A comprehensive summary has revealed, for the first time, the dramatic extent of disruptions now being experienced by Earth's species as a result of global warming. The extensive report compiles the results of over 100 research studies on the effects that recent climate changes have had on animals and plants throughout the world.
An international team of researchers -- including Eric Post, assistant professor of biology at Penn State, and others at institutions in Australia, France, Germany, Texas, and the United Kingdom -- published the study in the 28 March 2002 edition of the journal Nature.
"We tried to provide the biggest possible picture of what is now happening to the world's species," Post says. "I believe this is the first attempt to integrate the responses of such a large number of species and so many levels of responses to climate changes around the globe."
Post says the researchers were somewhat surprised, as the results of the study unfolded before their eyes, to see the extent of the evidence for the impact of Earth's changing climate on species worldwide. "That anyone can question whether living things are being affected by climate change now seems incredibly dubious itself," he says.
The local-to-global focus of the study ranges from how climate changes are affecting individual animals and plants, such as in the timing of migration, breeding, or plant flowering; to local populations of the same species; to communities of species and their interactions within a single habitat; to major redistributions of assemblages of species within entire ecosystems.
"All the major biomes on Earth have been affected by a temperature increase of just a little more than half a degree Celsius -- most of which has occurred during the last two decades," says Post, who describes this increase as comparable to the warming that occurs from about 8:00 to 9:30 on a typical spring morning. "That such a small change has had such an extensive effect is alarming when you consider that even conservative estimates predict the climate will heat up at least two or three degrees more."
The scientists found that, partly because global climate change is highly variable throughout the world, it is affecting different species and different locations in different ways. Some species have thrived while others in the same location have been devastated, while others do not yet seem to be greatly affected.
Robins in the Colorado Rockies, for example, who migrate to higher altitudes when climate signals tell them the spring breeding season has arrived, are finding that it is still winter at their higher-elevation breeding sites.
"The climate is warming earlier at lower elevations in the Rockies, but at higher elevations the thick winter snow has not yet melted so the robins can't get to the worms and other invertebrates that are their major food source," Post says.
"We can expect to see mass deaths in some populations, or years when very few young survive into adulthood."
The researchers also found that early-blooming species of plants now are blooming earlier in the spring, effectively lengthening their blooming period. "An analysis of 50 years of data from Norway on 13 plant species in 137 locations revealed changes directly related to climate in 71 percent of the total, with early-blooming and herbaceous species showing greater reactions to winter warming than late-blooming and woody plants," Post says.
The study also points out that climate change has an immediate effect on certain species but a delayed, and possibly stronger, effect on others. "We are seeing a direct and immediate correlation with warming temperatures in the first springtime sightings of butterflies, for example, which have a short lifespan and whose transition from larvae to adult is closely related to temperature," Post says.
"Large mammals, in contrast, carry throughout their longer lifetimes the effect of climate conditions that prevailed since they were born, affecting their lives in more complicated ways."
The study suggests that some species now could become invasive pests when introduced to new locations -- inadvertently or intentionally -- by humans. Whereas a century ago a species might not have been able to survive in a given location, that same species might thrive there today if climate changes have made the location more suitable for that species.
"Although ecologists have a really good grasp on how abiotic factors like temperature and rainfall influence life processes for individuals and entire populations -- like the timing of reproduction and its effect on the survival of offspring -- it is difficult to predict the effect of climate change on certain species in specific areas because nobody can predict exactly how the climate will change there."
The study reveals that sudden climate events that have an extreme local effect can have significant consequences for groups of local species. "We are seeing evidence in the Sonoran Desert in the Southwestern United States, for example, that just one extreme El Nino event can send a ripple through the biological community, tipping the ecological balance a little bit in favor of one species over another, which can result in a whole new assemblage of species," Post says.
When there is a major redistribution of groups of species as a result of environmental change, some species do well and some don't. "If the frequency of extreme climate events is increasing, as some suspect it is, that adds another very unpredictable factor when we try to foresee the ecological future at a specific location."
Another species the researchers describe is the North Sea cod, which is the foundation of a number of economies, an important food source, and a species whose future many people would like to be able to predict.
"Climate-related stresses are exacerbated for this species by the additional stress of intense commercial fishing. Each stress independently decreases the probability that a juvenile cod will live to adulthood," Post says.
"When people put very intense stresses on an animal population that also is experiencing environmental stresses, it is very difficult to tell how the two will interact and the result is an almost impossible guessing game of predicting whether the population will be pushed over a threshold beyond which it cannot survive if environmental conditions suddenly change."
The scientists find it difficult to impossible to make predictions about the how specific species at specific locations will fare at any point in the future. "If climate temperatures increase suddenly instead of gradually, of if we have one exceptionally unusual warm season, or if there is an unforeseen sudden climate change, then past climate history would become irrelevant as a tool for predicting what will happen in the future," Post says. In addition, some ecological changes could be gradual until they reach an unknown critical point, at which a sudden catastrophic event could occur.
"The recent disintegration of an ice shelf in Antarctica surprised everyone because it broke apart so suddenly instead of melting gradually. If those kind of break points exist elsewhere in ecology, we are on very thin ice in trying to predict the future of living things on the basis of the past history of the climate system," Post says.
"The complexity revealed by this research can be perplexing for government policymakers and others who want reliable predictions to guide their decisions," Post says. "Nevertheless, this complex picture reveals that we need to study each location and each species and each set of local population dynamics individually as we try to understand the effects of climate change."
For many years, a guiding principle of environmentalists has been to "think globally, then act locally." Now, in the context of the Earth's unpredictably changing climate, Post says "We have to think globally and study locally before we will know how best to act locally -- we can't take any species or any part of the Earth for granted."
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Pennsylvania State University
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