Producing ethanol from sugar cane

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Cars powered by methanol (made from natural gas, by far the cheapest feedstock), compressed natural gas, and ethanol (presently made from corn) have about the same, or larger, global warming impacts as petrol- and diesel-powered vehicles. There are also environmental impacts of growing crops for this purpose: soil erosion, water runoff, nutrient depletion and so forth. Given these liabilities, the use of ethanol-from-corn should be discouraged while the use of methanol and compressed natural gas should be limited to urban fleets of buses and trucks where they could significantly reduce diesel smoke emissions.