A new peer-reviewed study by Dr. John R. Christy (University of Alabama in Huntsville, retired Alabama State Climatologist) finds that both extreme heat and extreme cold temperature metrics across the contiguous United States (CONUS) have shown overall declines since 1899.

Christy analyzed over 40 million daily temperature observations from the U.S. Historical Climatology Network (USHCN), using 1,211 stations with high data completeness (at least 92% of days). The record spans December 1898 through recent years (up to ~2025 in the analysis).

Published in Theoretical and Applied Climatology:

Extreme summer heat metrics (hottest annual temperatures, number of daily heat records, heatwave days, duration/intensity of heat events based on daily TMax): Modest negative (declining) trends since 1899. No long-term increase in extreme summer heat. The most intense nationwide heat events were concentrated in the 1925–1954 period, especially the 1930s Dust Bowl era (e.g., 1936 stands out prominently).

Extreme winter cold: Metrics for cold extremes (based on TMin) show a decline in occurrences, especially sharp since the 1990s, with fewer record lows and less severe cold events.

Overall: Instances of both hot and cold temperature extremes have declined over the 127-year period. The climate over the CONUS has become less impacted by temperature extremes. The range between the hottest and coldest annual temperatures has narrowed by about 6°F (~3.3°C). The sum of extreme heat and cold days has dropped substantially (roughly on the order of a 30% reduction from mid-20th-century peaks).

Regional notes: Some recent increases in heatwave activity in the western US, but long-term declines in central and eastern regions. The study contrasts with some claims in the National Climate Assessment 5.

Christy attributes heat trends largely to strong natural variability (early 20th-century peaks), while cold declines may involve a mix of urbanization/land-use effects around stations (affecting nighttime lows more) and possible GHG influences warming the coldest air preferentially. He cautions that natural variability remains large relative to any small GHG-driven warming signal for these regional extremes.

This paper adds a valuable, station-dense, long-term observational dataset focused on actual extremes rather than averages or model projections. It challenges narratives of steadily worsening heat disasters across the US while confirming fewer brutal cold snaps—a net reduction in temperature-related stress in some respects. For the full details, see the paper in Theoretical and Applied Climatology (Christy 2026). Data like this underscores the importance of examining full historical records rather than short recent periods or media-highlighted events.

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Declines in hot and cold daily temperature extremes in the conterminous US, 1899–2025

“Declines in hot and cold daily temperature extremes in the conterminous US, 1899–2025” is the title of a 2026 peer-reviewed paper by Dr. John R. Christy (University of Alabama in Huntsville, retired Alabama State Climatologist) published in Theoretical and Applied Climatology.

Published: Theoretical and Applied Climatology  18 April 2026

Author: Dr. John R. Christy

DOI:10.1007/s00704-026-06200-3

Volume 157, article number 309, (2026)

Christy constructed a dataset from the U.S. Historical Climatology Network (USHCN), extending it back to the winter of December 1898–March 1899 and forward through the summer of 2025. The analysis covers the conterminous United States (CONUS) using 1,211 stations with high completeness (at least 92% of days filled via supplementation from highly correlated nearby stations where needed).

This yielded over 40 million daily temperature observations.

• Heat extremes focused on daily maximum temperatures (TMax) during summer.
• Cold extremes focused on daily minimum temperatures (TMin) during winter.
• Metrics examined include: hottest annual values, number of daily record highs/lows, heatwave/cold wave days (duration and intensity), spatial coverage of extremes, and overall frequency of extreme events.

The study also compares results against claims in the National Climate Assessment 5.

Abstract

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.