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Tracking
Winter's Decline

By Mark Dwortzan
Climate Change

Throughout the United States, extreme weather is becoming routine. According to the National Oceanic and Atmospheric Administration, the winter of 2010–2011 was one of the snowiest in recent years. The summer of 2011 was the second warmest on record, and the winter of 2011–2012 was the fourth warmest. Then came the icing—or lack thereof—on the cake: last March, the average temperature was 51.1 degrees Fahrenheit, a whopping 8.6 degrees above normal.

While natural weather patterns could be to blame for these developments, the recent proliferation of extreme weather is an expected outcome of global warming, which scientists have linked to the combustion of fossil fuels such as coal, oil, and natural gas. Through field and satellite observations, statistical modeling, and advanced data analysis, Boston University researchers are uncovering compelling evidence of global climate change—early warning signs that raise red flags about the future of the planet.

Increased mosquito populations and human cases of eastern equine encephalitis. A decline in frogs, salamanders, and toads. Fewer varieties of wildflowers, butterflies, and birds. As Professor of Biology Richard Primack sees it, the ecological effects of at least one consequence of global warming—shorter, milder winters—are already evident in New England, and in coming decades could become even more pronounced, potentially leading to the collapse of entire ecosystems.

A pioneer in the study of climate change in New England, Primack chose Concord, Massachusetts, as a measuring stick for winter’s decline in the region. Or perhaps Concord chose him. In 2003, a few months after he began gathering field data on key indicators of spring’s emergence in the historic town, Primack learned of a previous effort conducted by Walden author and naturalist Henry David Thoreau. In daily diary entries written in the 1850s, Thoreau kept ample notes on the arrival times of some of the exact same indicators of winter’s end: the formation of leaves, or “leaf-out”; the budding of flowers; and the appearance of migratory birds.

Comparing data found in Thoreau’s notebooks and other historical written and photographic records against modern ground and satellite observations of Concord taken between 2003 and 2011, Primack and collaborating researchers determined that, on average, leaf-out is occurring 17 days earlier and plants are flowering 10 days earlier. Migratory birds, apparently far less impacted by spring’s earlier arrival, are appearing at around the same time as when Thoreau first tracked them in the 1850s. The research team reported these findings in the February 2012 issue of BioScience.

Citing global climate change and regional urbanization (Boston’s densely built environment absorbs more of the sun’s heat than the forests it replaced) as the primary culprits, Primack believes that spring’s earlier arrival has caused a number of plant species to become locally extinct. For example, some plant species that depend heavily on water for their survival are declining as warmer temperatures cause wetlands to dry up earlier than before; the number of orchid species has declined from 21 during Thoreau’s time to 7 today.

One of the most intensive investigations of the impact of climate change ever undertaken in the U.S., collecting and analyzing multiple data sources to track winter’s decline in Concord over the past century and a half was no easy task, particularly when it came to working with Thoreau’s diaries.

“When we obtained a copy of Thoreau’s records in the fall of 2003, we knew right away that it was a gold mine, but like any gold mine, it was challenging to figure out what to do with it,” says Primack. “We had to learn to decipher his handwriting and work out the modern names for some of the plant species he identified that go by different names today.”

As Primack, his former graduate student Abe Miller-Rushing (now a scientist at Acadia National Park), and numerous BU undergraduates began walking around Concord two to three days per week in 2003, they faced an even more daunting challenge: to locate, identify, and record the flowering times of all 300 plant species that Thoreau had observed.

“After two years of attempting to replicate Thoreau’s data with limited success, Abe and I eventually determined that we didn’t need to look at all 300 plant species, because several don’t flower every year or during the spring,” says Primack. “We realized that it was the common spring wildflowers that would give us the most relevant information, so we started focusing on 43 wildflower species, such as highbush blueberries, common to both Thoreau’s time and ours.”

Perhaps the greatest challenge of all was to get the project funded.

“When I applied for National Science Foundation grants in 2003, I didn’t get funding, and several reviewers said that the proposed project wasn’t feasible and was too ambitious,” Primack recalls. “The second time I applied, reviewers remained skeptical, but the NSF said the project was innovative and funded it anyway at a reduced level. Since then, as we began collecting and analyzing additional historical data related to climate change, NSF grants have funded the project in full and without delay.”

As that funding came in, Primack was helped by a NASA satellite more than 400 miles overhead carrying a remote sensing instrument called the Moderate Resolution Imaging Spectroradiometer (MODIS) that produces cloud-free images of Earth’s surface. Guided by Crystal Schaaf, a research professor of earth and environment, the survey team was able to exploit MODIS images of vegetation in Concord over the past 10 years to significantly expand their coverage capability and home in on the timing of leaf-out across Concord.

As he continues to survey signs of spring’s arrival and document how various species are responding to warming temperatures in Thoreau’s hometown, Primack plans to increase his efforts to disseminate his findings and their implications to media and educational outlets. One thing that could make his audiences more receptive to his message is their own experiences of last winter’s early departure. As he puts it, the New England springs of 2010 (the earliest on record) and 2012 were “off-the-charts early.”

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