According to the Intergovernmental Panel of Climate Change agriculture is responsible for a significant portion of the increase of greenhouse gases. But not all agriculture has the same impact on global warming. We conducted an extensive review of the literature on the contributions of agriculture to climate change, organized into four major areas: a) transportation of agricultural inputs, outputs, and products; b) general effects of agriculture on greenhouse gas (GHG) emissions, carbon and nitrogen cycles; c) effects on biodiversity and land use change, and d) comparative energy efficiencies.
We arrived at a conservative estimate of industrial, large-scale agriculture contributing 22% of total anthropogenic GHG emissions. Agriculture-related transportation was roughly estimated to be almost one-fifth of this amount. Food sovereignty and reinvigoration of local food systems have the potential to decrease the contribution of transportation, especially where small-scale, local practices are more efficient than practices in exporting countries. In terms of general effects of agriculture on emissions, small-scale agriculture using biodiverse, integrated systems has the potential to decrease emissions and increase carbon sequestration. We found that small-scale agriculture is also better suited to supporting mitigating effects on the nitrogen and carbon cycles, in part by maintaining biodiversity-related ecosystem services. The literature also shows that small-scale farmers in many areas are directly responsible for the minority of deforestation; where they are the dominant land-clearers, this tends to still be tied to pressure from industrial and government structures pushing them onto marginal lands. Lastly, we found that small-scale agriculture was more energy efficient, on average maintaining a higher ratio of energy output to energy input. This higher energy efficiency can thus also contribute to lower related emissions of GHGs.