6 months of summer could be the norm by 2100, study finds

A man watches California wildfire smoke blot the sky in September 2020.
A man watches California wildfire smoke blot the sky in September 2020. Longer summers mean longer wildfire seasons, more heatwaves and extreme storms. (Image credit: Getty)

Global warming will change the lengths of the four seasons, a new study suggests, potentially making six-month-long summers the norm in the Northern Hemisphere by the year 2100.

In contrast, winters could last less than two months a year, while spring and autumn similarly shorter. These drastic seasonal changes would have wide-reaching impacts on the world, disturbing agriculture and animal behavior, increasing the frequency of heat waves, storms and wildfires, and ultimately posing "increased risks to humanity," the study authors wrote.

"Tropical mosquitoes carrying viruses are likely to expand northward and bring about explosive outbreaks during longer and hotter summers," the researchers wrote in their study, published Feb. 19 in the journal Geophysical Research Letters.

Related: 10 Steamy signs that climate change is speeding up

These and other potential impacts "heighten the urgency of understanding" how the seasons morph with climate change, and whether that transformation will continue in the future.

To find out, the study authors looked at historical daily temperature data from 1952 to 2011 in the Northern Hemisphere. Specifically, they wanted to see how the onset of new seasons changed from year to year. The team defined the start of summer as the onset of temperatures in the hottest 25% of temperatures, averaged from 1952 to 2011. They defined winter as the start of temperatures in the coldest 25% from the same period, while autumn and spring were in between.

The researchers found that, on average, summer lengthened from 78 to 95 days between 1952 and 2011. Meanwhile, winter shrank from 76 to 73 days. The transition seasons shrank as well, with spring shortening from 124 to 115 days and autumn from 87 to 82 days. Average temperatures changed accordingly during this period; summer and winter both became warmer.

The team also used climate models to predict how much the seasons are likely to change in the future. Under the business-as-usual scenario (that is, if no efforts are made to mitigate global warming), spring and summer will start a month earlier in 2100 than they did in 2011, while fall and winter will start half a month later. As a result, the Northern Hemisphere will spend more than half the year in summer — and average summer temperatures are only expected to rise.

This seasonal shift would impact everything from when birds migrate to when crops grow, touching virtually every aspect of Earth's biosphere, the team wrote. Preventing the most jarring changes to our planet's seasons in the future begins with drastically reducing carbon emissions now.

Originally published on Live Science.

Brandon Specktor

Brandon is the space/physics editor at Live Science. His writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.