Admasu et al. (2026) An assessment of Northern Hemisphere warm spell trends across seasons: spring warm spells increasing faster than projected

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Environmental Research Letters
• Year: 2026
• Date: 2026-10-14
• Authors: Lualawi Mareshet Admasu, Rachel H. White, Anaïs Orsi
• DOI: 10.1088/1748-9326/aeb436

Research Groups

[Information not available from the abstract.]

Short Summary

This study assesses trends in warm spells across all seasons in Northern Hemisphere mid-latitude land using observational data and CMIP6 climate models. It finds that observational data show increasing warm spell days in all seasons, but CMIP6 models significantly underestimate spring trends and overestimate fall trends, with these biases linked to seasonal mean temperature, surface albedo, and soil moisture biases.

Objective

• To assess trends in warm spells in all seasons across Northern Hemisphere mid-latitude land using observational data (Berkeley Earth and ERA5) and CMIP6 climate models.

Study Configuration

• Spatial Scale: Northern Hemisphere mid-latitude land
• Temporal Scale: Last 70 years; all seasons (winter, spring, summer, fall)

Methodology and Data

• Models used: CMIP6 climate models
• Data sources: Observational data (Berkeley Earth, ERA5 reanalysis)

Main Results

• Observational data show an increase in warm spell days across all seasons over the last 70 years in Northern Hemisphere mid-latitude land.
• Mid-latitude land averages for warm spell day increases range from 0.8 days per decade in winter to 1.5 days per decade in summer, with spring trends reaching 1.3 days per decade.
• CMIP6 models underestimate the observed increase in mid-latitude averaged spring warm spell days, with a multi-model mean of 0.7 days per decade, and observational trends (1.3 days per decade) falling outside the CMIP6 model spread (0.24 to 1.11 days per decade).
• CMIP6 models overestimate fall warm spell trends, particularly relative to annual average trends, reporting trends as high as 1.17 times the annual average compared to observed 0.85 times the annual average.
• The seasonality of these trends and associated model biases is strongly controlled by seasonal mean temperature trends.
• CMIP6 biases in seasonal temperature trends are partially linked to biases in surface albedo and soil moisture changes.

Contributions

• This study extends previous research by assessing warm spell trends across all seasons, rather than focusing solely on warm-season heatwaves.
• It identifies significant seasonal biases in CMIP6 climate models regarding warm spell trends, particularly underestimation in spring and overestimation in fall.
• It links these model biases to underlying biases in seasonal mean temperature trends, and further to surface albedo and soil moisture changes, providing critical insights for improving future climate projections.

Funding

[Information not available from the abstract.]

Citation

@article{Admasu2026assessment,
  author = {Admasu, Lualawi Mareshet and White, Rachel H. and Orsi, Anaïs},
  title = {An assessment of Northern Hemisphere warm spell trends across seasons: spring warm spells increasing faster than projected},
  journal = {Environmental Research Letters},
  year = {2026},
  doi = {10.1088/1748-9326/aeb436},
  url = {https://doi.org/10.1088/1748-9326/aeb436}
}