New research by the conservation organization WWF indicates that the speed with which global warming occurs is critically important for wildlife, and that the accelerating rates of warming we can expect in the coming decades are likely to put large numbers of species at risk.
Species in the higher latitudes of the northern hemisphere, where the warming will be greatest, may have to migrate. Plants may need to move 10 times faster than they did at the end of the last ice-age. Very few plant species can move at rates faster than one kilometer per year, and yet this is what will be required in many parts of the world.
The worst affected countries are likely to be Canada and Russia, where the computer models suggest that, on average, migration rates in excess of one kilometer per year will be required in a third or more of terrestrial habitats. High migration rates will particularly threaten rare, isolated or slow-moving species but will favour weeds and pests that can move, reproduce or adapt fast. The kudzu vine and Japanese honeysuckle are examples of nuisance plants in the US that will likely benefit from global warming.
Conditions today make it far harder for species to move to new habitat than it was thousands of years ago. The last time the climate warmed anywhere near as fast as it is predicted to do this century, was 13,000 years ago when sabre-toothed tigers and wooly mammoths still roamed the earth and humans had just begun to populate the Americas.
At that time the whole of human society probably numbered in the tens of millions and all were hunter gatherers. Farming and cities did not yet exist. Now, the human population has swelled to six billion and vast swathes of habitat across the globe have been lost to urban development and agriculture. Any plant or animal that needs to move must contend with roads, cities and farms.
The WWF study shows that human barriers to climate-induced migration will have the worst impact along the northern edges of developed zones in central and northwestern Russia, Finland and central Canada.
Large-scale range shifts will have a major effect on biodiversity if species are unable to move to find suitable conditions. For example, Mexico has the highest diversity of reptiles in the world because of its ancient, isolated desert habitats. However, several species, including the threatened desert tortoise may not be able to keep pace with the warming climate. In Africa, the nyala is vulnerable to expected habitat change in Malawi's Lengwe National Park, and scientists have predicted that South Africa's red lark could lose its entire remaining habitat.
Reports of ecosystem changes due to recent global warming are already coming in from many parts of the world. Costa Rica's golden toad may be extinct because of its inability to adapt to climate changes; birds such as the great tit in Scotland and the Mexican jay in Arizona are beginning to breed earlier in the year; butterflies are shifting their ranges northwards throughout Europe; alpine plants are moving to higher altitudes in Austria; and mammals in many parts of the Arctic - including polar bears, walrus and caribou - are beginning to feel the impacts of reduced sea ice and warming tundra habitat.
A doubling of CO2 in the atmosphere has the potential to eventually destroy at least a third of the world's existing terrestrial habitats, with no certainty that they will be replaced by equally diverse or productive ecosystems, or that similar ecosystems will establish elsewhere. Unfortunately, some projections for global greenhouse gas emissions suggest that CO2 will not only double from pre-industrial levels during the 21st Century but may in fact triple if action is not taken to rein in the inefficient use of fossil fuels such as coal and oil for energy production.
Amongst the countries likely to lose 45 per cent or more of current habitat are Russia, Canada, Kyrgyzstan, Norway, Sweden, Finland, Latvia, Uruguay, Bhutan and Mongolia. Bhutan and Mongolia in particular are havens for extraordinary wildlife riches to which climate change represents an alarming new threat.
Local species loss may be as high as 20 per cent in the most vulnerable arctic and mountain ecosystems. Fragmented habitats in highly sensitive regions including northern Canada, parts of eastern Siberia, Russia's Taimyr Peninsula, northern Alaska, northern Scandinavia, the Tibetan plateau, and southeastern Australia may be most at risk.
Individual mountain species that may be under threat from global warming in isolated mountain habitats include the rare Gelada baboon of Ethiopia, the Andean spectacled bear, central America's resplendent quetzal, the mountain pygmy possum of Australia and the monarch butterfly at its Mexican wintering grounds. Many coastal and island species will be at risk from the combined threat of warming oceans, sea-level rise and range shifts, all of which can add significantly to existing human pressures.
As can be seen from these examples, and the growing body of science, an alarm is sounding. The rate of global warming may be a critical determinant in the future of the global biodiversity and we cannot afford to wait to reduce greenhouse gases. Urgent action is necessary to prevent the rate of change reaching a level that will be catastrophic for nature and which may bring about irreversible losses of our world's natural treasures.
*Adam Markham is Director of the Clean Air-Cool Planet organization based in Boston, US and *Jay Malcolm is based at the University of Toronto, Canada
(Pictures of vulnerable plants and species available from the WWF-Canon Photolibrary)