{"id":441072,"date":"2026-04-23T09:35:55","date_gmt":"2026-04-23T16:35:55","guid":{"rendered":"https:\/\/climatescience.press\/?p=441072"},"modified":"2026-04-23T09:35:57","modified_gmt":"2026-04-23T16:35:57","slug":"u-s-temperature-extremes-have-declined-since-1899-new-study-challenges-assumptions-about-increasing-heatwaves","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=441072","title":{"rendered":"U.S. Temperature Extremes Have Declined Since 1899: New Study Challenges Assumptions About Increasing Heatwaves”"},"content":{"rendered":"
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A new peer-reviewed paper by John R. Christy (University of Alabama in Huntsville, retired Alabama State Climatologist) examines daily temperature extremes across the contiguous United States (CONUS) from 1899 to 2025. <\/p>\n\n\n\n

Published in Theoretical and Applied Climatology, it analyzes over 40 million raw daily observations from an expanded and gap-filled U.S. Historical Climatology Network (USHCN) dataset of 1,211 stations (97.6% coverage, each with at least 92% data completeness). No homogenization, spatial interpolation, or temporal adjustments were applied to the station-level data\u2014only inverse-distance weighting on a 0.5\u00b0 grid to aggregate while preserving local signals.<\/p>\n\n\n\n

This is a peer-reviewed paper<\/em><\/strong> by John R. Christy<\/em><\/strong> (University of Alabama in Huntsville, retired Alabama State Climatologist), published in Theoretical and Applied Climatology<\/em><\/strong> (2026, open access).<\/p>\n\n\n\n

Declines in hot and cold daily temperature extremes in the conterminous US, 1899\u20132025 <\/strong><\/a><\/p>\n\n\n\n

Springer Nature Link<\/a><\/p>\n\n\n\n

Published:<\/strong> 18 April 2026<\/p>\n\n\n\n

Volume 157, article number 309, (2026)<\/p>\n\n\n\n

DOI:<\/strong> 10.1007\/s00704-026-06200-3<\/p>\n\n\n\n

By John R. Christy<\/a><\/p>\n\n\n\n

Abstract<\/strong><\/p>\n\n\n\n

Knowledge of temperature extremes, and their potential changes within a climate system of increasing greenhouse gases, is of vital interest for humans and the infrastructure which supports them. To produce a better understanding of how daily extreme temperatures have changed over time in the conterminous US (CONUS), the United States Historical Climate Network (USHCN) database was extended back to 1899 and forward to 2025. The original 1,218 stations, selected in the 1980s by NOAA as capable of addressing climate concerns, have since been neglected – almost half of the stations have closed since 2000. Incomplete station records were supplemented with nearby stations with high correlation and removeable biases to provide time series for 1,211 of the stations with at least 92% of data present. Extreme temperature metrics for summer daily maximum temperatures and winter daily minimum temperatures were calculated. The general result is that metrics for extreme summer heat, e.g., hottest values, number of heatwave days, etc., show modest negative trends since 1899. Extreme cold temperature metrics also indicate a decline in their occurrences especially since the 1990s. In sum, instances of both hot and cold extreme metrics have declined since 1899. To demonstrate an application of this dataset we examined the claims of one source regarding changing temperature extremes, The National Climate Assessment 5<\/em>.<\/p>\n\n\n\n

Data and Methods<\/strong><\/p>\n\n\n\n

Christy extended the U.S. Historical Climatology Network (USHCN) dataset\u2014originally ~1,218 stations selected by NOAA in the 1980s for climate monitoring\u2014to cover December 1898\u2013March 1899 through summer 2025. Nearly half the stations have closed since 2000, so he supplemented incomplete records by “threading” data from highly correlated nearby stations (median correlations ~0.93 for daily Tmax, ~0.89 for Tmin), with small biases adjusted. This yielded 1,211 stations with at least 92% data completeness (median 98%).<\/p>\n\n\n\n