The U.S. could significantly cut its emissions of carbon dioxide (CO2), the chief heat-trapping greenhouse gas, by making a few fairly simple and inexpensive changes to its energy policies, according to a study released yesterday by the U.S. Department of Energy. The study suggests that the U.S. could get three-quarters of the way to meeting its emissions-reduction targets under the Kyoto climate change treaty by taking steps such as establishing strict energy- and fuel-efficiency standards and launching a domestic emissions-trading system that would give companies a financial incentive to cut their CO2 emissions. The report will be presented today to negotiators from more than 160 countries gathered in The Hague, Netherlands, to hammer out the details for implementing the Kyoto Protocol. Some American politicians and business interests argue that the U.S. should not ratify the treaty because it would hurt the nation’s economy, but the new DOE study suggests that cutting emissions would not have to be costly.