The Pew Center review of more than 40 studies is co-authored by Camille Parmesan, integrative biologist at The University of Texas at Austin, and Hector Galbraith of Galbraith Environmental Services, who is affiliated with the University of Colorado at Boulder. Their analyses revealed that more than half the studies provided strong evidence of a direct link between global warming and changes in the behavior of species in the continental United States and Alaska.
"Other recent syntheses of biological impacts, including my own, have focused on very large datasets across the globe," said Parmesan. "The conclusion from those studies is that global climate change has affected about half of all wild species. That's important, but what people really want to know is what's happening in their backyard. This is the first study to focus on U.S. datasets. The message from the report is that human-driven climate change has affected species all across the U.S., from new tropical species arriving in Florida to changes in the basic functioning of ecosystems in Alaska."
Parmesan's similar findings involving an even larger statistical review of global warming's impact on plants and animals around the world appeared in a January 2003 issue of Nature.
The Pew report, "Observed Impacts of Global Climate Change in the U.S.," involved studies of diverse plants and animals that lasted from 20 to more than 100 years. The report revealed that some plants are flowering earlier in the spring than ever before and some birds breeding earlier. In addition, species from Edith's checkerspot butterflies to the red fox have been gradually moving northward or to higher elevations, where more tolerable climate conditions now exist. Some of these species are also disappearing from southern, or lower elevation, portions of their ranges.
These shifts sometimes have had no overall negative impact. But in other cases, they have made survival tougher as the large-scale movements bring new species into contact with each other, often resulting in direct competition, such as appears to be occurring as the competitively superior red fox pushes the arctic fox farther towards the sea. But more subtle changes are also likely to result from species relocating themselves, such as changes in food quality or in availability of breeding sites.
Similar concerns exist for the Earth's waters. For example, 60 years of study have revealed that warmer-water species of fishes and intertidal species, such as starfish and sea anemone, now dominate waters near Monterey, Calif., that once were known for colder-water counterparts.
Scientists generally agree that global warming over the past century has increased average temperatures worldwide by 1 degree Fahrenheit. Although this average applies across the lower 48 states, some parts of Alaska have experienced increases of up to 7 degrees Fahrenheit. The larger the change is, the fewer species are expected to be able to biologically adjust to the new conditions.
"With warming for the next century projected to be two to 10 times greater than the last, we're heading toward a fundamental and potentially irreversible disruption of the U.S. landscape and wildlife," said Eileen Claussen, president of the non-profit Pew Center on Global Climate Change in Arlington, Va.
A 2001 report from the Intergovernmental Panel on Climate Change involving Parmesan concluded that human use of fossil fuels was primarily responsible for the average hike in temperatures over the past 50 years. Gases released from spent fuel are known to enter the Earth's atmosphere, trapping extra sunlight there similar to the way a greenhouse works. Studies since then have gone further, and also attribute a considerable chunk of recent climate change across the United States to human-released greenhouse gases.
The new report highlights actions that could be taken to reduce global warming's impact, such as providing more nature preserves that have flexible boundaries, and reducing habitat destruction and other stressors on the natural world.
Implementing a very small carbon tax to promote reduced fossil fuel use also was recently recommended in an Oct. 15 Science article by Gary Yohe, the economist at Wesleyan University in Connecticut who co-authored the 2003 Nature paper with Parmesan.
"Scientists with diverse expertise are spending an enormous amount of energy providing sound information about global warming," Parmesan said. "Without a concerted effort to minimize its impact, it's clear that species in our own backyards will become increasingly vulnerable to the effects of rising global temperatures."