Role of global warming in extinction may be overestimated
Role of global warming in extinction may be overestimated
March 1, 2007
Extinction is a hotly debated, but poorly understood topic in science. The same goes for climate change. When you bring the two together to forecast the impact of global change on biodiversity, chaos reigns. While many ecologists argue that climate change could well doom many more species to extinction, others say that the threat is overstated.
A new paper published in Bioscience sides with the latter contention, noting that “surprisingly few species became extinct during the past 2.5 million years” despite a series of ice ages. However, the paper also argues for the critical need to develop better methods to forecast extinction rates under various global warming scenarios. Without these it will be difficult to set effective priorities for conservation efforts.
The paper, authored by an international team of 19 researchers, sets forth eight recommendations for improving global warming-induced extinction forecasts.
- Select a specific definition of biodiversity. Is biodiversity defined at the gene, population, species, or ecosystem levels? How is biodiversity best valued?
- Evaluate models before using them. “Models that forecast the impacts of climate change on biodiversity are difficult to validate, and it may be many years before anyone can conclude whether a given forecast of the effects of global warming on biodiversity was nearly right or not,” the authors write. “Scientists can and should evaluate a prospective forecasting method before using it to generate forecasts.”
Wright and Muller-Landau projections: A study published last year showed that global biodiversity concerns extend beyond climate change. Deforestation alone could doom 10-20 percent of tropical species to extinction. Some scientists dismissed these forecasts as “too optimistic.” Africa
Forest cover in Africa (2000): 31-35%
Projected cover in Africa (2030): 18-28%
Projected extinction in Africa (2030): 16-35%
Forest cover in Indo-Malaya (2000): 39%
Projected cover in Indo-Malaya (2030): 33-39%
Projected extinction in Indo-Malaya (2030): 21-24%
Account for multiple causes of changes in biodiversity. Climate change is only one of many factors affecting biodiversity, note the authors. Forecasts must include other impacts like land use, hunting, introduction of alien species, and pollution as well as natural environmental risks.
- Obtain good information and make better use of it. Data on biodiversity is currently insufficient for most needs. More work is needed to provide critical species and ecosystem data to scientists and policymakers.
- Use the Quaternary fossil record to understand mechanisms that preserve biodiversity, and use these in forecasting models. The fossil record does a poor job supporting the contention that large-scale species extinction occurred over the past 2.5 million years. The authors note a “Quaternary conundrum: While current empirical and theoretical ecological results suggest that many species could be at risk from global warming, during the recent ice ages surprisingly few species became extinct.” Is this the result of species adaptation and migration or gaps in the fossil record? Present data can’t tell us one way or the other. The authors also warn that “species might in fact be more vulnerable than the fossil record indicates.”
- Improve widely used modeling methods. The authors note that four models currently used for estimating the “quantitative forecasts of effects of global warming on biodiversity” can be improved, especially in terms of the scale to which models should be applied. “The question boils down to whether it is better to know a lot of detail about fewer points or much less information about much greater areas,” they write.
- Improve ecological principles embedded in general atmosphere—ocean—biotic coupled circulation models. Current oceanic-atmospheric models do not integrate biodiversity into climate projections despite its impact on climate dynamics.
- Develop better models for forecasting total biodiversity. Most biodiversity projections are based on the species-area curve, which holds that there exists a tight correlation between the area of habitat and the number of species. However this relationship faces limitations when dealing with climate change. Given this, new models, based on deeper analysis of why there is an observed correlation between species and area, need to be developed to forecast the impact of climate change on global biodiversity.
Spoonbill in Uganda
The authors say that their eight recommendations can improve the four types of models currently used to forecast the impact of global warming on biodiversity. They emphasize the importance of communication between branches of science — “scientists using each of those approaches tend not to communicate with each other or read each other’s literature,” they note — and propose “an integrated framework for forecasting the impacts of global change on biodiversity.”
“Such a framework could integrate models for species persistence and consider multiple causes of biodiversity change,” they conclude.
Authors of the paper include Daniel B. Botkin, Henrik Saxe, Miguel B. Araújo, Richard Betts, Richard H. W. Bradshaw, Tomas Cedhagen, Peter Chesson, Terry P. Dawson, Julie R. Etterson, Daniel P. Faith, Simon
Ferrier, Antoine Guisan, Anja Skjoldborg Hansen, David W. Hilbert, Craig Loehle, Chris Margules, Mark New, Matthew J. Sobel, And David R. B. Stockwell.
CITATION: Daniel B. Botkin et. al (2007). Forecasting the Effects of Global Warming on Biodiversity. BioScience March 2007 / Vol. 57 No. 3 227-236
In recent years, scientists have warned of a looming biodiversity extinction crisis, one that will rival or exceed the five historic mass extinctions that occurred millions of years ago. Unlike these past extinctions, which were variously the result of catastrophic climate change, extraterrestrial collisions, atmospheric poisoning, and hyperactive volcanism, the current extinction event is one of our own making, fueled mainly by habitat destruction and, to a lesser extent, over-exploitation of certain species. While few scientists doubt species extinction is occurring, the degree to which it will occur in the future has long been subject of debate in conservation literature. Looking solely at species loss resulting from tropical deforestation, some researchers have forecast extinction rates as high as 75 percent. Now a new paper, published in Biotropica, argues that the most dire of these projections may be overstated. Using models that show lower rates of forest loss based on slowing population growth and other factors, Joseph Wright from the Smithsonian Tropical Research Institute in Panama and Helene Muller-Landau from the University of Minnesota say that species loss may be more moderate than the commonly cited figures. While some scientists have criticized their work as “overly optimistic,” prominent biologists say that their research has ignited an important discussion and raises fundamental questions about future conservation priorities and research efforts. This could ultimately result in more effective strategies for conserving biological diversity, they say.
Humans, not climate change, caused the extinction of megafauna in Australia contends a team of Australian researchers writing in the January issue of the journal Science. Australia lost 90 percent of its largest animals, including a saber-toothed kangaroo, a marsupial lion and giant goannas, within 20,000 years of man’s arrival some 50,000 years ago. Scientists have long debated whether the demise of Australian megafauna was due to human arrival, climate change, or a combination of the two factors. The new research found that the climate in southeastern Australia was little different 500,000 years ago, suggesting that climate change was not the ultimate cause of extinction.
Most mass extinctions were caused by gradual climate change rather than catastrophic asteroid impacts says Peter Ward, a paleontologist at the University of Washington in Seattle, in an upcoming article in New Scientist magazine.