Northern hemisphere summers could last almost half of the year by 2100

Without efforts to mitigate climate change, summers of nearly six months could become the new normal by 2100 in the northern hemisphere, according to a new study. According to the study’s authors, the change would likely have significant effects on agriculture, human health and the environment.

In the 1950s, in the northern hemisphere, the four seasons arrived in a predictable and fairly uniform pattern. But climate change is now causing dramatic and irregular changes in the length and start dates of seasons, which could become more extreme in the future under a business as usual climate scenario.

“Summers are getting longer and hotter while winters are getting shorter and warmer due to global warming,” said Yuping Guan, physical oceanographer at the State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, and lead author of the new study in Geophysical research letters.

Guan was inspired to study changes in the seasonal cycle while mentoring an undergraduate student, co-author Jiamin Wang. “Most often, I read non-seasonal weather reports, for example, false spring or May snow, etc.,” Guan said.

The researchers used historical daily climate data from 1952 to 2011 to measure changes in the length and onset of the four seasons in the northern hemisphere. They defined the start of summer as the onset of temperatures in the hottest 25% during this time, while winter began with temperatures in the coldest 25%. Then the team used established climate change models to predict how the seasons will change in the future.

The new study found that, on average, summer fell from 78 to 95 days between 1952 and 2011, while winter fell from 76 to 73 days. Spring and fall also contracted 124-115 days and 87-82 days, respectively. As a result, spring and summer started earlier, while fall and winter started later. The Mediterranean region and the Tibetan plateau have experienced the greatest changes in their seasonal cycles.

If these trends continue without any effort to mitigate climate change, researchers predict that by 2100, winter will last less than two months and the transitional seasons of spring and fall will narrow even further.

“Numerous studies have already shown that seasonal changes cause significant environmental and health risks,” Guan said. For example, birds change their migration patterns and plants emerge and flower at different times. These phenological changes can create mismatches between animals and their food sources, disrupting ecological communities.

Seasonal changes can also wreak havoc on agriculture, especially when false springs or late snowstorms damage budding plants. And with longer growing seasons, humans will breathe more allergy-causing pollen, and disease-carrying mosquitoes can expand their range north.

Go to extremes

This change of seasons can lead to more severe weather events, said Congwen Zhu, monsoon researcher at the State Key Laboratory of Severe Weather and Institute of Climate System, Chinese Academy of Meteorological Sciences, Beijing, who did not participate in the new study. .

“A hotter and longer summer will suffer from more frequent and intensified high temperature events – heat waves and forest fires,” Zhu said. Additionally, warmer and shorter winters can cause instability that leads to cold waves and winter storms, just like recent snowstorms in Texas and Israel, he said.

“It’s a good overall starting point for understanding the implications of seasonal change,” said Scott Sheridan, a climatologist at Kent State University who was not part of the new study.

It’s hard to conceptualize an average temperature increase of 2 or 5 degrees, he said, but “I think realizing that these changes will lead to potentially dramatic seasonal changes probably has a much bigger impact. on how you perceive what climate change is doing. ”