Minute Shift in Temperature Has Had a Major Effect on Earth, Studies Show
Species are migrating northward because of 1-degree increase in last 100 years, data reveal. It also has sped up spring flowering, egg hatching.
The Los Angeles Times, Usha Lee McFarling, Jan. 2, 2003
Gradual warming over the last 100 years has forced a global movement of animals and plants northward, and it has sped up such perennial spring activities as flowering and egg hatching across the globe -- two signals that the Earth and its denizens are dramatically responding to a minute shift in temperature, according to two studies published today.
One study showed that animals have shifted north an average of nearly four miles per decade. Another study showed that animals are migrating, hatching eggs and bearing young an average of five days earlier than they did at the start of the 20th century, when the average global temperature was 1 degree cooler.
That 1 degree, according to the studies, has left "climatic fingerprints" -- pushing dozens of butterfly and songbird species into new territories, prompting birds and frogs to lay eggs earlier and causing tree lines to march up mountain slopes.
In some cases, the shifts have been dramatic. The common murre, an Arctic seabird, breeds 24 days earlier than it did decades ago. And some checker-spot butterflies shifted their range northward by nearly 60 miles in the last century.
Although many individual shifts in timing and range have been reported by field biologists, the studies published in today's issue of Nature are the first to establish that a variety of organisms in myriad habitats are responding in similar ways to climatic change.
"There is a consistent signal," said Terry L. Root, a biologist at Stanford University and lead author of one report. "Animals and plants are being strongly affected by the warming of the globe."
Root said she was surprised that the two Nature studies were able to detect the effect. She said she thought the increased temperature was too small to cause widespread change. Root also said she expected that any damaging effects of climatic change would be unnoticeable amid the enormous habitat destruction in modern times caused by development, pollution and other human activities.
"It was really quite a shock, given such a small temperature change," she said.
Many scientists have debated whether plants and wildlife have been widely affected by climatic change. Some have argued that no widespread response has occurred and that a few examples of animals changing the timing of their migration or reproduction have been used by environmental groups to overstate the dangers of global warming.
The new studies attempt to override such criticism by analyzing thousands of reports of biological change and correlating them with climatic change. "People said there wasn't a quantitative analysis and it was just storytelling," said University of Texas biologist Camille Parmesan, who led the other Nature study. "This is the first hard-core, quantitative analysis."
The changes are not necessarily bad for all species. The earlier hatching of eggs gives some bird species a chance to lay two clutches of eggs per summer instead of one, Root said. With less frost in late spring and early fall, the growing season of many plants has been extended; crop yields are also up.
But the scientists are concerned that warming will harm some species, particularly those already at risk. The extinction of the golden toad from the cloud forests of Costa Rica has been linked by some scientists to heat stress, Root said. And chicks of the jewel-colored quetzal bird in the same forest are now being preyed upon by toucans that moved to higher elevations in the forest as temperatures warmed, she said.
Ecosystems could also be at risk, she added, if insects mature too late to pollinate plants that now flower earlier. The earlier migration of wood warblers is leaving behind spruce trees full of spruce budworm caterpillars, which devastate the trees and leave the timber damaged.
"If we've had so much change with just one degree, think of how much we will have with 10 degrees," Root said, referring to projections by the Intergovernmental Panel on Climate Change on how high temperatures could rise in the next 100 years. "In my opinion, we're sitting at the edge of a mass extinction."
But such worst-case scenarios underestimate the ability of biological entities to adapt, some experts say. In a report written for the George C. Marshall Institute, Lenny Bernstein, an expert on the social and economic effect of climatic change, said some "marginal species" will become extinct. He added, however, that plants and animals have always faced climatic changes and that they often have survived. Future human intervention could help increase survival rates, he said.
Although the new studies do not address the cause of the recent warming, most scientists agree it is due to a mix of human and natural factors. An increasing number of scientists say that the warming is occurring at a rate unprecedented in the recent geological past and that it will be peppered by more extreme events, including heat waves, droughts, storms and floods.
"It's not just the gradual warming that impacts individuals, it's these extreme events," Parmesan said.
Convinced that wild animals and plants will need more room if warming continues, Root and Parmesan advocate including climatic change projections into long-range planning for wildlife management. Preserves may offer more options for survival if they run in a north-south direction, contain elevation gains or are connected to neighboring reserves, the scientists said.
"Since we can't count on climate being stable," Parmesan said, "you need to give the organisms a chance to go through some unstable periods."
