Tapping Into a Changing Climate

Sitting in his son’s sugarhouse, Rex Marsh, 71, can recall winters so cold that no one in northern Vermont ever thought of tapping a sugar maple before town meeting day on the first Tuesday of March.

The winter snow routinely drifted 6 feet deep. Every sluggish step was in snowshoes. Even if the trees thawed, the sap would freeze in the bucket, bursting its metal seams.

“I’ve been doing this since I was big enough to carry a bucket,” Marsh said. “Tapping in January? Never. Never. Never.”

For the last two years, however, the Marshes have tapped their maples in January, the earliest they can recall in the family’s five generations of sugar making.

By mid-April -- usually their busiest time -- Marsh and his son Rick, 46, had boiled the last of their maple sap into syrup and were shutting down their oil-fired evaporator for the season.

Nestled in a grove of 9,000 maples among the sugarbush foothills of Mt. Mansfield, the Marshes’ clapboard-and-concrete sugarhouse is an unassuming outpost on the frontier of climate change.

By analyzing decades of records kept by regional maple sugar producers, climate researchers are finding clear evidence here of what Rex Marsh can feel in his bones.

The weather just isn’t what it used to be.

In Ohio and New York, through New England and into Canada, the maple sugaring season starts and ends earlier than a generation ago, University of Vermont researchers and other experts say.

Moreover, the daily temperature cycle of frost and thaw on which sap production depends also has been disrupted.

While officials argue over carbon emission controls and global warming treaties, tree farmers such as the Marsh family, along with gardeners, anglers and bird-watchers, sense the change in the air.

In response to rising global temperatures, spring comes as much as 13 days earlier in many parts of North America and 15 days earlier in Europe than 30 years ago, scientists say.

“The spring is getting earlier at a rate of a little bit more than a day per decade,” said Mark D. Schwartz, who studies the interaction between plants and climate at the University of Wisconsin in Milwaukee.

Winter is retreating as average temperatures in the U.S. have risen about 1 degree during the last century and as levels of greenhouse gases such as carbon dioxide have steadily increased to record levels, global warming studies show.

Spring and winter are becoming milder, according to the National Climatic Data Center. From 1950 to 1993, the coldest winter temperatures rose by 5 degrees, and the warmest spring temperatures rose 2.5 degrees.

On average, the temperature difference between cold nights and warm days is narrowing even more quickly.

Climate is like a pointillist composition, however, made up of myriad points of local variation -- just as the advent of spring is a collection of responses that vary by altitude and longitude, rather than a single day marked on the calendar.

Until recently, the natural variations of weather made it difficult to discern the early effects of climate change. Only now are scientists beginning to understand the interlocking gears of weather, climate, solar cycles, ocean currents and the global effects of greenhouse gases.

Searching for reliable clues, scientists turned to those who for generations have kept a precise weather eye on the seasons. Researchers have combed personal diaries, bird-watchers’ ledgers, herbarium files, museum collection notations, old photographs and naturalists’ field notes.

From these records, some encompassing centuries of observations, researchers have tracked tiny alterations in lifetime routines. The shifts reveal the imprint of climate change among hundreds of plant and wildlife species -- and among people, such as Rick and Rex Marsh, whose livelihoods are intimately tied to them.

During the last three years, a trickle of field observations has become a flood of more than 800 peer-reviewed reports documenting how plants and animals are adapting to changing temperatures.

The changes are reflected in the flight of the butterfly, the song of the tree frog, the flowering of cherry blossoms and the sap flow of sugar maples.

“The effects of climate change are becoming pretty unmistakable,” said University of Maryland ecologist David Inouye. “I suspect these changes have been going on for a while, but it has taken a long time to detect them.”

Despite the variations of local weather, there are signs of a uniform global response.

Cherry blossoms in Kyoto, Japan, where gardeners have recorded the date of first flowering for a thousand years, have altered their behavior in the same way as cherry blossoms in Michigan and Washington, D.C., German ecologists recently reported.

On either side of the Pacific, the cherry trees flower, on average, two weeks earlier than a generation ago, records show.

“People are finally starting to see the changes, spread across the world from the tropics to the Arctic and across every taxonomic group,” said ecologist Camille Parmesan of the University of Texas at Austin who reviewed the behavior of 1,700 species of plants and animals.

“You can nitpick on a single study, but now there are 800 papers looking at thousands of species,” Parmesan said.

In few regions is the weather quite so closely watched as in New England, where the rhythm of the seasons is a business cycle that encompasses maple syrup producers, ski resort operators and millions of tourists lured by the bright palette of fall foliage.

