WASHINGTON — Some people wish summer would never end. For them, a new study has good news and bad news, at least for their grandchildren. Researchers say without taking steps to prevent climate change, summers in the Northern Hemisphere of the planet will likely span six months by the end of the century.
It may sound like an appealing prospect to lovers of beach weather and short-sleeved shirts, but a team from China concludes these changes would have serious impacts on agriculture, human health, and the environment.
“Summers are getting longer and hotter while winters shorter and warmer due to global warming,” says corresponding author and physical oceanographer Yuping Guan in a media release by the American Geophysical Union.
Throwing nature out of balance
Researchers find the four seasons arrived on time and fairly evenly in the Northern Hemisphere up until the 1950s. Since then however, the growing impact of climate change is pushing the seasons into a more irregular schedule. Guan — from the State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, and Chinese Academy of Sciences — says the shift will only get more extreme if the world does nothing to slow climate change’s effect.
“More often, I read some unseasonable weather reports, for example, false spring, or May snow, and the like,” Guan adds.
To investigate how bad things already are, researchers analyzed historical records from 1952 until 2011 on the four seasons. The team defined the beginning of summer as the start of temperatures in top 25 percent for the year. Winter was defined as the start of temperatures in the lowest 25 percent.
The results reveal that, on average, summer in Earth’s Northern Hemisphere is already two weeks longer than in the past. Researchers say the summer season has gone from 78 days in 1952 to 95 days in 2011. At the same time, winters have shrunk from 76 to 73 days.
Th other seasons are also shorter today, with spring shrinking from 124 to 115 days and fall shortening from 87 to 82 days each year. The study authors find spring and summer now begin earlier, while fall and winter start later. Over this time, the Mediterranean region and the Tibetan Plateau have experienced the greatest changes in their seasonal schedule.
According to the team’s estimates, winter will last less than two months in the year 2100.
What impact will this have on the world?
“Numerous studies have already shown that the changing seasons cause significant environmental and health risks,” Guan warns.
The study points to birds shifting their migration patterns and flowers blooming at different times as a result of changing seasonal cycles. Those changes may lead to “mismatches” between the animals and their normal food sources — further disrupting the world’s ecology.
Seasonal changes also have a dramatic impact on agriculture, as false springs and late winter snowstorms can damage budding plants. During a longer growing season, humans will likely suffer more allergy problems and disease-carrying mosquitoes will have more time to strike.
Monsoon researcher Congwen Zhu, who did not participate in the study, adds shifting seasons may also bring on more extreme weather events across the planet.
“A hotter and longer summer will suffer more frequent and intensified high-temperature events – heatwaves and wildfires,” Zhu says.
A warmer and shorter winter may lead to weather instabilities that produce cold surges and winter storms, like the ones recently battering places like Texas and Israel.
“This is a good overarching starting point for understanding the implications of seasonal change,” concludes Scott Sheridan, a climate scientist at Kent State University who did not take part in the study. “I think 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.”
The study appears in the journal Geophysical Research Letters.