Summer is getting longer, and it’s happening faster than we thought

New research finds summers are expanding 50 per cent faster in many areas than previously reported, with quicker transitions between seasons.

Peer-Reviewed Publication

University of British Columbia

News Release 8-Apr-2026

Summer weather is arriving earlier, lasting longer and packing more heat than it used to—and it’s happening faster than scientists had previously measured.

A new study by UBC researchers has found that between 1990 and 2023, the average summer between the tropics and the polar circles grew about six days longer per decade. That’s up from roughly four days per decade found in past research investigating up until the early 2010s.

For many cities, the numbers are even more striking. In Sydney, Australia, summer temperatures now last about 130 days, up from 80 days in 1990, adding 15 days per decade. Toronto summers are expanding by eight days per decade.

The researchers didn’t use the calendar definition of summer (June through August in the Northern Hemisphere and December through February in the Southern Hemisphere). Instead, they defined summer based on the weather: the stretch of days each year when temperatures rise above what was historically typical for a given location during the warmest part of the year—a threshold set using climate data from 1961 to 1990.

The study’s findings have implications for agriculture, water supply, public health and energy systems, many of which have been built around assumptions about when the warm season begins and ends.

“These findings challenge what we believe to be the normal cycle of the seasons,” said lead author Ted Scott, a PhD student in UBC’s department of geography. “When summer happens and how quickly it arrives impact patterns and behaviours in plant and animal life, and human society.”

Seasons are changing gears more quickly

The study also found that seasonal transitions—the shift from spring to summer and from summer to autumn—are becoming more abrupt. Instead of a gradual warm-up, summer-like temperatures arrive more suddenly. This could disrupt systems that depend on seasonal cues; for example, flowers may bloom before pollinators are active, crops may need to be planted earlier, and rapid spring warming may lead to faster snowmelt and greater spring flood risk.

“The changes may be very disruptive to a wide range of systems,” Scott said. “An expectation in the Northern Hemisphere that June is when summer starts may be ingrained in planning and policy, meaning we could be ill-prepared for earlier heat.”

The heat is adding up—faster than before

The study, published Tuesday in the journal Environmental Research Letters, also introduces a new way of measuring cumulative heat that builds up over a summer, combining temperature and time. By this measure, accumulated summer heat over Northern Hemisphere land is rising more than three times faster since 1990 than it did from 1961 to 1990.

The study found that coastal areas in the Northern Hemisphere are seeing some of the fastest growth in summer length and accumulated heat, which could affect millions of people who have moved to these areas in part because of their perceived moderate climate.

Scott and co-authors Dr. Rachel White, professor in the department of earth, ocean, and atmospheric sciences and Dr. Simon Donner, professor in the department of geography and the Institute for Resources, Environment and Sustainability, analyzed temperature data spanning 1961 to 2023 across land, ocean and coastal zones in both hemispheres, and examined trends in 10 cities around the world.

The research points to urgent questions for future study: How will longer, faster-transitioning summers affect the timing of extreme weather events? What will earlier spring heat mean for food supply, given that growing seasons are shifting but daylight—a key driver of plant growth—is not? And do today’s climate models that inform planning and policy fully capture these trends or do they need updating?

For now, the study makes tangible what many people may have sensed—that the rhythm of the year is changing, and that this change is happening faster than most of us realized.