Are Butterflies Silent Harbingers of Global Warming?
Camille Parmesan studies the effects of global warming by chasing butterflies. Though it sounds fanciful, it is anything but. Her careful field observations of butterfly populations have provided compelling evidence of how climate change has already affected our living planet. In fact, her landmark studies have helped pave the way for a wealth of eye-opening research tracking changes in numerous other populations of plants and animals.
It all started back in the early 1990s, when Parmesan was a graduate student happily studying the diet of a species of butterfly called the Edith's checkerspot (Euphydryas editha). She was drawn into the field by her love of nature and of the butterflies themselves. "You get a feel for the pulse of the species you are working with," Parmesan says, "a kind of intuition about them." Watching her butterflies in the field, Parmesan realized that changes in their vulnerable populations could be a sensitive indicator of global warming.
Unlike the better-known monarch butterflies, which are migratory, Edith's checkerspots dwell in distinct patches no larger than the area of several football fields. As Parmesan explains, "These butterflies travel only hundreds of yards in their entire lifetime. Because these small populations are so sedentary, they will simply go extinct if their habitat is degraded by climate change."
To determine the extent to which these nonmigratory butterflies were the canaries in the coal mine of the globe's warming planet, Parmesan spent four and a half years tracing their known habitats across the species' entire range in the western part of the North American continent, from Baja to Banff. Her painstaking fieldwork entailed visiting and revisiting known habitats of the Edith's checkerspot scattered across thousands of miles of terrain. At each locale, Parmesan would crawl on hands and knees to look for evidence of the butterflies and the telltale damage they do to host plants. "Six months of the year," Parmesan recalls, "I lived out of my car in a tent."
The work paid off. Parmesan's landmark 1996 paper in the British science journal Nature was one of the first definitive worm's-eye views of the effects of climate change on a living species. When she started out, Parmesan says, she wasn't sure whether she would be able to discern the effects of climate change. But even discounting sites where urban sprawl or other human interference might have impinged upon the butterflies' habitat, Parmesan was startled to find that 80 percent of the populations of Edith's checkerspots at the southern edge of their range in Mexico and southern California had died out.
The carefully executed study clearly documented that at least one species was already being affected by global warming; in so doing it spurred a veritable flood of research to assess the effects of climate change on the planet's other plants and animals. Because of her pioneering work, Parmesan found herself at the center of a burgeoning new field of research.
In the ensuing years, Parmesan, now a biologist at the University of Texas at Austin, broadened her focus. As she explains, "I saw an opportunity to look more widely at the issue because policymakers needed to know what was happening with the natural world, but there were incredibly few biologists working on this subject to help inform them."
For instance, taking advantage of better record keeping by butterfly collectors and aficionados in Europe, Parmesan was able to join with colleagues to determine that nearly two-thirds of some 57 species of nonmigratory European butterflies were similarly dying out on the southern edge of their ranges, shifting northward and to higher elevations.
Broadening her scope even further, Parmesan teamed up with the economist Gary Yohe at Wesleyan University to analyze the new biological studies she had helped inspire. Combing the literature and subjecting data on nearly 1,700 species to a stringent set of criteria, Parmesan and Yohe found strong scientific evidence that some 52 percent of all wild species studied show signs of having been affected by climate change. Habitats have shrunk or shifted north or to higher elevations. Animal species are breeding earlier in the year, and many varieties of plants are blooming earlier than ever before.
"A huge number of species are affected," Parmesan says, adding that the evidence is "more pervasive and widespread than almost any biologists expected." Parmesan and Yohe's 2003 paper in Nature is still one of the most widely cited articles in the field of ecology and is regarded as showing some of the strongest statistical evidence yet that global warming is having an impact on a wide swath of species and regions. In the seven years since that article appeared, the research results have become stronger than ever, Parmesan says, bespeaking "an urgent need for scientists to communicate more directly to the public about the latest studies so there isn't so much of a lag in public understanding about the effects of climate change."
Parmesan's newest research effort will take her to the Alps and the tundra of Scandinavia to try to tease apart why some species of butterflies seem more sensitive to global warming than others. The research, she hopes, will help biologists "predict which species might be most sensitive over the next 100 years."
In the meantime, Parmesan's research—including her work as a lead scientist on the Intergovernmental Panel on Climate Change (IPCC)—has led her to urge conservation biologists and nonprofit groups to shift their focus from protecting particular pieces of land toward protecting and creating what she calls "habitat corridors" and gearing up to undertake "assisted colonization" efforts, repopulating some plant and animal species in more suitable climes to protect them from extinction. Only efforts of this sort, she says, can deal with the "continent-level kind of movements of species we're going to need."
"The latest research shows clearly that we face the threat of mass extinctions in coming years," Parmesan says. "My hope is that we will be able to reduce emissions enough so that assisted colonization efforts can be successful, because at the higher ranges of scientists' projections of warming trends, frankly, we're sunk."