Why winter is getting warmer and what it means for the future

It was a wet and mild winter for most during the 2022-2023 season, with the National Oceanic and Atmospheric Administration reporting the average temperature for the contiguous U.S. this winter was 34.9 degrees Fahrenheit, or about 2.7 degrees above average.

Winter also saw about 0.90 inches of precipitation above average, which make 2023 the third wettest winter on record. However, that didn't materialize into snow for all locations.

Parts of the East Coast, including New York City, have had one of their least snowy seasons to date, NOAA reported, due to unseasonably warm temperatures throughout the region.

Massachusetts had its warmest winter on record. Connecticut, New Jersey, Maryland, Ohio, West Virginia, Virginia and Kentucky ranked second warmest while 19 additional states ranked among their top-6 warmest winter seasons of the last 128 years, according to NOAA data.

Less snow overall in the Northeast

The Northeast has experienced an increase in the proportion of winter precipitation falling as rain rather than snow. This trend is projected to continue over the 21st century with a northward shift in the snow-rain transition zone, experts said.

A 2018 study projects both a decrease in the overall frequency of Northeast snowstorms this century, as well as a greater likelihood that the heaviest snowstorms will bring more snow when temperatures do happen to be cold enough.

Tick-borne illness is on the rise

As winter gets shorter, disease-carrying pests are migrating farther north and thriving.

Ticks are moving up the eastern seaboard, already fully established in southern Massachusetts and getting into Maine. As winters continue to shrink in calendar days, the Lyme disease-carrying black-legged ticks will become established farther North, even into northern Maine.

In Maine, the total number of reported Lyme disease cases was 108 in 2001. The preliminary total cases for 2022 is 2,617, a new record, according to data from the Maine Centers for Disease Control and Prevention.

The Great Lakes aren't as icy as often

Nearly a quarter of the surface freshwater on Earth is banked within the Great Lakes, and just like our planet, the waters are warming.

Despite year-to-year variability, long-term trends show an average 22% decline in the annual maximum ice cover across all of the Great Lakes since 1973.

Less ice cover means more open-face water during the winter months and this can lead to more lake-effect precipitation. For now, that means more lake-effect snowfall coming off the lakes. As the climate continues to warm, this will lead to more lake-effect rainfall.

Overall, the Great Lakes are frozen for eight to 46 fewer days now than they were in the early 1970s, according to the Environmental Protection Agency.

On Feb. 13, near the peak of the ice season for the Great Lakes, the combined ice cover across the Great Lakes was a record low of 7.3% for that date, according to the NOAA Great Lakes Environmental Research Laboratory.

An increase in heavy lake-effect precipitation can lead to more runoff with various nutrients loading into the lakes at higher levels, leading to more favorable conditions for toxic algal blooms.

A longer growing season

The trend has become clear: the last frost of the cold season is getting earlier and the first frost in fall is getting later. Overall, the growing season in the U.S. has increased by nearly three weeks since the early 1900s, according to the EPA.

A longer growing season can be beneficial to a few crops, but overall it causes more issues than benefits.

Allergy season is getting longer and getting worse. As the growing season expands, due to a shorter winter, it means pollen is in the air longer throughout the year and in more abundance due to the extra time for more growth, experts said.

When soils don't freeze over for as long in winter, microbes will continue to eat away and lessen the organic matter in the soil, making it weaker and less nutrient dense.

A longer growing season means a higher demand for irrigation, straining water resources.

Fruit and nut trees need numerous cold winter days in order to recover from the prior season. When they don't get enough consecutive cold days they will not yield much through the coming warm season.

Invasive species

Climate change has allowed hosts of species to adapt and thrive over native ecosystems throughout the U.S. Whether it is from cheatgrass-threatening ranches in the western U.S. or from Burmese pythons growing in both number and stature in the Florida Everglades, invasive species are one of the most significant, yet often overlooked side effects of a shorter and weaker winter season.

According to a United States Geological Survey study, by 2100 pythons may live in places from Kansas City, Missouri, to Long Island, New York.

Scientists are also seeing an increased risk to waterborne pathogens, like the brain-eating amoeba, and vibrio vulnificus, a flesh-eating bacteria. While cases are still rare, they are starting to spread north.

Winters have historically killed off or slowed the reproduction of mosquitoes. With warmer and shorter winters, mosquitoes are coming out and biting sooner and lasting longer, and could lead to an increase in dengue, West Nile, and other diseases such as Zika and chikungunya.

Why is winter warming so fast?

The more greenhouse gasses in the atmosphere, such as carbon dioxide and methane, the warmer our world gets.

Globally, the fastest warming occurs in colder regions, during colder seasons and colder times of the day.

Here in the U.S., winter months are heating faster for the eastern half of the country because that is where the most vegetation is. This area has more moisture, which leads to warmer nights and aids in having warmer days.

What does the future look like?

There will still be winter, but it will be shorter and warmer.

Extreme winter weather events will still intrude with heavy snow and cold temperatures.

Snowpack will continue to go down over time.

From 1982 to 2021, the snowpack season became shorter at about 86% of the sites where snowpack was measured, according to the EPA. Across all sites, the length of the snowpack season decreased by about 18 days, on average.

A reduced snowpack has impacts to recreation, water resources, agriculture, hydropower, and wildfire season, experts said.