Winter easing its grip on Northeast

Temperatures rising 0.8 degrees a decade

Dan Lambrecht, Blue Hills ski operations manager, is among those affected by milder Northeast winters. (DAVID L. RYAN/GLOBE STAFF)

The quintessential New England winter - frozen ponds, frigid days, and neighborhoods blanketed in white - is quietly fading away, as the season gets warmer and less snowy, according to an exhaustive new study.

Analyzing four decades of winter climate data, beginning in 1965, University of New Hampshire scientists found that regional temperatures are rising at a rate of 0.8 degrees per decade. Meanwhile, the number of days with snow on the ground is decreasing at the rate of 3.6 days per decade, the study found.

Both trends have intensified with time and were strongest in the heart of winter - January and February.

"A lot of people who have lived in the Northeast for 30 to 40 years have witnessed a distinct change in the character of their Northeast winter," said Elizabeth Burakowski, lead author of the study and a climate researcher at UNH. "Climate has changed in the past, and it will change in the future, but what makes this period distinct is we're witnessing this change in a human lifetime."

The study, published in October in the Journal of Geophysical Research-Atmospheres, covered a region that stretches from New Jersey to Maine. Researchers analyzed data from 123 monitoring stations that reported the presence of snow on the ground, 88 stations monitoring snowfall, and 138 stations monitoring temperature.

Other studies have shown that winters in the Northeast are warming faster than other seasons, but this work used a more rigorous analysis and also suggested a possible way in which changes in snow cover may amplify warming effects.

When the Northeast looks as it does on holiday greeting cards, covered in a pristine shell of fresh powder, it changes the way the earth absorbs heat from the sun, because white snow reflects heat away from the earth. But when there isn't snow cover, the ground absorbs the heat, which may contribute to the earth's warming.

The authors found that climate stations in northern Maine reported less warming - and hypothesized that it might be because those northerly areas are more likely to be covered in snow.

If so, that would explain "the enhanced warming we're seeing" with less snow on the ground in other areas, said study coauthor Cameron Wake, a UNH climatologist.

For now, the region is experiencing something of a weather whipsaw. Yesterday was the warmest Dec. 10 ever recorded in Portland, Maine. But with that news came a warning from the Maine Emergency Management Agency about a wintry mix of weather beginning tonight.

"This whipsaw of weather from really warm days to cold days back to warm days may in fact be an indication of the weather we're going to experience in the future, in a world warmed by greenhouse gases," Wake said.

Richard Primack, a Boston University biologist, has watched winter's icy grip loosen as he's watched the ice on skating ponds grow thinner and through his academic work. Using the observations of transcendentalist writer Henry David Thoreau from more than a century and a half ago, Primack has found the changes in Walden Pond's thaws. Today the pond typically thaws in March, or even late February, Primack said. Thoreau didn't see it thaw until late March or April.

While snow is an emblem of winter in many people's minds, it is not the best way to understand warming; the issue is really about average temperature.

"We still haven't gotten to that magical point where the freezing line is breached, and it's going to be difficult to get it to snow," said David Robinson, a professor of geography at Rutgers University. "Last winter is a wonderful example. . . . New England got clobbered last year, although it was not a cold winter."

The changing weather has variable effects for traditional winter activities.

Jim Batey, director for Somerset Economic Development Corporation in Maine, said that while snowmobiling and other snow-related activities are central to the businesses in his region, many are diversifying, with recreational all-terrain vehicle use growing as fast as snowmobiling did several decades ago.

"We had an abnormal winter three years ago, and it certainly brought home the point that if we don't have snow, that it's going to negatively impact a lot of businesses in this region," Batey said.

Chuck Henderson of North Conway, N.H., can look back over 38 years of selling outdoor apparel and see that "gradually the trend is toward shorter winters, warmer temperatures."

Warming "is definitely something people do keep on their radar; it's something we certainly have in the forefront of our thoughts," said Jen Butson, spokeswoman for the Vermont Ski Areas Association. "A lot of the ski areas are taking measures in green initiatives and trying to do their part to be green conscious."

Carolyn Y. Johnson can be reached at cjohnson@globe.com.

Correction: Because of an editing error, a secondary headline on a Page One story yesterday about winters in New England getting warmer and less snowy gave an incorrect number to describe the rate at which regional temperatures are rising. They are rising at a rate of 0.8 degrees each decade.