Cohen et al. (2025) Reply to: Observed warming of cold extremes is not captured with a fixed threshold definition

Identification

• Journal: Communications Earth & Environment
• Year: 2025
• Date: 2025-10-08
• Authors: Judah Cohen, Laurie Agel, Mathew Barlow, Dara Entekhabi
• DOI: 10.1038/s43247-025-02630-5

Research Groups

• Atmospheric and Environmental Research, Inc., Lexington, MA, USA
• Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
• Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA, USA

Short Summary

This paper replies to a critique regarding the definition of cold extremes, re-examining trends in Arctic and mid-latitude cold extremes using a moving threshold definition, and concludes that the original findings of inconsistent warming in mid-latitude cold extremes remain robust.

Objective

• To respond to a critique concerning the methodology for computing trends in cold extremes and to re-evaluate these trends using a moving threshold definition for cold extremes.

Study Configuration

• Spatial Scale: Arctic region (70–90°N) and Central and Eastern United States (CEUS) region (30–50°N, 250–285°E).
• Temporal Scale: 1960–2023.

Methodology and Data

• Models used: Not applicable (different statistical methodologies for defining cold extremes were applied: fixed threshold vs. moving (decadal) threshold).
• Data sources: ERA5 reanalysis data (approximately 30 km resolution).

Main Results

• When using a moving (decadal) threshold for defining cold extremes:
  • In the Arctic, both cold extremes and mean temperatures have steadily warmed, with post-2010 cold extremes not reaching the severity of those observed before 1980.
  • In the CEUS, cold extremes and mean temperatures show a step-function warming, remaining steady from 1960 through 1990 and again steady from 1990 through the present at a warmer temperature.
  • Visually, no trend in cold extremes was observed in the CEUS post-1990, even with a moving threshold, and recent cold extremes are comparable to those from previous decades back to 1960.
• Comparison between fixed and moving threshold methods for the CEUS and SSNC regions showed little difference in trends during the period of Arctic Amplification (AA).
• In seven of eight computed trends for the CEUS and SSNC regions using both definitions for the recent period, no statistically significant warming trend was found.
• The alternative derivations of cold extremes do not produce contradictory results or conclusions regarding the inconsistent warming of cold extremes in several mid-latitude locations.

Contributions

• Provides a detailed response to a methodological critique, enhancing the robustness of previous findings on cold extreme trends.
• Emphasizes the importance of using multiple metrics and approaches for a comprehensive understanding of changes in extreme events.
• Reinforces the conclusion that while global warming leads to detectable warming of cold extremes, this warming is not consistently linked to Arctic Amplification in several mid-latitude regions, even when using alternative definitions of cold extremes.

Funding

• The paper does not explicitly list specific funding projects, programs, or reference codes.

Citation

@article{Cohen2025Reply,
  author = {Cohen, Judah and Agel, Laurie and Barlow, Mathew and Entekhabi, Dara},
  title = {Reply to: Observed warming of cold extremes is not captured with a fixed threshold definition},
  journal = {Communications Earth & Environment},
  year = {2025},
  doi = {10.1038/s43247-025-02630-5},
  url = {https://doi.org/10.1038/s43247-025-02630-5}
}