California regulators, trying to assess the true environmental cost of corn ethanol, are poised to declare that the biofuel cannot help the state reduce global warming.

As they see it, corn is no better - and might be worse - than petroleum when total greenhouse gas emissions are considered. Such a declaration, to be considered later this week by the California Air Resources Board, would be a considerable blow to the corn-ethanol industry in the United States.

If passed, the measure could serve as a model as other states and the federal government tackle carbon emissions.

That has the ethanol industry in a full-court press against the proposal, saying it risks  killing investments needed to create the next generation of cleaner, more efficient biofuels.

But California's regulators say they have no choice.

The state must asses the full climate change impact of corn ethanol under a  California law requiring a sharp cut in carbon emissions from transportation fuels. The board must encourage the use of cleaner alternatives like electricity, hydrogen and cellulosic ethanol, said board spokesman Dimitri Stanich.

The proposal would work like this: If increased production of corn-based ethanol in the U.S. raises corn prices and accelerates the conversion of rainforests and conservations lands to farmland worldwide, greenhouse emissions and loss of the carbon sink associated with such deforestation and disruption must be counted towards the biofuel's total emissions.

"Losing a carbon sink would defeat the purpose of this regulation to reduce greenhouse emissions," Stanich said.

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