Hundreds of Species Pressured by Global Warming

"Birds are laying eggs earlier than usual, plants are flowering earlier and mammals are breaking hibernation sooner," said Terry Root, a senior fellow with Stanford University's Institute for International Studies (IIS) and lead author of the article published in today's issue of the journal "Nature."

Root and her colleagues analyzed 143 scientific studies involving a total of 1,473 species of animals and plants for the article, "Fingerprints of global warming on wild animals and plants."

After analyzing all 143 studies, the Stanford team concluded that global warming is having a statistically significant impact on animal and plant populations around the world.

"Clearly, if such ecological changes are now being detected when the globe has warmed by an estimated average of only one degree Fahrenheit (0.6 C) over the past 100 years, then many more far reaching effects on species and ecosystems will probably occur by 2100, when temperatures could increase as much as 11 F (6 C)," Root said.

As temperatures have increased, some species began breeding and migrating earlier. Other studies confirmed that species, from butterflies and marine invertebrates, have shifted their ranges northward as temperatures rose, occupying areas previously too cold for survival.

"Our study shows that recent temperature change has apparently already had a marked influence on many species," the Stanford team wrote.

In their analysis, Root and her co-workers showed that nearly 1,200 species, some 81 percent of the total number analyzed, have undergone biological changes that were "consistent with our understanding of how temperature change influences various traits of a variety of species and populations from around the globe."

The North American tree swallow is among the bird species beginning springtime activities earlier than historically recorded. Field biologists, who kept track of some 21,000 tree swallow nests in the United States and Canada over the last 40 years, concluded that the average egg laying date for female swallows has advanced by nine days - a phenomenon that mirrors other North American studies confirming higher temperatures and the earlier arrival of spring.

Long term observations of flowering plants in Wisconsin show that wild geraniums, columbine and other species are blooming earlier than before.

Studies in Colorado found that marmots are ending their hibernations about three weeks sooner than they were in the late 1970s.

Measurements taken in Alaska revealed that growth in white spruce trees has been stunted in recent years - another expected consequence of a rapidly warming climate, Root said.

"Climate change models predict that the poles will warm more quickly than the equator, so it's not surprising that we're getting the strongest signals of biological change from Alaska and other northern regions," Root said.

A primary concern for wild species and their ecosystems is the rapid rate of change predicted during the next century.

"The problem will be the differential response of species," Root explained. "I call it the tearing apart of communities. For example, four types of warblers feed on spruce budworm caterpillars. But the birds are shifting north. What happens when the birds no longer are present in the southern portion of their ranges, and the caterpillar population is no longer kept in check?"

She predicted that rapid climate change, coupled with the loss of habitat and other ecological stressors, could lead to the disappearance of species - a consequence that might be avoided by taking proactive instead of reactive conservation measures.

"For example, there's a very high probability that global warming could contribute to a 50 percent decline in breeding waterfowl populations," Root predicted.

"One thing we might do now is to consider adjusting the bag limits for hunters so we don't add insult to injury in the coming years," Root suggests. "Because anticipation of changes improves our capacity to manage, it behooves us to increase our understanding about the responses of plants and animals to a changing climate."

The study was financially supported by the U.S. Environmental Protection Agency, the Winslow Foundation and the University of Michigan.