In simple terms, accumulation of methane, carbon dioxide, nitrous oxide, and other gases that trap infrared radiation are predicted to cause global climate change, and carbon dioxide has the greatest impact because of the huge quantities released when fossil fuels are burned. Burning coal, petroleum, and natural gas, in order of decreasing impact, release previously trapped carbon into the atmosphere, resulting in a net accumulation of carbon dioxide. On the other hand, if fuels are made with renewable biomass such as wood, carbon dioxide released during processing and burning can be recaptured by photosynthesis when more biomass is grown to replace that harvested. While biomass is carbon dioxide neutral, fossil inputs to plant, grow, harvest, transport, convert, and distribute biomass and its products contribute to greenhouse gas accumulation and must be considered.
Burning bagasse can provide 100% of the thermal energy and 92% of the electricity for processing of sugar to ethanol, and less than about 8% comes from fossil sources. Based on Brazilian experience that 1.2 liters of ethanol can replace 1.0 liters of gasoline, the net contribution to carbon dioxide accumulation by vehicles running on hydrous ethanol is less than about 10% of gasoline, and substituting surplus bagasse or other renewables for fossil fuel to generate electricity could improve the balance further. However, intensive sugarcane agricultural practices raise serious concerns about its sustainability, and low and no-till and other practices will be needed for cane sugar to become more viable.