Fifteen years have passed since the Blizzard of '78, when students used the stone slabs flanking Widener as ski jumps and food service workers remained snowbound in the Union for three days; when the snow was so deep that even the ghosts were driven from the Yard.

Since then, Cambridge has endured periodic snowfall; but both residents and weather experts alike perceive a change in the nature of winters here. Snow and ice have yielded to slush, and once-bitter cold has eased.

The 80s and 90s have seen nothing like the storm of 1978. For the first time in Harvard's history, the University officially closed. Only emergency vehicles were allowed on the road. The city was silent. The Square shut down and students were stuck in their rooms.

"It was an extraordinary feeling of isolation...if you're going to butcher your roommates you're going to do it under those circumstances," says W.C. Burriss Young '55, associate dean of first-year students.

Orchard Professor of the History of Landscape John R. Stilgoe, who lectures about the seasonal effects of winter on the environment, says that Cambridge's severe winters have enhanced the city's character and served a useful purpose.

Historically, farmers relied on frozen swamps to support their carts when gathering wood, and residents once acknowledged beneficial effects of the cold, Stilgoe says.

"In the middle of the 19th century there was the belief that very cold, dry winters were good for the health," Stilgoe says. "It was once thought to be a good thing...in the same way a drafty house could be considered a good thing because it brings in fresh air."

Stilgoe even suggests that Harvard may have severe winters to thank for its academic prestige.

"There's a strong argument that all of the country's great universities are in places where the winters are bad. The damp winters like those in Cambridge keep people indoors studying."

The area's snow and cold have also enhanced local folklore. Young recounts the story of Emily Pickman, whose ghost reportedly still roams the Yard.

Pickman and her fiancee were crossing the Cambridge Common in a sleigh more than 100 years ago. When the horse suddenly panicked, the two were thrown from the sleigh. Pickman's fiancee, his neck broken, died in her arms.

The distraught Pickman buried her fiancee's body in the Old Burying Ground, only to find the crypt violated three days later and the body missing.

On the same night, Boston police apprehended an unruly drunkard dressed in gentleman's clothing. When questioned, he admitted to stealing the body, selling it to Harvard Medical School and keeping the clothes for himself.

By the time police contacted the Medical School, then located in Holden Chapel, the body had already been dismembered and used for research.

Pickman soon left Cambridge and moved to Cape Cod. But following each winter snowfall, she returned to the Yard dressed in her mourning dress and roamed in the vicinity of Holden Chapel, lamenting her loss.

For years after her death, following each snowfall, her figure was seen walking through the snow near the Chapel. The skirt of her mourning gown trailed through the snow; but there were never any footprints.

Young says she has returned after every snowfall except for the Blizzard of '78, when drifts were so deep they prevented her return.

While the lack of snow has meant fewer opportunities for Pickman to return to the Yard, scientists have more serious concerns about weather. They must determine if the recent warm winters are part of a permanent climatic change.

Climatologist Robert E. Lautzenheiser says despite a spat of warm winters and low snowfall totals, statistics show no signs of long-term warming.

Lautzenheiser began recording temperatures and precipitation in Massachusetts for the federal government in 1956. Although budget cutbacks claimed his public funding in the early 1970s, he has continued recording weather lata.

Lautzenheiser supervises a network of unofficial weather stations and makes his measurements available to the public.

Lautzenheiser acknowledges that the Boston area has experienced several unusually mild winters in recent years. But he is skeptical of theories that the regional climate has been permanently altered.

"[Recently] we have had some fairly low snow totals...but in the last 10 years or so we have had several fairly cold winters," he says. "I wouldn't say for sure that things are changing."

Lautzenheiser's records for the past 10 years show seven winters with temperatures averaging above the normal mean of 31.3 degrees and four winters averaging below. The winter of '90-'91 was the warmest in recent memory, with an average temperature of 35.4 degrees, more than four degrees above normal.

Still, improvements in snow-removal equipment and muddled childhood memories may have as much to do with the perception that winters are warmer as higher temperatures, says Lautzenheiser.

"When you're a small child, you look up at snow mounds. When you're an adult you look down on the same piles," he says. "People have been saying [the winters have been getting milder] since Jefferson. If that were really true, then we wouldn't have snow anymore."

While Lautzenheiser tries "to keep an open mind" about global warming, Rotch Professor of the Atmospheric Sciences Michael B. McElroy says that evidence of a warming trend are undeniable.

McElroy, a close advisor of Vice President Al Gore '69, cites historic reports of the sea being frozen off the coast of Maine as evidence that the climate is changing.

"Eight of the warmest winters in the past 100 years have occurred in the last 10 years," McElroy says. What can you draw from that? There's absolutely no way to be sure."

McElroy is reluctant to say definitively that the primary cause of recent warmth is the greenhouse effect. He says there are both short-term and long-term factors which influence the climate.

Short-term effects include volcanic eruptions and the El Nino phenomenon, characterized by a warming in the tropical Pacific. Long-term effects include the release of "greenhouse gases" into the atmosphere and natural climatic cycles.

"There is no absolute definitive proof that the recent warming is an effect of greenhouse gases...but we expected warming and warming has occurred," McElroy says.

"I believe in the need to be cautious. The possibility for rapid climate change is real."

Even without definitive proof that human-produced gases are warming the earth, McElroy says we must take action to reduce toxic pollutants.

He cites the discovery of the ozone hole over Antarctica in the 1970s as evidence of the folly of delaying. "If we'd known about it in the 1960s then it wouldn't have happened," McElroy says. "Now we will feel its effects until the 2300s."

McElroy may worry about milder winters, but there are plenty of people who are glad to be free of snow and cold.

To the city's growing homeless population milder winters are something of a boon.

Sam S. Ellcock Jr., assistant director of the Cambridge Corps of the Salvation Army, says the number of those seeking shelter increases by as much as 50 percent during snow and cold.

Ellcock was homeless himself until four years ago and recalls sleeping in unlocked cars and on heat grates in order to escape the cold. "A couple of times I almost froze, got frostbite. It was real brutal, real hard."

Still, some shelters worry that milder winters keep homeless people on the streets and away from shelters and other services--such as substance abuse programs.

Although four distinct seasons were once a source of regional pride, many Cantabrigians now seem somewhat ambivalent about the recent tame winters.

Young has fond memories of the beauty and silence that carried across the city after the Blizzard of '78. "It made us feel very dependent on nature's willingness to keep us here," he says.

But even Young isn't sad to see the ground bare and students walking around without coats.

"My ideal winter would be roughly 67 degrees, a gentle breeze, early budding crocuses, and two beautiful sounds: the sound of a robin and the sound of a lacrosse ball landing in the cradle."