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Winter-Spring 2012 Table of Contents

Watching Climate Change from the Ground and the Heavens

Scientists get an assist from Thoreau

| From Explorations | By Rich Barlow. Video by Nicolae Ciorogan
Watch this video on YouTube

In the video above, Richard Primack measures climate change with the help of Henry David Thoreau’s notes and satellite maps. Photos by Vernon Doucette

It sounds like science fiction: a research project spanning centuries (the 19th to the 21st, to be exact), the living and the dead, and lab sites from Walden Pond to outer space.

For several years, Richard Primack has been prowling Henry David Thoreau’s old haunts in Concord, Mass., chronicling spring’s curtain-raiser, the arrival of leaves and buds. Thoreau carefully recorded the same details a century and a half ago. Primack, a College of Arts & Sciences biology professor, who pioneered the study of the effects of climate change on New England, has used Thoreau’s records to confirm that leaf-out arrives earlier today than it did then—a barometer of global warming. (He also checked photographs of leaf-out going back to the 1800s; those photos’ dates also indicate that spring came later in horse-and-buggy days.)

To corroborate his work, Primack has some eyes looking over his shoulder—from 438 miles up. He’s comparing his observations on the ground with images of vegetation generated by orbiting satellite sensors from NASA. BU colleague Crystal Schaaf is the principal investigator using the image-making technology. Both she and Primack “can identify the greening-up period, within a couple of days,” says Schaaf, a CAS research professor of geography and environment. “And we can see that these green emergence dates are occurring quite a bit earlier than in Thoreau’s time.”

On average, 17 days earlier, says Caroline Polgar (GRS’13), a postgraduate student working with Primack. He says that “it’s absolutely certain” that climate change, plus the urban furnace effect (Boston’s pavement and buildings absorbing heat, and the many cars in the area generating it) are the causes. Primack puts one-third of the blame on global warming and two-thirds on urbanization.

“Certain species of plants are not able to respond to this changing climate and are going extinct,” he says. “They’re declining in Concord, because they’re not able to respond to these warming temperatures.” Warmer temperatures dry up wetlands, for example, rendering them uninhabitable for more water-dependent plants. Exhibit A: orchids.

Richard Primack has used Henry David Thoreau’s records to confirm that leaf-out arrives earlier today than it did 150 years ago—a barometer of global warming. He’s comparing his observations with images of vegetation generated by orbiting NASA satellite sensors.

“In Thoreau’s time, there were 21 species of orchids in Concord, and now we can only find 7,” Primack says. “We’re investigating how this decline has occurred, and also what to do about it.”

In the last year, those investigations have teamed him with Polgar, as well as with Schaaf. NASA launched the Earth-observing satellite Terra in 1999 and the Aqua satellite three years later, both packing MODIS (moderate-resolution imaging spectroradiometer) technology. MODIS produces images of the entire planet at three levels of detail, every day. “On each orbit, Terra passes the equator at about 10:30 in the morning, while Aqua crosses the equator at about 1:30 in the afternoon,” says Schaaf, who attended the satellite launches at California’s Vandenberg Air Force Base.

This so-called remote sensing yields “cloud-free, atmospherically corrected nadir images of the Earth’s land surfaces,” she says. “We use these high-quality images of the local area to establish when the vegetation in the Concord, Mass., area begins to grow and starts photosynthesizing in the spring.” She and Primack had joined on previous research, and “it seemed to make sense to collaborate with Richard and see how our satellite-derived measurements of vegetation growth compared to the field measurements that his team has been collecting.”

By sharing observations on land and from space, the researchers hope to gain a clearer understanding of climate change and its effects. Primack says his on-the-ground observations are the most accurate gauge, but cover a limited geographical area; satellites cover far more terrestrial real estate, but given how far away they are, require on-the-ground confirmation. Results from both, in turn, can be added to the findings of the Boston Area Climate Experiment (BACE), an outdoor laboratory in Waltham, Mass., run by Purdue University and the University of Massachusetts, Boston. Primack’s BU lab is one of several around the country that collaborate with BACE, which compares leaf-out times of plants under regular conditions with those under artificially heated conditions.

Comparing results from these different approaches will create “much more accurate models of how climate change will be affecting forest growth in this region,” says Primack.

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