Washington Each spring, the robins are arriving in Wisconsin several days earlier than they did a decade ago. Endangered woodpeckers in North Carolina are laying their eggs about a week earlier than they did 20 years ago. And some of Washington, D.C.'s signature cherry trees bloom about a month earlier than they did a half-century ago.
The first signs of spring are appearing earlier in the year, and a new study from Stanford University released Monday says man-made global warming is clearly to blame.
Mother Nature has rushed spring forward by nearly 10 days worldwide, on average, in just 30 years, the study shows.
What this means, biologists say, is that the global environment is changing so fast that the slow evolutionary process of species adaptation can't keep up. Early-arriving birds could crowd out birds that migrate only in longer daylight, leaving them insufficient food. Early blossoming flowers -- such as the columbine -- could be wiped out by spring snowstorms.
"What we're really concerned about is this tearing apart of communities; some species are going to be changing, and some are not," said study co-author Terry Root, an ecologist at Stanford's Center for Environmental Science and Policy.
The peer-reviewed study, published in the Proceedings of the National Academy of Sciences, statistically links global warming from the burning of fossil fuels to signs of early spring at detailed local levels for the first time.
Stanford scientists examined 41 giant grids -- each about 150 miles wide by 150 miles long -- and looked at 130 species of birds, animals, trees and other plants that showed significant changes in springtime activity. On a global average, signs of spring appear 9.6 days earlier than they did 30 years ago.
Europe's spring moved ahead 15 days, while North America's has advanced six days, on average. But areas north of 45 degrees north latitude -- from Maine to Washington state -- saw spring species arriving more than 13 days earlier.
This has all happened while average global temperatures have risen about 1 degree Fahrenheit over the past 30 years. The consensus of mainstream climate scientists is that temperatures will rise another 4 to 10 degrees over the next century, Root said.
Duke University ecologist Norman Christensen, who didn't work on the study, said the Stanford research seems to show what biologists see when they go into the woods and swamps.
"For a lot of us who work in the field a lot, there's sort of an anecdotal sense that this (start of spring) has changed considerably," Christensen said. "In the 30 years that I've been looking at forests in the Southeast, spring tends to come a little earlier."
Root and Stanford colleague Stephen Schneider used the top global-climate computer model to look at local temperature changes as well as animal and plant changes.
Using a variety of statistical formulas, they mathematically attributed 50 percent of the species changes to man-made global warming. Another 5 percent were due to natural climate warming stemming from volcanoes and increased solar activity.
Schneider said the localized nature of the study, as well as the mathematical correlations, should help answer questions from the minority of scientific dissenters who don't see global warming as man-made or a problem.
Those dissenters say temperature figures on the ground and city heat distort measurements of global warming, while satellite data don't show significant heating.
"This jumps over the whole argument of flaws of instrumental records," Schneider said. "The plants and animals seem to think there's warming. That can't be an accident."