How Warming Winters Are Affecting Everything
Winters are warming faster than other seasons across much of the United States. While that may sound like a welcome change for those bundled in scarves and hats, it's causing a cascade of unpredictable impacts in communities across the country.
Temperatures continue to steadily rise around the globe, but that trend isn't spread evenly across the map or even the yearly calendar.
"The cold seasons are warming faster than the warm seasons," says Deke Arndt, chief of climate monitoring at the National Oceanic and Atmospheric Administration's National Centers for Environmental Information. "The colder times of day are warming faster than warmer times of day. And the colder places are warming faster than the warmer places."
In the U.S., that means winters in both Maine and Alaska are around 5 degrees Fahrenheit hotter on average since the early 1900s. One reason: The snowpack, which is a good reflector of sunlight, is melting earlier in the season. With fewer days of snow cover, sunlight is absorbed into the ground and warms the surrounding area.
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Still, winter warming can be seen almost everywhere. January 2020 was the Earth's hottest recorded January on average, compared with 141 years of temperature records. The four warmest Januaries have all occurred since 2016.
"Those changes are big," Arndt says. "We're not just watching numbers. We're watching changes in real people's real lives."
Here are some of those changes happening around the country.
The nation's largest economy and largest agricultural industry is heavily reliant on snow that falls high in the Sierra Nevada, which acts like a giant reservoir. The snowpack lasts through the winter and melts in late spring and early summer, sending a steady supply of water to farms and cities when they need it most.
But with warming temperatures, California's snowpack is shrinking, both because of increased snowmelt and because more precipitation is falling as rain instead of snow. Across the West, snowpack has already shrunk by 15% to 30%.
"That can have profound ramifications, west of the Rockies especially, when the timing of snowmelt is really important to how we operate reservoirs and share water with each other," says Arndt, of NOAA.
With runoff flowing earlier in the year, California's reservoirs may not be able to capture enough to supply the state during the long dry summer. For one thing, reservoirs can't be kept completely full during winter because they might be overwhelmed by floodwaters. And when warmer winter storms cause rain to fall on top of California's snowpack, it dramatically increases the risk of devastating floods.
Warmer winters are also affecting the fruits and vegetables that California sends around the country. The state produces the majority of the country's supply of almonds, wine grapes, walnuts, pistachios and peaches. But many of those crops require a certain amount of cold weather, what's known as "chill hours." Without that, pollination can be delayed or incomplete, reducing the crop that farmers get at harvest time.
"Now with the weather changing, it's becoming more of a challenge to get those chill hours," says Jonathan Battig, a farm manager for pistachios and walnuts in Arbuckle, California.
According to one study, cold temperatures that many orchard crops need could decrease by as much as 60% in California's Central Valley by 2100. Apples, cherries and pears, which require the longest period of cold weather, could be hit the hardest. That has many in the agricultural industry looking for ways to adapt, whether it's breeding more heat-tolerant trees or finding chemicals that can help trees bloom on a predictable schedule, even when the winter weather is anything but.
For decades, the Southeast actually got cooler while the rest of the country warmed. But now it's warming too, and that includes winters, with the length of the freeze-free season increasing in some places by as much as a week and a half.
That's a problem for farmers, who need cold temperatures for their plants to set fruit. The winter of 2016-2017 was too warm for Georgia peaches, for instance, and about 80% of the crop failed.
Blueberries — a bigger crop in the Peach State than peaches are — also struggle.
"When you talk to blueberry producers and peach producers, they're definitely looking at new hybrids that are more welcoming to low chill hours and different kinds of weather patterns," says Pam Knox, an agricultural climatologist at the University of Georgia.
An unusually warm January in Atlanta has also been a headache for beekeepers. If it's not cold enough, honeybees fly out of their hives and queens might start laying eggs. As they expend energy, the bees eat more of the honey they stored for the winter. If their calendar gets too out of whack from the blooms they need for nectar, they risk starvation.
And then there are the mosquitoes that can carry vector-borne diseases. Different species have different needs, but in general, cold winter temperatures kill them or slow down their reproduction cycles.
"Warmer winters will result in, usually, earlier emergence of adult mosquitoes, for example, that bite us earlier in the springtime. It means that larger populations will survive throughout the winter," says Duke University professor Bill Pan, who studies environmental change and disease.
It's already warm enough in the South for the mosquito species that can carry dengue, chikungunya and Zika. In some parts of Florida, the mosquitoes can be active year-round. According to the latest National Climate Assessment, dengue cases could go up across the Southeast in the summer, and West Nile will likely increase too.
