Land use change and the carbon debt for sugarcane ethanol production in Brazil

Farming sugarcane, as a renewable source of ethanol for use as a fuel, is a common practice in Brazilian agriculture. Despite being renewable, whether ethanol use actually reduces greenhouse gas (GHG) emissions depends on how the sugarcane is produced. Studies have shown that land use changes due to sugarcane farming are responsible for a substantial amount of the carbon emitted into the atmosphere, and may be equivalent to, or even greater than, the great “villains” of global warming–the fossil fuels. In the context of climate change, are there alternative land use changes that could create a lower overall carbon debt for ethanol and sugarcane production? In attempting to answer this question, this study aimed to: (i) map carbon stocks in the Brazilian biomes; (ii) quantify the carbon loss under different scenarios of land use changes for sugarcane-ethanol production; (iii) calculate the payback time for land conversion to sugarcane; and (iv) quantify the current areas of cultivated and degraded pasture by biome. The results show that the carbon debt from the deforestation of Brazilian biomes for ethanol production is equivalent to 608 Mg CO2 ha−1 for the Amazon, 142 Mg CO2 ha−1 for the Cerrado and 212 Mg CO2 ha−1 for the Atlantic Forest with respective payback times of 62, 15 and 22 years. However, carbon emitted from the conversion of existing pasture land to sugarcane production rather than forest would be much smaller, with a shorter payback time. We conclude that pasturelands, especially those already degraded, would be the most suitable areas for land conversion to sugarcane production for ethanol. Pasture recovery would increase carbon stocks, reduce GHG emissions and reduce the negative direct and indirect land use changes associated with sugarcane expansion in Brazil.