Summers across North America and Europe have expanded by roughly 30 days since the 1960s, with inland areas gaining more than six extra summer days per decade since 1990.
University of British Columbia researchers analyzed global temperature data from 1961 to 2023, defining summer as periods when daily temperatures exceeded locally-calculated thresholds rather than using fixed calendar dates. The study found summer heat accumulation is growing three times faster than the 1961-1990 baseline period.
Sydney gains nearly 15 extra summer days per decade, while Minneapolis adds 9 days and Tokyo only 2.
Ocean areas are changing fastest because water temperatures don’t fluctuate as dramatically as land.
Researchers noted summers now arrive and end more abruptly, leaving less time for ecosystems and infrastructure to adapt.