In Maine, skiing, snowmobiling and ice fishing are an important part of the winter economy. Greg Sweetser, of the Ski Maine Association, says ski areas are preparing for climate change by expanding into summer businesses, such as mountain biking.
"It's an insurance policy to some degree," he says. "The climate is changing, it's unclear how incremental the change will be, so ski areas are being proactive."
Ice fishing is already seeing days shaved off its season in southern Maine, because the window for when lakes freeze over is shortening, says Mark Latti of the state's Department of Inland Fisheries and Wildlife. And one of Maine's largest lakes, Sebago, used to freeze over every other year, he says. "Now it's once every three years or so."
Warmer winters have also helped fuel the expansion of a pest that affects outdoor enthusiasts throughout the year: ticks.
Deer ticks transmit several diseases, including Lyme, which has grown from a few hundred cases in Maine more than a decade ago to a high last year of more than 2,100. Cases of another tick-borne disease, anaplasmosis, have also surged in the state to more than 680, up from just single cases in the early 2000s.
Deer ticks first appeared in southern Maine in the mid-1980s, but researchers at the Maine Medical Center Research Institute's Lyme and Vector-Borne Disease Laboratory say their range now extends to the northern reaches of the state.
"It's still colder than the southern tier," staff scientist Susan Elias says. "But it has been warming relatively faster. And so that's going to be helpful to ticks."
Vector ecologist Chuck Lubelczyk says warmer winters also help create a more hospitable climate for other species and the diseases they carry. The lone star tick has already been found in Maine, dropped by migratory birds from the south. Historically, it hasn't been able to survive the winter, but that's changing.
"This tick is slowly moving its way up the Eastern Seaboard," Lubelczyk says, and is now established in southeastern Massachusetts. "If it does arrive and gets established in Maine," he says, it will be "a game-changer, because it is highly aggressive."
Despite the occasional polar vortex that can send temperatures plunging well below zero, generally warmer Midwest winters have implications from agriculture to recreation.
"We talk about this all the time," says Dennis Todey, director of the U.S. Department of Agriculture's Midwest Climate Hub, in Ames, Iowa.
Freezing stops the microbes in soil from breaking down organic matter. Todey says that this contributes to the quality of Iowa's dark, rich cropland. Soils father south, where it's warmer, lose organic matter because bacteria, fungi and other critters keep munching through it all winter long.
Todey says another problem is when the temperature warms after a hard frost and then rain falls onto frozen ground. That's bad because it can cause soil to wash away.
A freeze can also help protect future crops.
"There are certain pests and diseases that cannot survive cold temperatures. They simply die off," says Rick Cruse, a soil scientist at Iowa State University. But "as the temperature warms, there's more of those that survive."
Warm winters are even worse for certain fruit and nut trees, which require chill hours during the winter. If they don't get enough of those, they won't produce the following season.
Michigan's have struggled with erratic winter weather. And the repeated freeze-thaw cycles of the 2018-2019 winter, among other weather anomalies, destroyed Iowa's chestnut crop last year.
Peter Boulay of the Minnesota State Climatology Office says warming can also be a challenge for ice fishing, a sport that draws thousands of anglers.
He says some Minnesota lakes froze up early last fall, but then a mid-November warming compromised the ice. Heavy snow on top of that led to slushy conditions that aren't conducive to safe fishing. Then January brought some nights with overnight lows as much as 10 degrees above normal.
Some Minnesotans are cutting the season short.
But Boulay says where there is solid ice, temperatures in the 20s or even 30s can be welcome. "It's not very comfortable sitting on a bucket when it's below zero."
The most visible impact of warming winters in the Mountain West is on the forests. Millions of trees have died from pine, spruce and pinyon ips bark beetles over the past three decades.
Normally, bark beetles die off in freezing temperatures. "When you have periods of temperature that do not reach the lethal level for the insects, that's when you start seeing increased survival of the population," says Jose Negron, a research entomologist with the U.S. Forest Service.
Warmer temperatures and record-low precipitation can also make trees more susceptible to infestation. The most damaged areas are in and around Rocky Mountain National Park and parts of the San Juan Mountains, the West Elk Mountains and the Sawatch Range.
"Forty to 50 percent of the mature spruce in the state has been killed during the epidemic," says Seth Davis, an assistant professor of forestry at Colorado State University. Davis' recent study found that warmer winter temperatures meant slightly bigger spruce beetles that emerged earlier and flew around longer.
While beetle outbreaks of this size have happened in the past, warmer temperatures might have an impact on their frequency. The impacts are complex, says Davis, but not necessarily all negative. Fewer trees mean more light reaches the forest floor, where flowers now grow. His research finds this is benefiting bee populations.
Another noticeable impact of warmer winters is on the region's important ski industry.