The oldest continuous weather records in North America were compiled at the Blue Hill Meteorological Observatory south of Boston. Around Concord, Mass., naturalists have been documenting the behavior of plants and animals for almost 200 years.

And there are few regions where normal weather has encompassed such extremes.

New England, with a record high temperature of 107 degrees and a record low of 50 degrees below zero, at times has been hotter than Miami and colder than Anchorage.

So much fluctuation can easily mask subtle patterns of climate change. Indeed, although Vermont and Massachusetts have warmed on average in recent years, neighboring Maine has cooled slightly.

Even so, the trend toward early spring appears to be strongest in the six New England states.

“The general pattern of warming in New England is probably greater than most of the United States,” said conservation ecologist Richard Primack of Boston University. “We can see the effects of climate change here very dramatically.”

During the last 100 years, the average temperature in Lewiston, Maine, increased 3.4 degrees. In Providence, R.I., it warmed by 3.3 degrees. In Storrs, Conn., it rose 2.4 degrees. In Amherst, Mass., and Hanover, N.H., the average temperature increased 2 degrees.

“That may not seem like much,” Primack said, “but plants and animals are responding.”

In the highlands, rivers and streams reach their spring high-water level as much as 10 days earlier than 50 years ago, scientists at the U.S. Geological Survey reported last month. Ice on dozens of lakes in Maine and adjacent states thaws sooner, other researchers reported.

By analyzing naturalist records, Primack and his colleagues have discovered that migrating wood ducks return to southeastern Massachusetts a month earlier than 32 years ago. Ruby-throated hummingbirds arrive 18 days sooner. In all, 22 species showed similar adaptations to rising temperatures.

At the same time, the plants around Harvard University’s Arnold Arboretum bloom more than a week earlier than a century ago, according to herbarium records analyzed by Primack and Abraham Miller-Rushing of Boston University.

In the sugar maple, nature crafted an especially sensitive sensor of such seasonal shifts. Its sweet-water sap is an essence of temperature change.

“Trees don’t watch the calendar,” said Rick Marsh, president of the Vermont Maple Sugar Makers Assn. “They watch the weather.”

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Every 20 seconds, a drop of maple sap slowly slipped from the spigot protruding from the maple bark and fell into a galvanized metal bucket.

It was the tree’s last sugar of the season.

To produce the sucrose-rich fluid from which maple syrup is rendered, each tree depends on a precise cycle of freezing and thawing. Cold nights and warm days are ideal. As the sap thaws and cells expand each morning, the pressure builds up inside each tree to the level of a well-inflated tire. The sap seeps through the narrow tap hole and -- eventually -- onto pancakes.

The biochemistry of maple sugar alters as the temperature shifts. It is clearest and sweetest early in the seasonal cycle, darkest and thickest in its later stages.

Around this 200-acre stand of maples on the western slope of Mt. Mansfield, winter lingered in the snowcap and in the drifts sheltered under the lee of evergreen groves. But the rising temperatures of an unusually warm spring morning were draining the energy from these natural sugar pumps.

During the previous night, the temperature had remained well above freezing; by noon, the sun had toasted the slopes. The temperature reached 56 degrees.

Prompted by the seasonal cue, the 1,780 sugar maples of the University of Vermont’s Proctor Maple Research Center diverted their energy to creating the first buds of spring.

“We are talking only a few degrees of temperature above or below a critical threshold,” said center director Timothy Perkins. “Just a small variation can make a huge difference.”

Perkins, 45, has been monitoring the rhythm of sugar maples all his life. “My father sugared, my grandfather did, his father did and his father did,” he said. “I grew up carrying sap buckets.”

About nine years ago, Perkins started hearing how sugar makers were tapping trees earlier than normal. He started collecting their records to document the pattern. Perkins tapped the center’s maples on Feb. 19 this year, earlier than in the past.

In northwestern Massachusetts, Tom McCrumm has been making maple sugar for 35 years.

For the third year in a row, he tapped his sugar orchard of 2,500 maples in February, a month earlier than 20 years ago.

Examining his own records, McCrumm, coordinator for the Massachusetts Maple Producers Assn., said the season had also been shorter.

Temperature swings are more extreme these days, with fewer of the steady fluctuations back and forth across the freezing point that the maple sugar business needs to survive.

“The average temperature may be the same, but you are not getting the regular swings,” McCrumm said. “What we call perfect sugaring weather only lasted a week this year.”

McCrumm has no idea why. He knows only what the trees have told him.

“Nothing else has changed in 300 years,” he said. “We put a hole in a tree, collect the sap and boil it down.

“The only thing that has changed is the weather.”