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Published on: December 12, 2025
Observed changes in accumulated dangerous heat during Northern Hemisphere summers
Jennifer A Francis1, Natasa Skific2, Judah Cohen3,4
1Woodwell Climate Research Center, Falmouth, MA, USA. jfrancis@woodwellclimate.org.
Scientific Reports
|July 10, 2026
Summary
Extreme heat is the deadliest weather hazard. A new metric, the accumulated dangerous heat index, identifies regions with hazardous heat conditions, highlighting the urgent need to reduce greenhouse gas emissions.
Area of Science:
- Climatology
- Environmental Science
- Public Health
Background:
- Extreme heat is the leading cause of weather-related fatalities globally.
- Rising global temperatures due to greenhouse gas emissions are expanding areas with excessive heat.
- Some regions are becoming dangerously uninhabitable due to prolonged heat exposure.
Purpose of the Study:
- Introduce a novel metric: the accumulated dangerous heat index.
- Identify Northern Hemisphere summer regions experiencing hazardous heat conditions.
- Assess changes in heatwave magnitude and duration and their drivers.
Main Methods:
- Developed the accumulated dangerous heat index metric.
- Analyzed changes in temperature and humidity contributing to heat hazards.
- Investigated links between amplified high-latitude warming and dangerous heat.
Main Results:
- Identified specific regions in the Northern Hemisphere experiencing increased dangerous heat.
- Attributed observed heat changes to shifts in temperature and humidity.
- Found potential links to amplified warming in high-latitude land areas.
Conclusions:
- The accumulated dangerous heat index is a valuable tool for identifying heat risks.
- Findings underscore the critical need to reduce greenhouse gas emissions.
- Results will aid policymakers in preparing for future heat threats.
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