"Thanksgiving was a relatively dependable ski time, and that's not true anymore," says Jim White, a professor at the University of Colorado. As fall lasts longer and spring comes earlier, "the natural snow is not as abundant," he says, and resorts lose valuable days to make their own. What's more, he says, "the longer-term trend is for less and less snow."
Ski areas at lower elevations, as in California, feel these changes the most. "They're the ones that are going to be seeing, really, a loss of skiing altogether in 50 years or more," White says.
Colorado is lucky to have some of the highest elevations for skiing in the United States. Despite an overall warm winter, this year's snowpack is great for skiing. But White says even higher-elevation resorts are vulnerable to big changes as climate models project increasingly warmer temperatures.
Bats in December. Bluebonnets in January. Butterflies in February.
The first two months of winter in Austin, Texas, were the second warmest in 122 years of records, according to Victor Murphy, climate service program manager with the National Weather Service, and that's upsetting some rhythms of the natural world.
December and January were 4.7 degrees warmer than the 30-year average, he says, and only one night — Dec. 19 — dipped down to freezing. "That's quite a bit of warmth spread over quite a few days," says Murphy. "It's pretty significant."
In recent years, warmer winters have caused Texas' famed bluebonnet wildflowers to appear months before people expect to see them.
The climate shift also allows migrating monarch butterflies to survive in Texas later than usual.
"In cold winters, they'll have two or three sightings along the Gulf," says Chip Taylor, director of Monarch Watch. In a warm year, "you'll get butterflies that are sighted from Florida all the way to over to the middle of Texas and even into the San Antonio, Austin area."
The great migration of monarchs to Mexico already faces many pressures. Taylor thinks that continued warming during their breeding season and migration and over the winter may one day help end it altogether, leaving small "islands" of nonmigrating butterflies around the Gulf Coast.
Then there are the Mexican free-tailed bats that gather each year outside San Antonio, one of the world's largest bat colonies. They're also a nightly summer tourist attraction in downtown Austin.
"They shouldn't be here," says Austin wildlife officer Sarah Whitson. Most bats usually migrate to Mexico or become inactive in the fall, but she says more have stuck around longer the last several winters.
"It's great if there's food sources here throughout the winter," she says. But she worries what could become of the bats if a sudden cold snap kills off the bugs they eat.
Bats play a key role in agriculture, helping to control pests and to fertilize and pollinate some crops. Changing migration patterns could also hurt crops that depend on them, creating what scientists call a "mismatch."
Researchers are seeing more mismatches as a result of climate change, says Norma Fowler, a biology professor at the University of Texas at Austin. "You can get plants that bloom before the pollinators are available," she says. "You can get birds that come north before the insects are out for them to eat."
On Alaska's western coast, thick winter sea ice has long protected remote villages from storms. But that ice cover has been freezing later and shrinking to record lows, allowing strong waves to eat away at land made fragile by thawing permafrost. After years of struggle, the village of Newtok late last year started moving residents to safer ground farther inland.
Inupiat on Alaska's North Slope use sea ice as a platform from which to hunt bowhead whales and walruses. Diminished ice in the Arctic is making those harvests more difficult.
Poor ice formation is also making it riskier for Alaskans who rely on ice roads, built on some of the state's rural rivers during winter, to move freight and other goods. In recent years, residents have blamed warm temperatures for the deaths of a number of people whose snowmobiles or all-terrain vehicles fell through thin ice.
The state's oil industry needs hundreds of miles of ice roads over land for its operations, which are specially designed for freezing conditions. Companies are investing in technology to help them cope with steadily shrinking winters.
Alaska had an unusually cold January this year, but the state is warming twice as fast as the global average. In Anchorage, a city defined by its winters, this means residents are recalibrating their relationship with the coldest season.
The winter started off warm, disappointing cross-country skiers who can normally use dozens of miles of trails in the city's parks. At a major high school race in December, skiers competed on a mile-long stretch of man-made snow that wound through grass and ice.
"Normal now is kind of like this," said fourth-place finisher Max Beiergrohslein. "On again, off again, there is snow and then there isn't."
Alaska scientists are researching midwinter temperature swings, trying to track how much of a change there has been in what are known as "rain on snow" events, which create ice. Amid a particularly slick start to this winter, one Anchorage elementary school principal suggested that students wear helmets to recess, to protect them from falls on an icy playground.
Meanwhile, winter activities that require less snow, like fat-tire bicycling and ice skating on wilderness lakes, are gaining popularity.
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This report is a collaboration among NPR, Alaska's Energy Desk, Colorado Public Radio, KUT Austin, Iowa Public Radio, Maine Public Radio and WABE Atlanta.
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