In the U.S., temperatures were above average across the country during 2022's winter months. This has scientists wondering: are summers getting longer? Are the seasons shifting? And is it possible that it could be 75 degrees and sunny even during winter in the future?

In a recent study published in the Geophysical Research Letters, researchers looked at seasons in the Northern Hemisphere between 1952 and 2011. They found evidence to suggest that the length of the four seasons has changed due to global warming — and so have each season's temperatures. Let's take a look at some of the most important conclusions from this research and how these changes may impact the future of life on Earth.

The Four Seasons No Longer Have Equal Amounts of Months

Before climate change started significantly altering our environment, a single year could traditionally be separated into four equal seasons: spring, summer, fall and winter, each of which lasted about three months. Today, that's no longer the case. In the Northern Hemisphere, the four seasons don't have an equal amount of months anymore. In the time period between 1952 and 2011, the length of summer in the Northern Hemisphere has increased, while the length of spring, autumn and winter has decreased.

Are the seasons shifting? In short, yes. A year can no longer be divided into four equal-length seasons, and research suggests the seasons will continue to shift even more over time.

Summers Start Earlier

Are summers getting longer? Yes, scientists have also found that summers have been starting earlier, lengthening the season.

For every 10 years from 1952 to 2011, summer started 1.6 days earlier and lasted 4.2 days longer. In the last half-century alone, the length of summer in the Northern Hemisphere has increased from 78 to 95 days. These extended summer seasons have translated into hotter summers. From May to September, the frequency, duration and cumulative heat of heatwaves have increased significantly since the 1950s.

Winters, Springs and Autumns Are Shorter

Researchers have also discovered that the winters, springs and autumns are getting shorter. In the same time period between 1952 and 2011, the spring season decreased from 124 to 115 days, autumn went from 87 to 82 days and winter shrank from 76 to 73 days.

These shorter winters, springs and autumns are due to a shift in the onset of these seasons and another shift in their withdrawals. The study found that spring started earlier by 1.6 days every 10 years and summer started 2.5 days earlier. Autumn was delayed by 1.7 days every 10 years, and winter was delayed by 0.5 days.

Temperatures Have Also Changed

Along with the timing of the seasons, seasonal temperatures have also changed: Summers have gotten longer and hotter, but winters have become warmer, too. The warming trend of winter was most pronounced in northern North America, where the temperature has risen at the rate of more than 0.4 °C every 10 years. Shorter, warmer spring and autumn seasons have become the new normal.

The Trend in Changing Seasons May Be Amplified in the Future

Even if the current warming rate does not accelerate, changes in seasons will still be exacerbated in the future. By the end of this century, spring and summer may start about a month earlier, while autumn and winter may start about half a month later. By 2100, summers may last nearly half the year, and there may be less than two months of winter.

How will these changes affect humanity? Scientists predict that longer summers will likely disturb agriculture seasons and the rhythm of species' activities. This includes early flowering of plants and early bird migrations, which could disrupt the structure and function of ecological communities.

Warmer winters may also have an impact on crop yields. The insufficient chilling demand for bud dormancy due to milder winters can stunt the growth of plants, resulting in reduced yields and quality. Longer summers may also cause more frequent heat waves, more extreme storms and longer wildfire seasons.

Changes to Earth's Seasons Carry Risk to Human Health

Longer, more intense summers may also impact human health. The extension of the growing season may cause more allergenic pollen and longer allergy periods. During longer and hotter summers, tropical mosquitoes carrying viruses will likely expand northward and bring about explosive outbreaks.

Groups who work outdoors or indoors without cooling systems will face severe heat exhaustion. Higher temperatures are also correlated with a higher prevalence of mental health issues, and shorter winter periods may cause higher crime rates across several regions of the U.S.

While the seasons may be shifting due to human-accelerated climate change, there is still hope for the future. Organizations around the world are developing advanced technologies and new solutions to combat climate change. Even so, it's up to everyone to do their part to help maintain the environment — and in the meantime, you might want to keep the T-shirts out for winter next year.

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