Ethanol - Global Warming

Corn-based ethanol provides a net energy gain of 20-30% (US Study)
Ethanol is biodegradable without harmful effects on the environment
Growing of the crops absorbs carbon and so compensates for the emissions produced
Ethanol is considered a renewable fuel.
Adding ethanol to petrol "oxygenates" the fuel, adding oxygen to the fuel mixture so that it burns more completely and reduces polluting emissions:

High-level ethanol blends reduce nitrogen oxide emissions by up to 20%
Ethanol can reduce net carbon dioxide emissions by up to 100% on a full life-cycle basis
High-level ethanol blends can reduce emissions of Volatile Organic Compounds (VOCs) by 30% or more (VOCs are major sources of ground-level ozone formation)

Corn-based ethanol production provides a net energy loss of 20-30%
Ethanol engines require 25% more fuel per mile than conventional engines.
Brazil is expanding its ethanol production by cutting down pristine rain forest to make way for an ever expanding sugar cane crop.
While ethanol may be considered greener at the point of exhaust, there is little evidence to suggest that the entire harvesting and production process is environmentally friendly and benefits global warming. More research is required in this area.
Ethanol production consumes a lot of fossil fuel and generate harmful side products.

Our research appears to conclude that ethanol is being pushed forward for political and economical reasons by the USA and many other countries in the world because it is less expensive and reduces the dependency on imported oil - rather than for the purpose of combating global warming.

While it is true that crops in the field absorb CO2 while growing, the overall savings in greenhouse gas emissions - throughout the production cycle - is difficult to quantify as a lot of fossil fuel goes into the production of the petrol substitute.