Tropical deforestation is estimated to cause about one-quarter of anthropogenic carbon emissions, loss of biodiversity, and other environmental services. United Nations Framework Convention for Climate Change talks are now considering mechanisms for avoiding deforestation (AD), but the economic potential of AD has yet to be addressed. We use three economic models of global land use and management to analyze the potential contribution of AD activities to reduced greenhouse gas emissions. AD activities are found to be a competitive, low-cost abatement option. A program providing a 10% reduction in deforestation from 2005 to 2030 could provide 0.3-0.6 Gt (1 Gt ‫؍‬ 1 ؋ 10 5 g) CO2⅐yr ؊1 in emission reductions and would require $0.4 billion to $1.7 billion⅐yr ؊1 for 30 years. A 50% reduction in deforestation from 2005 to 2030 could provide 1.5-2.7 Gt CO 2⅐yr ؊1 in emission reductions and would require $17.2 billion to $28.0 billion⅐yr ؊1 . Finally, some caveats to the analysis that could increase costs of AD programs are described.carbon sequestration ͉ climate change ͉ reducing emissions from deforestation and ecosystem degradation (REDD) ͉ marginal cost ͉ tropical forest T ropical deforestation is considered the second largest source of greenhouse gas emissions (1) and is expected to remain a major emission source for the foreseeable future (2). Despite policy attention on reducing deforestation, Ϸ13 million ha⅐yr Ϫ1 of forests continue to be lost (3). Deforestation could have the effect of cooling the atmosphere (4), but it also leads to reductions in biodiversity, disturbed water regulation, and the destruction of livelihoods for many of the world's poorest (5). Slowing down, or even reversing, deforestation is complicated by multiple causal factors, including conversion for agricultural uses, infrastructure extension, wood extraction (6-9), agricultural product prices (10), and a complex set of additional institutional and place-specific factors (11).Avoided deforestation (AD) was included alongside afforestation as a potential mechanism to reduce net global carbon emissions in the Kyoto Protocol (KP), but until recently, climatepolicy discussions have focused on afforestation and forest management. Discussions about new financial mechanisms that include AD provide optimism for more effective synergies between forest conservation and carbon policies (11)(12)(13)(14). In 2005, Papua New Guinea and Costa Rica proposed to the United Nations Framework Convention on Climate Change that carbon credits be provided to protect existing native forests (15). The proposal triggered a flurry of discussion on the topic. SoaresFilho et al. (16), for example, suggest that protecting Ϸ130 million ha of land from deforestation in the Amazon could reduce global carbon emissions by 62 Gt (1 Gt ϭ 1 ϫ 10 15 g) CO 2 over the next 50 years.Although the potential for AD activities to help mitigate climate change is widely acknowledged (16,17), there is little information available on what the costs might be globally. This article uses t...

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