Diverging trends in US summer dewpoint since 1948

Abstract

AbstractIncreases in summer humidity are a basic threat to human survival, because the body cannot shed heat by sweating if absolute humidity is too high. However, climate change trends and patterns of extreme humidity have been much less studied than those of extreme temperature. Here, using station data, we provide an up‐to‐date and comprehensive assessment of the patterns and 1948–2020 trends of summertime dewpoint () in the contiguous United States, for multiple percentiles of its distribution ranging from median to extreme. We find that summer‐median is maximized in the Southeast and along the coasts, while extreme summer is counterintuitively higher in the Midwest than in much of the Southeast, and is higher in Western agricultural valleys than on the Pacific coast. In contrast, 1948–2020 trends in summer are broadly consistent across percentiles, but quite divergent regionally. Namely, median and extreme have strongly increased in Florida, South Texas, parts of California and from the Northeast to the Northern Plains, but have declined in the Intermountain West and changed little elsewhere, often despite clear summertime warming. These regional non‐increases contradict basic theory, but agree with several recent studies. In addition, median is increasing more systematically than extreme in several parts of the eastern United States. Future work will seek to uncover the reasons for all of these divergences and to better understand the fate of summer humidity worldwide.