Officials in nine northeastern states have reached a preliminary agreement to control carbon dioxide emissions from more than 600 power plants. The draft regional CO2 control plan would set caps on emissions that will decrease over time. The total annual cap for all nine states--the six New England states, New York, New Jersey, and Delaware--would be 151 million tons and would be enforced starting in 2009. A trading system will enable power plants to buy and sell emission allowances. New York, the largest state, would have a cap of 65.6 million tons, and Vermont would have the smallest cap, only 1.35 million tons. Total emissions would be stabilized at 151 million tons from 2009 through 2015 and reduced 10% between 2015 and 2020. The initiative, begun in 2003 by New York Gov. George E. Pataki, will not come into force until enacted by the legislatures of the nine states. California, Washington, and Oregon are weighing a similar agreement.