According to the Intergovernmental Panel on Climate Change (IPCC), agriculture is responsible for 10-12% of total global anthropogenic emissions and almost a quarter of the continuing increase of greenhouse gas (GHG) emissions. Not all forms of agriculture, however, have equivalent impacts on global warming. Industrial agriculture contributes significantly to global warming, representing a large majority of total agriculture-related GHG emissions. Alternatively, ecologically based methods for agricultural production, predominantly used on small-scale farms, are far less energy-consumptive and release fewer GHGs than industrial agricultural production. Besides generating fewer direct emissions, agro-ecological management techniques have the potential to sequester more GHGs than industrial agriculture. Here, we review the literature on the contributions of agriculture to climate change and show the extent of GHG contributions from the industrial agricultural system and the potential of agro-ecological smallholder agriculture to help reduce GHG emissions. These reductions are achieved in three broad areas when compared with the industrial agricultural system: (1) a decrease in materials used and fluxes involved in the release of GHGs based on agricultural crop management choices; (2) a decrease in fluxes involved in livestock production and pasture management; and (3) a reduction in the transportation of agricultural inputs, outputs and products through an increased emphasis on local food systems. Although there are a number of barriers and challenges towards adopting small-scale agro-ecological methods on the large scale, appropriate incentives can lead to incremental steps towards agro-ecological management that may be able to reduce and mitigate GHG emissions from the agricultural sector.

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In an article published in BioScience in 1996, ecologists Gregory S. Gilbert and Stephen P. Hubbell described the agroecological impact of Panama disease, a fungal pathogen (Fusarium oxysporum f. cubense) that infected export banana farms in the American tropics during the early twentieth century: "At least 100,000 acres of bananas were destroyed and abandoned. Facing bankruptcy, banana companies were forced to move into virgin forest for new plantings in order to escape the ravages of disease. Eventually, disease-resistant varieties came into common use and Panama disease is no longer a major commercial threat." 1 The authors' view of the damage caused by the pathogen echoed earlier assessments made by scientists and industry officials. 2 Gilbert and Hubbell's discussion of Panama disease, embedded in a broader study of plant diseases and tropical forest conservation, draws an important and often-neglected connection between the abandonment of diseased banana farms and the accelerated clearing of lowland tropical forests. Unfortunately, the ecologists stopped short of exploring the historical process-the "eventually" part-that led to the adoption of new varieties. As a result, they missed a chance to consider the significance of this process for those concerned with the conservation of biological diversity. The export banana trade in the Americas formed around a single variety: Gros Michel fruit (Musa acuminata) dominated U.S. markets between the 1890s and 1960. Gros Michel bananas were large, aesthetically pleasing, and shipped well. However, the plants proved to be highly susceptible to pathogens, including Fusarium oxysporum f. cubense. Beginning in the 1890s, the pathogen spread throughout virtually every export-banana-growing region in Latin America and the Caribbean. The dynamic created by the epidemic accelerated rates of deforestation in humid, lowland tropical regions, destabilized local economies, and indirectly heightened the incidence of malaria among plantation workers. 3 Panama disease prompted both the British colonial government and the United Fruit Com-Environmental History 388 388

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