THE future looks bleak for the tigers of Bangladesh’s Sundarbans mangrove forest at the mouth of the Ganges river. Today some 400 of these impressive carnivores roam through the world’s largest surviving mangrove ecosystem. By mid-century, global warming is likely to have starved the Sunderbans’ tigers into oblivion.
Colby Loucks of WWF-US in Washington DC has calculated how the Sundarbans will be affected if sea level rises at a conservative 4 millimetres per year. His maps show the forest being progressively inundated until, in 2055, the remaining fragments will average just 33 square kilometres – smaller than the hunting range of a single adult male. “These fragments would be barely able to support one tiger,” Loucks told the annual meeting of the Society for Conservation Biology in Chattanooga, Tennessee, last month.
This forecast highlights how global warming is transforming the task facing conservationists. Until now, they have tended to assume that protecting key areas of habitat will be enough to save endangered species. “Climate change really challenges this fundamental assumption,” says Sandy Andelman, who heads the Tropical Ecology Assessment and Monitoring Network at Conservation International in Arlington, Virginia. In many locations, habitats may change so radically that a nature reserve would be little more than a condemned cell for the species within.
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“Habitats may change so radically that a nature reserve would be little more than a condemned cell for the species within”
For the tigers of the Sundarbans, where rising sea level poses such an overwhelming threat, calculating the impact of climate change is relatively straightforward. But predicting the prospects for many other species and ecosystems is more complicated. Biologists must work out how they will be affected by changes in temperature, rainfall and many other climate variables.
The main problem is that most conservationists are ill-equipped to run the computer simulations required to make these forecasts. “We hardly know what to protect today,” says Heini Kujala of the University of Helsinki in Finland, part of a team working out how global warming will affect Europe’s amphibians and reptiles.
The team uses habitat models that can estimate the total range of each species from information about the climatic conditions where they live now. The researchers then simulate future climate to predict where these conditions are likely to exist in coming decades.
They have also considered how quickly each species can disperse. If the climate zones they can tolerate move faster than that, Kujala explains, species will not be able to keep up. Fortunately, most reptile and amphibian species in European centres of biodiversity should be able to migrate up nearby slopes as the lowlands warm, so protecting existing centres of biodiversity should work well until at least 2050, the team found.
But what of the countless conservationists who want to know how global warming is likely to affect their favourite species or locality, but don’t have access to expert climate modellers? Help is at hand, through a tool called the ClimateWizard, unveiled in Chattanooga by Evan Girvetz of the University of Washington in Seattle.
The ClimateWizard, devised by Girvetz and other scientists working with The Nature Conservancy (TNC), enables biologists to specify which area they are interested in, then see how its temperature and precipitation are likely to change. Users fill in a web query form and receive their answers in the form of graphs and maps.
An interface with Google Maps also allows users to see animated maps of likely changes in temperature and precipitation – a function that Girvetz believes will be particularly useful for communicating the implications of climate change to policy-makers. “When you see the changes occur, it really means a lot more,” he says.
The big limitation at present is in the level of local detail. Global climate models calculate how the climate is likely to change in individual “cells” measuring between 250 and 600 kilometres across. For a conservationist who might want to know about the future of an individual nature reserve, this resolution is much too coarse. So the ClimateWizard “downscales” its results, using knowledge of how local climate is influenced by geographical factors such as elevation, slope and nearby bodies of water.
For North America, projections into the future have so far been downscaled to a resolution of 8 km, while records of how climate has already changed are available at a resolution of 4 km. This information is now being used to reassess conservation priorities in the state of New Mexico. There, a team led by Carolyn Enquist of TNC has mapped how temperature and precipitation have changed across the state since 1991, compared with the conditions that prevailed in the preceding three decades (see map).
Enquist’s maps show that much of the state has got warmer and wetter, while other areas have warmed but become drier. Her team has also combined the results for temperature and precipitation to produce an overall measure of the threat posed by climate change at each of 231 sites listed by TNC as key conservation areas in New Mexico. Topping the at-risk list were the Jemez Mountains, west of Santa Fe, where drought has weakened the pinyon pines that dominate the local vegetation. This has made them susceptible to attack by bark beetles, causing massive die-backs. While it is too early to give up on such areas, Enquist warns that it may become necessary to refocus conservation efforts on similar habitats in locations where the climate is changing less rapidly.
Other biologists who are trying to assess the impact of global warming agree that there is an urgent need for tools like the ClimateWizard. “Making climate data available to everyone is critical,” says Shaye Wolf of the Center for Biological Diversity in San Francisco, who is forecasting how global warming will affect seabird populations. “We need a similar tool for marine systems.”
However, experts warn that climate models need to be interpreted with caution, and must be carefully related to what is actually happening in the field. David Knox, who works for the South African branch of Conservation International, says that his initial attempts to model how global warming will alter habitats in Madagascar had the entire island overrun with tidal mangroves – a topographical impossibility.
Moreover, different climate models – and different projections for greenhouse gas emissions – are likely to give divergent results. With this in mind, the ClimateWizard allows users to choose between three climate models and three scenarios for future greenhouse gas emissions.
Even if biologists avoid the pitfalls associated with uncertain predictions, there is still the question of how best to reassess their conservation priorities in the light of the forecasts. If the models merely produce a list of reserves that are doomed to destruction, it will be a profoundly depressing exercise.
Andelman believes the information will be more useful than that. For instance, studies in Madagascar have revealed upland river valleys where species clung on during previous periods of warming over the past 10,000 years. So restoring and protecting these areas, and ensuring that species from habitats threatened by climate change are able to migrate into them, should be made a priority.
“Studies in Madagascar have revealed upland river valleys where species clung on during previous episodes of warming”
Even if there is little hope of intervening to help species adapt, Andelman argues that it is still important to determine what damage is likely to unfold, as communicating this message provides another incentive to move towards greener fuels.
“There’s so much focus now on energy security,” she says. “I don’t think most people have made the connection to ecological and biodiversity security.”