The New York Times, Andrew Revkin Jan. 2, 2003
Global warming is forcing species around the world, from California starfish to Alpine herbs, to move into new ranges or alter habits in ways that could disrupt ecosystems, two groups of researchers say.
The two new studies, by teams at the University of Texas, Wesleyan, Stanford and elsewhere, are reported in today's issue of the journal Nature. Experts not associated with the studies say they provide the clearest portrait yet of a biological world driven into accelerating flux by warming caused at least in part by human activity.
Plants and animals have always had to adjust to shifting climates. But climate is changing faster now than in recent millenniums, and many scientists attribute the pace to rising concentrations of heat-trapping greenhouse gases.
In some cases, species' ranges have shifted 60 miles or more in recent decades, mainly toward the poles, according to the new analyses. In others, the timing of egg laying, migrations and the like has shifted weeks earlier in the year, creating the potential to separate species, in both time and place, from their needed sources of food.
One academic not associated with the studies, Dr. Richard P. Alley, an expert on past climate shifts who teaches at Pennsylvania State University, said that climate had changed more abruptly a few times since the last ice age and that nature had shifted in response. But, he noted, "the preindustrial migrations were made without having to worry about cornfields, parking lots and Interstates."
Citing the new work and studies of past climate shifts, Dr. Alley saw particular significance in the expectation that animals and plants that rely on one another were likely to migrate at different rates. Referring to affected species, he said, "You'll have to change what you eat, or rely on fewer things to eat, or travel farther to eat, all of which have costs."
The result in coming decades could be substantial ecological disruption, local losses of wildlife and extinction of some species, the two studies said.
The authors express their findings with a certainty far greater than in the last decade, when many of the same researchers contributed to reports on biological effects of warming that were published by the Intergovernmental Panel on Climate Change, the top international research group on the issue.
The authors of one of the new Nature papers, Dr. Camille Parmesan, a biologist at the University of Texas, and Dr. Gary Yohe, an economist at Wesleyan University, calculated that many ecological changes measured in recent decades had a 95 percent chance of being a result of climate warming and not some other factor.
"You're seeing the impact of climate on natural systems now," Dr. Yohe said. "It's really important to take that seriously."
Some butterflies have shifted northward in Europe by 30 to 60 miles or more, with the changes closely matching those in average warm-season temperatures, Dr. Parmesan said. The researchers were able to rule out other factors — habitat destruction, for example — as causes of the changes.
Some of these changes meshed tightly with variations in temperature over time. Dr. Parmesan cited bird studies in Britain. There, populations of the great tit adjusted their egg laying earlier or later as climate warmed early in the 20th century, then cooled in midcentury and warmed even more sharply after the 1970's.
Over all, Dr. Parmesan's study found that species' ranges were tending to shift toward the poles at some four miles a decade and that spring events, like egg laying or trees' flowering, were shifting 2.3 days earlier a decade.
Around Monterey Bay in California, warmer waters have caused many invertebrates to shift northward, driving some species out of the bay and allowing others to move in from the south.
Authors of both new papers said they were concerned that such significant ecological changes had already been detected even though global temperatures had risen only about one degree in the last century.
They noted that projections of global warming by 2100 ranged from 2.5 to 10 degrees above current levels, should concentrations of carbon dioxide and other heat-trapping gases, which flow mainly from smokestacks and tailpipes, continue to rise.
By comparison, the world took some 18,000 years to climb out of the depths of the last ice age and warm some five to nine degrees to current conditions.
"If we're already seeing such dramatic changes" among species, "it's really pretty frightening to think what we might see in the next 100 years," said Dr. Terry L. Root, an ecologist at Stanford University who was the lead author of one of the new studies.
The two teams of researchers used different statistical methods to analyze data on hundreds of species, focusing mainly on plants and animals that have been carefully studied for many decades, like trees, butterflies and birds. Both teams found, with very high certainty, a clear ecological effect of rising temperatures.
Several of the researchers said the effects of other, simultaneous human actions, like urban expansion and the introduction of invasive species, could greatly amplify the effects of climate change.
For example, the quino checkerspot butterfly, an endangered species with a small range in northern Mexico and Southern California, is being pushed out of Mexico by higher temperatures while also being pushed south by growing suburban sprawl around Los Angeles and San Diego, Dr. Parmesan said.
"The butterfly is caught between these two major human factors — urbanization in the north and warming in the south," said Dr. Parmesan, who has spent years studying shifting ranges of various checkerspot species.
Dr. Alley said the studies illustrated the importance of conducting much more research to anticipate impending harms and devise ways to maintain biological diversity, for instance with green "wildlife corridors" linking adjacent pockets of habitat.