TORONTO -- A new study has found that summers in the Northern Hemisphere may last nearly six months by 2100, if efforts to combat climate change are not taken.

Researchers behind the study out of China warn that a longer summer season will likely have "far-reaching impacts" on agriculture, human health, and the environment.

The study, published Monday in peer-reviewed scientific journal Geophysical Research Letters, reports that global warming is driving "dramatic and irregular" changes to the length and start dates of seasons, which may become more extreme in the future without efforts to mitigate climate change.

"Summers are getting longer and hotter while winters shorter and warmer due to global warming," Yuping Guan, lead author and physical oceanographer at the Chinese Academy of Sciences, said in a press release.

According to the study, the researchers used historical daily climate data from 1952 to 2011 to measure changes in the four seasons’ length and onset in the Northern Hemisphere.

The study defines the start of summer as the onset of temperatures in the hottest 25 per cent during that time period. Winter, as defined in the report, is the onset of temperatures in the coldest 25 per cent.

The team then used climate change modelling data to predict how seasons will shift in the future.

The study found that summer extended from 78 to 95 days on average between 1952 to 2011, while winter shrank from 76 to 73 days. According to the study, spring and fall also shrank, from 124 to 115 days and 87 to 82 days, respectively.

The study also reported that spring and summer began earlier, while fall and winter started later. The Mediterranean region and the Tibetan Plateau experienced the greatest changes to their seasonal cycles, according to the report.

If these trends continue without any effort to lessen the effects of climate change, the authors predict that winter will last less than two months, and spring as well as fall will contract further by 2100.


Studies have already shown that changes in the length of the seasons can cause significant environmental and health risks, including birds shifting their migration patterns and plants flowering at different times.

According to the study, these "phenological changes can create mismatches" between animals and their food sources, disrupting ecological communities. Researchers noted that seasonal changes can create issues for agriculture when a false spring or late snowstorm damages budding plants.

With longer growing seasons, the study reported that humans will breathe in more allergy-causing pollen, while disease-carrying mosquitoes will be able to travel and survive farther north.

Congwen Zhu, a monsoon researcher at the Chinese Academy of Meteorological Sciences, said this shift in seasons may also result in more severe weather events.

Zhu, who was not involved in the study, said in the release that a hotter, longer summer will cause more "frequent and intensified high-temperature events" including heatwaves and wildfires.

Zhu added that warmer, shorter winters may also cause weather instability that leads to cold surges and major winter storms, much like February's snowstorm in Texas.

Scott Sheridan, a climate scientist at Kent State University who was not a part of the study, said these extreme weather events are a "good overarching starting point" in understanding the implications of climate change on the seasons.

While Sheridan acknowledged that it is difficult to conceptualize a two or five degree yearly increase in temperature, he said "realizing that these changes will force potentially dramatic shifts in seasons probably has a much greater impact on how you perceive what climate change is doing."