The new US law, which came into force late last year, increased fivefold the required amount of blending of biofuels like corn ethanol -- creating higher demand for the grain that will push up corn prices.

By 2022 some 15 billion gallons of the required 36 billion could come from corn ethanol, with the rest mandated to come from lower-carbon sources such as crop waste and switchgrass.

The new law favored corn ethanol by continuing to subsidize it while taxing sugar ethanol, Bloomberg said. This is because corn ethanol is mainly domestically produced while sugar ethanol is imported from Brazil and subject to import tariffs.

Bloomberg joined other critics of corn ethanol production in saying it was not a net producer of energy, unlike sugar ethanol. That is, corn ethanol does not yield more energy than it takes to produce, transport and use it.

Biofuels are seen by some people as a means of reducing greenhouse gas emissions and boosting energy security by providing an alternative to fossil fuels.

Richard Branson, the billionaire British entrepreneur and head of Virgin Group, agreed that sugar ethanol was preferable to corn-based biofuel. It would make more sense, he said, for the United States to grow food and let countries like Brazil use their land to produce sugar for biofuels.

"I think if America got rid of the importation duty on sugar-based ethanol, that's what would happen and I think the world would benefit from that," Branson told reporters.

Cuban leader Fidel Castro blasted the Bush administration's biofuels policy as "genocidal" in a series of articles last year, saying they threatened to worsen global hunger by pushing up prices for food crops used to make ethanol.

GLOBAL WARMING IS AS BAD AS TERRORISM

The international Sugar Cane Industry Union (Unica) has said that sugar cane-based fuel yields more energy than corn fuel, providing seven liters of ethanol per hectare compared with three liters with corn. The group also claimed that sugar ethanol production costs are lower.

The European Commission said last month that the European Union would set tougher environmental criteria for biofuels after admitting that the drive for these fuels has done unforeseen damage, like endangering rain forests in Asia and causing a rise in food prices.

Bloomberg also told reporters that global warming is just as much a threat to the human race as terrorism and the proliferation of weapons of mass destruction.

"Terrorists kill people, weapons of mass destruction have the potential to kill enormous numbers of people, global warming has the potential to kill everybody," said the head of the city where nearly 3,000 people died in the Sept. 11 attacks.

"This is really just as lethal, it's just that the results are something we will face long term," he said.

The mayor has set a goal of reducing New York's greenhouse gas emissions by 30 percent by 2030 through measures like converting the taxi cab fleet to hybrid cars by 2012 and trying to reduce city driving through "congestion pricing" or charging vehicles a user fee to the heart of the city's business district.