An international report has found that many biofuel policies only work by depriving people of food.

Countries such as the United States and several in Europe have set up subsidies and other bonuses to promote the use of biofuel - fuel derived from organic matter such as plants, or agricultural, commercial and domestic wastes – as a low-emission energy option.

But a new Princeton study has found that government biofuel policies rely on reductions in food consumption to generate greenhouse gas savings.

Shrinking the amount of food that people and livestock eat decreases the amount of carbon dioxide that they breathe out or excrete as waste.

The reduction in food available for consumption, rather than any inherent fuel efficiency, drives the decline in carbon dioxide emissions in government models, the researchers found.

“Without reduced food consumption, each of the models would estimate that biofuels generate more emissions than gasoline,” said Princeton researcher Timothy Searchinger.

The study looked at three models used by U.S. and European agencies, and found that all three estimate that some of the crops diverted from food to biofuels are not replaced by planting crops elsewhere.

About 20 per cent to 50 per cent of the net calories diverted to make ethanol are not replaced through the planting of additional crops, the study found.

By not replacing crops, food prices were increased, which drives consumption down.

This leads to “broad global price increases that will disproportionately affect some of the world's poor,” Searchinger said.

There has been much debate about emissions reductions from switching from gasoline to ethanol.

Automobiles running on ethanol emit less carbon dioxide, but this is offset by the fact that making ethanol requires energy derived from greenhouse gas-emitting sources, such as natural gas.

The study found that the models used by the US Environmental Protection Agency and the California Air Resources Board claim ethanol made from corn and wheat generates fewer emissions than gasoline, but these emissions actually come from reductions in food production.

That fact is buried in the methodology and not explicitly stated, the study found.

Also, while the European Commission's model found an even greater reduction in emissions, it comes with a cost of reductions in both quantity and overall food quality.

“Without these reductions in food quantity and quality, the [European] model would estimate that wheat ethanol generates 46 per cent higher emissions than gasoline and corn ethanol 68 per cent higher emissions," Searching said.

Biofuel is a young idea in Australia, but there are some small-scale, pilot and experimental projects underway.

It is possible that the study now published in the journal Science could help inform future policies and practices so that Australia can get the most out of the potential emissions reductions, without adversely affecting human health.