Record-shattering March temperatures in Western North America virtually impossible without climate change

The report analyzes a record-shattering heatwave in the southwestern United States and northern Mexico in March 2026, finding that such an event would have been virtually impossible without anthropogenic climate change. Using a combination of observation-based data and climate models, the study estimates that the intensity of 1-in-100-year March heat events has increased by 2.6°C and their likelihood has increased by a factor of approximately 800. The document highlights the extreme vulnerability of non-acclimatized populations and the risk of accelerated snowmelt in the Sierra Nevada and Colorado mountains.

• The March 2026 heatwave in western North America is an extremely rare event; in the current climate, it is expected to occur only once every 500 years, though the study uses a benchmark return period of 100 years for its analysis to avoid overestimating extremeness.
• Combining climate models and observation-based evidence, the study finds that the intensity of such heat events has increased by an estimated 2.6°C and the likelihood has increased by a factor of about 800, concluding the event would be virtually impossible without human-induced climate change.
• Analysis of the last 10 years (during which the world warmed by approximately 0.4°C) shows a rapid increase in heat extremes, with intensity increasing by 0.8°C and likelihood increasing by a factor of about 4.
• While warming is evident across all months in the region, the most substantial warming signal for heat extremes occurs in March, where current temperatures can be up to 6°C higher than in a baseline climate that was 1.3°C cooler.
• The heatwave is expected to cause rapid snowmelt in the Sierra Nevada region of California and the mountains of Colorado, where snowpack levels are already at their lowest since 1981, potentially increasing water shortages and wildfire danger.
• The event poses a severe public health risk because it occurs early in the season when populations, including tourists and migrants, are not yet acclimatized to high temperatures.

APA

Clarke, B., Keeping, T., Zachariah, M., Barnes, C., Mitra, S., Vahlberg, M., Pinto, I., Bergin, C., Philip, S., & Arrighi, J. (2026). Record-shattering March temperatures in Western North America virtually impossible without climate change. World Weather Attribution. https://www.worldweatherattribution.org/record-shattering-march-temperatures-in-western-north-america-virtually-impossible-without-climate-change/

Chicago

Clarke, Ben, Theodore Keeping, Mariam Zachariah, Clair Barnes, Spandita Mitra, Maja Vahlberg, Izidine Pinto, et al. Record-shattering March temperatures in Western North America virtually impossible without climate change. World Weather Attribution, 2026. https://www.worldweatherattribution.org/record-shattering-march-temperatures-in-western-north-america-virtually-impossible-without-climate-change/.

Wikipedia

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BibTeX

@techreport{clarke2026recordshattering, author = {Clarke, Ben and Keeping, Theodore and Zachariah, Mariam and Barnes, Clair and Mitra, Spandita and Vahlberg, Maja and Pinto, Izidine and Bergin, Claire and Philip, Sjoukje and Arrighi, Julie}, title = {{Record-shattering March temperatures in Western North America virtually impossible without climate change}}, institution = {World Weather Attribution}, year = {2026}, month = mar, url = {https://www.worldweatherattribution.org/record-shattering-march-temperatures-in-western-north-america-virtually-impossible-without-climate-change/}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }