http://www.nytimes.com/2008/02/08/sc...hp&oref=slogin

Almost all biofuels used today cause more greenhouse gas emissions than
conventional fuels if the full emissions costs of producing these "green"
fuels are taken into account, two studies being published Thursday have
concluded.

The benefits of biofuels have come under increasing attack in recent months,
as scientists took a closer look at the global environmental cost of their
production. These latest studies, published in the prestigious journal
Science, are likely to add to the controversy.

These studies for the first time take a detailed, comprehensive look at the
emissions effects of the huge amount of natural land that is being converted
to cropland globally to support biofuels development.

The destruction of natural ecosystems - whether rain forest in the tropics
or grasslands in South America - not only releases greenhouse gases into the
atmosphere when they are burned and plowed, but also deprives the planet of
natural sponges to absorb carbon emissions. Cropland also absorbs far less
carbon than the rain forests or even scrubland that it replaces.