BRUSSELS, Belgium -- Another study is questioning the net environmental benefits of biodiesel -- this time in Europe, where biodiesel and ethanol are heavily subsidized.

Reuters recently obtained a European Union document through a freedom of information (FOI) request which shows that greenhouse gas emissions generated by the production of biodiesel can be up to four times greater than diesel or gasoline.

The study was not made public until Reuters invoked its FOI rights.

According Reuters, the EU has found that clearing and burning forest land results in carbon dioxide emissions that cancel out the benefits of biofuels.

The document states that soybean-based biodiesel, the most popular form of the alternative fuel, can indirectly produce 339.9 kilograms of carbon dioxide emissions per gigajoule -- which is said to be four times the amount of emissions of standard diesel.

Other studies in recent years have made similar "carbon debt" claims. Critics suggest that most literature showing the GHG-reduction benefits of ethanol and biodiesel do not take into account certain land use changes as biofuels become high-demand commodities. Nor are many of the costs of converting good cropland into fuel production properly considered.

In response, the National Biodiesel Board -- an association of biodiesel producers in the U.S. -- claims the EU study's estimates were biased to European products, and did not follow proper lifecycle analysis for U.S. products.

-- with files from Truckinginfo.com