The frequency of dangerous humid heat days has significantly surged since the 1970s, with climate change being the primary catalyst. As a result, many areas worldwide are experiencing unprecedented risks related to heat-related illnesses, prompting a deeper examination of this growing global challenge.
Global Increase in Dangerous Humid Heat Days
Since the 1970s, the number of days characterized by dangerous levels of humid heat has more than doubled globally. A “dangerous humid heat day” is defined by a daily maximum wet-bulb temperature of 25°C (77°F) or higher, a threshold determined by studies indicating significant impacts on core body temperatures.
On a global scale, these conditions have increased from an average of 10 days per year in the 1970s to 23 days per year in the past decade (2016-2025). Climate Central’s recent report, Global Analysis: Dangerous Humid Heat Rising Due to Climate Change, highlights these escalating global risks.
Impact in the United States
In the United States, the prevalence of dangerous humid heat days has also risen sharply. From an average of 10 days per year in the 1970s, these days have increased to 21 per year in the last decade. Notably, human-induced climate change is responsible for 62% of these occurrences, up from 10% in the 1970s.
The South and Southeast regions, including cities in Texas, Louisiana, Florida, and San Juan, Puerto Rico, now experience the highest number of these days. Some Gulf Coast areas report over 100 dangerous humid heat days annually. Furthermore, the Upper Midwest, Ohio Valley, and Northeast have seen an emergence of these conditions, where they were previously rare.
Expanding Risks Across the U.S.
Climate change has expanded the footprint of humid heat risks across the nation. Twenty-five U.S. cities that experienced zero dangerous humid heat days per year in the 1970s now report at least one annually. This shift highlights the growing influence of climate change on regional weather patterns.
Understanding the Science
Humid heat, a combination of high temperatures and humidity, impairs the body’s ability to cool itself through sweating, leading to severe health risks. Older adults and individuals lacking access to cooling are particularly vulnerable. For further details, refer to Humid Heat: A Growing Health Risk in a Warming Climate.
Local and Global Analysis Tools
Climate Central’s Climate Shift Index: Humid Heat tool enables users to explore the impact of climate change on humid heat on a daily basis. The tool provides data on regions experiencing dangerous humid heat due to human activities. Users can share custom maps and access expert discussions through webinars and FAQs.
For a deeper understanding of the methodologies behind these findings, access the full report, Global Analysis: Dangerous Humid Heat Rising Due to Climate Change.
Original Story at www.climatecentral.org