimore have experienced many more days where dew points reach or exceed 75°F, classified as "oppressive" humidity.
This rise in humidity is due to warmer air being able to hold about 4% more moisture per degree of temperature increase, intensifying heatwaves and leading to warmer, more humid nights that reduce relief from daytime heat. The early summer months of 2025 set new records, with dew points averaging at least 6°F higher than the 1951-2020 norm in several major Eastern cities.
The average June and July humidity for the entire country east of the Rockies rose to more than 66 degrees, a record since measurements started in 1950. What was mostly missing was the occasional cool front that pushes out the most oppressive heat and humidity.
Higher humidity also has broader impacts. It can lead to increased economic strain due to energy grid stress and disruptions in agriculture and construction, as well as elevated health risks related to heat stress. Additionally, regional factors such as increased agricultural irrigation and land use changes contribute locally to humidity rises through evapotranspiration, making hot days feel muggier and preventing cooler nights.
The South gets more 65-degree dew points in the summer than the North, but that's changing, and uncomfortable humidity is moving further north. Summers now are not the summers that your grandparents experienced, according to University of Georgia meteorology professor Marshall Shepherd.
Parts of 27 states and Washington, D.C., had a record amount of uncomfortable days in June and July. The Midwest and East were stuck under either incredibly hot high pressure systems or getting heavy and persistent rain in amounts much higher than average for most of the summer.
Nighttime temperature has a significant impact on the body, and a lack of cooling can prevent recovery from a hot afternoon. High humidity didn't allow the air to cool at night as much as usual, contributing to multiple nighttime temperature records.
In four of the last six years, the average dew point has been near and even over the uncomfortable line of 65 degrees. The seemingly small increase in average dew points means the worst ultra-sticky days that used to happen once a year, now happen several times a summer.
References:
[1] Shepherd, M. (2021). Climate Change and Extreme Weather. In Encyclopedia of Weather and Climate (pp. 1-10). Elsevier.
[2] National Centers for Environmental Information. (2021). U.S. Climate Extremes Index. Retrieved from https://www.ncdc.noaa.gov/cdo-web/datatools/climextreme
[3] National Oceanic and Atmospheric Administration. (2021). U.S. Summer Temperature and Precipitation. Retrieved from https://www.ncdc.noaa.gov/cdo-web/datatools/us_summer_climate
[4] Environmental Protection Agency. (2021). Climate Change Indicators: Humidity. Retrieved from https://www.epa.gov/climate-indicators/climate-change-indicators-humidity
[5] Intergovernmental Panel on Climate Change. (2014). Climate Change 2014: Impacts, Vulnerability and Adaptation. Retrieved from https://www.ipcc.ch/report/ar5/wg2/
- The steep rise in uncomfortable humidity days, particularly in the Eastern United States, could indicate a shift in the climate, potentially reflecting the broader impacts of environmental science and climate-change.
- The increasing trend of high dew points and oppressive humidity levels in summer, as well as the associated heatwaves and extreme weather events, might be linked to the warming of the environment, a critical aspect of science and climate-change research.
