Date: 17 June 2009
Brazil's setting aside of more than 500,000 square miles (1.25 million square kilometers) of rainforest in protected areas over the past decade may effectively buffer the Amazon from the effects of climate change, preventing Earth's largest rainforest from tipping towards arid savanna in the face of ongoing deforestation and rising temperatures, argues a new paper published in Proceedings of the National Academy of Sciences (PNAS). The conclusion is based on the application of a regional climate model, run on the assumption that all land not currently under some form of protection would be deforested across the Brazilian Amazon. Roughly 37 percent of the region is presently protected in indigenous territories and state and government reserves, while around 17 percent has already been cleared, leaving about 45 percent of the Amazon still up-for-grabs.
The study, led by Robert Walker, a professor of geography at Michigan State University, looked specifically at the impact of forest conversion on regional rainfall. It found that Brazil's protection of a core zone of rainforest would be enough to maintain precipitation across the basin and avoid the catastrophic "die-off" projected by other models, notably the Hadley model produced by the UK Meteorological Office. "The thought has been that if you deforest up to a certain point in the Amazon, the forest will completely lose the ability to recover its tropical vegetation – that you will basically convert it to a desert, especially in the south and southeastern margins of the basin," said Walker. "But our research shows that if you protect certain areas of the Amazon, as the Brazilian government is currently doing, the forest will not reach a tipping point, which means we can maintain the climate with levels of deforestation beyond which was originally thought." Walker says the results suggest the Amazon could lose up to 60 percent of its forest cover without reaching the tipping point where rainforest gives way to savanna.
"Some people think the tipping point is going to occur at 30 percent to 40 percent deforestation," Walker said. "Our results suggest this is not the case; that you can have quite a bit of deforestation – perhaps up to 60 percent – before you get to the crash point." But the study rests on the "optimistic assumption that the protected areas remain largely preserved." Some protected areas in Brazil have already been degraded by fires that escape from adjacent agricultural areas or completely deforested by developers. Still the authors are hopeful that other measures will maintain forest cover outside protected areas. These include Brazil's forest code, which requires Amazon landholders to keep 50-80 percent of their land forested, and a proposed climate change mitigation mechanism, known as internationally as REDD, that would compensate land owners for keeping their forests standing.
But while the authors seem confident that Brazil's existing protected areas will be enough to stave off large-scale drying in the Amazon, a number of other recently published papers (see "related articles" below) suggest a less rosy outlook. The PNAS paper seems to downplay the effects of climate change, which drove a severe drought in 2005 that stranded river boats, isolated communities, and contributed to massive forest fires across the Amazon. Further the rainfall measurements used in the study were based an average from 1997-2001, which effectively excludes variability seen in recent drying episodes. "This is an interesting analysis but we believe it underplays the importance of the Amazon hydrological cycle in part by not taking annual variation into account," Thomas Lovejoy and William F. Laurance, winners of the BBVA Foundation Frontiers of Knowledge Award in Ecology and Conservation Biology for their work in the Brazilian Amazon, said jointly. "Further the reality is that climate change is not included in this analysis and in the real world will be synergistic with deforestation and fire. A forthcoming World Bank study will illuminate the importance of synergies." Of course protecting the Amazon rainforest offers other benefits beyond maintenance of regional rainfall and vegetation cover. The region locks up more than 100 billion tons of carbon — more than 11 years' worth of total greenhouse gas emissions from human activities; plays an important role in global weather circulation patterns, including delivering rainfall to Central America, the United States, and southern South America; supports perhaps a third of terrestrial biodiversity; and is home to the bulk of the world's remaining indigenous people still living in traditional ways. CITATION: R.A. Walker. Protecting the Amazon with protected areas. PNAS Early Edition for the week of June 15, 2009.
Abstract: This article addresses climate-tipping points in the Amazon Basin resulting from deforestation. It applies a regional climate model to assess whether the system of protected areas in Brazil is able to avoid such tipping points, with massive conversion to semiarid vegetation, particularly along the south and southeastern margins of the basin. The regional climate model produces spatially distributed annual rainfall under a variety of external forcing conditions, assuming that all land outside protected areas is deforested. It translates these results into dry season impacts on resident ecosystems and shows that Amazonian dry ecosystems in the southern and southeastern basin do not desiccate appreciably and that extensive areas experience an increase in precipitation. Nor do the moist forests dry out to an excessive amount. Evidently, Brazilian environmental policy has created a sustainable core of protected areas in the Amazon that buffers against potential climate-tipping points and protects the drier ecosystems of the basin. Thus, all efforts should be made to manage them effectively