Watching Climate Change from the Ground and the Heavens
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. But it’s happening at BU.
For several years, Richard Primack has been prowling Henry David Thoreau’s old haunts in Concord, Mass., chronicling spring’s curtain-riser, 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.
“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 produce 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,” Schaaf says. “We use these high-quality images of the local area to establish when the vegetation in the Concord, Massachusetts, 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 collaborates 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” in the future, says Primack.
Schaaf says it’s very exciting to work with Thoreau’s records from a time before the automobile, let alone satellites, existed. The scribe of Walden kept a daily diary of his nature observations during the 1850s in Concord, noting myriad things, from temperatures to migratory bird patterns to vegetative life cycles. Primack long ago grasped that Thoreau bequeathed an invaluable baseline for measuring leaf-out times and the spring return of birds to Concord.
He and his students are also investigating how the warming trend alters trees’ and plants’ ability to absorb carbon dioxide from the atmosphere. The intuitive effect—trees would grow better as warmer temps stretch out the growing season, allowing them to vacuum more CO2 from the atmosphere—may not happen: a longer, warmer growing season could decay more material on the forest floor, which might, in turn, lead to more CO2 in the atmosphere, Primack says.
What’s beyond doubt, he says, is that children in Concord don’t see as many varieties of wildflowers, butterflies, and birds as when Thoreau took nature walks. And that’s not the grimmest fallout from the declining ecosystem. Left unchecked, a warming planet will “reach a point at which the ecosystems are going to start to fail—there won’t be enough trees, there won’t be enough birds and insects in the systems. They’re not going to be absorbing enough carbon dioxide. They’re not going to be absorbing the waters to prevent flooding. They’re not going to be creating soil.”
Last year could be a harbinger. Schaaf says that 2010 saw “the earliest spring ever on record in New England.” On that point, she notes, terrestrial and extraterrestrial viewers concurred: “Both Caroline Polgar and MODIS thought it was really early, too.”