By SETH BORENSTEIN (AP Science Writer)
In much of America, including the normally cold north, winter didn't really happen this year.
In typically cold areas like Burlington, Vermont, and Portland, Maine, the temperature never dropped below zero. Minnesota even referred to the last three months as “the lost winter,” which was even warmer than the infamous “year without a winter” in 1877-1878. Michigan, where mosquitos were biting in February, provided disaster loans to businesses affected by the lack of snow. The Great Lakes saw record low winter ice levels, with Erie and Ontario being “essentially ice-free.”
From Colorado to New Jersey, and Texas to the Carolinas, spring arrived three to four weeks earlier than the 1991-2020 average, according to the National Phenology Network, which tracks the timing of plants, insects, and other natural signs of the seasons.
Yale Climate Connections meteorologist Jeff Masters said, “Long-term warming combined with El Nino conspired to make winter not show up in the U.S. this year.” Masters was surprised to be bitten by a mosquito in Michigan this year.
The National Oceanic and Atmospheric Administration confirmed on Friday that the winter of 2023-2024 was the warmest in almost 130 years of record-keeping for the United States. The Lower 48 states averaged 37.6 degrees (3.1 degrees Celsius), which is 5.4 degrees (3 degrees Celsius) above the average.
This is just the latest in a series of broken temperature records, both national and global, which scientists attribute mostly to human-caused climate change from the burning of coal, oil, and gas.
By a significant margin, this was the warmest U.S. winter. The past three months were 0.82 degrees (0.46 degrees Celsius) warmer than the previous record set eight years ago, which “is a significant increase over the previous record,” said Karin Gleason, chief of monitoring at NOAA’s National Centers for Environmental Information.
Although last month was only the third-warmest February on record, Iowa surpassed its warmest February by 2 degrees, while parts of Minnesota were 20 degrees warmer than the February average, according to Gleason.
On Feb. 11, Great Lakes ice cover reached a February record low of 2.7%.
A strong area of high pressure caused the eastern United States to be warm and dry, while California continued to experience atmospheric rivers, Gleason said.
The European climate agency Copernicus recently announced that this was the warmest winter globally, mostly due to climate change, with an additional boost from a natural El Nino, which affects weather worldwide and adds extra heat.
In the past 45 years, winter has warmed faster in the United States than it has globally, with winters in the Lower 48 states now averaging 2.2 degrees (1.2 degrees Celsius) warmer than in 1980, according to an analysis of NOAA data by The Associated Press.
This is likely because land warms up faster than the ocean, and much of the United States consists of land, while most of the globe is ocean, according to Gleason.
According to data from NOAA, the rate of additional warming in the United States has slowed down since 2000, even though the overall temperature is still increasing. Winter weather expert Judah Cohen from a company in Boston called Atmospheric Environmental Research attributes this to Arctic Amplification, which is when climate change causes the Arctic to warm much more than the rest of the world and appears to shift weather patterns farther south.
As the Arctic warms faster, the jet stream — which moves weather systems across the Earth — becomes less stable and loses strength. This causes the cold air at the top of the planet, known as the polar vortex, to break free from its usual location and move elsewhere, bringing short periods of very cold air that temporarily counteract the overall warming pattern in some places, Cohen explained.
This occurred briefly in January when winter had a short appearance in the contiguous United States, according to Cohen. However, for most of this year, when the polar vortex shifted, it affected Europe or Asia with blasts of icy air rather than the United States. As a result, there was no offsetting impact on winter temperatures in the U.S., he stated.
Boston did not experience extremely low temperatures this year, with the lowest winter temperature being 14 degrees, which set a record for the absence of severe cold.
And snow? Not much, at least in the eastern and northern regions.
In Fort Kent, located in far northern Maine, a lack of snow led to the cancellation of an annual dog sled race. The town had received 46.8 inches (119 cm) of snow this year as of last week, slightly more than half of the usual amount, according to the National Weather Service.
In February, snow cover in the United States was the second lowest on record, and in December, it was the third lowest. Only January had more snow cover than normal, as reported by the Rutgers Snow Lab.
According to Theresa Crimmins, the director of the National Phenology Network, warm winters have consequences.
“Warm winters can also lead to earlier, longer, and more abundant pest seasons, as populations were not reduced by the cold,” Crimmins stated in an email. “Additionally, the allergy season can be worse, starting earlier, lasting longer, and resulting in more pollen in the air.”
Due to the warmer weather, trees and flowers may bloom earlier. The cherry blossoms in Washington are expected to reach their peak about two weeks earlier than they did in 2013. Early blossoms can disrupt the delicate timing with pollinators and birds.
“Many of the birds that migrate south for the winter use day length as a signal to return north in the spring,” Crimmins said. “In years like this one, where plant and insect activity starts much earlier than usual, the birds can miss the peak availability of food by arriving too late.”
However, there is some positive news for California, with atmospheric rivers and snowstorms expected to replenish snowpacks and fill reservoirs that were dangerously low until a couple of years ago, according to Gleason.
Winter weather expert Cohen, who is located outside of Boston, jokingly remarked that the U.S. now has only two seasons: “We have summer and we have November.”
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Associated Press writer Patrick Whittle contributed from Portland, Maine.
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For more of AP’s climate coverage, visit http://www.apnews.com/climate-and-environment
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Follow Seth Borenstein on X at @borenbears
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