The UK is aiming to cut its greenhouse gas emissions 21.5 percent below 1990 levels by 2010, a reduction almost twice as large as the one the nation committed to under the Kyoto climate change treaty. Deputy Prime Minister John Prescott announced the goal yesterday as he unveiled a draft plan for complying with the Kyoto Protocol. The UK expects to meet this ambitious goal by producing 10 percent of its electricity from renewable sources by 2010, imposing a tax on energy use, and promoting programs to improve energy efficiency in homes and autos, as well as through other efforts. Meanwhile, the European Commission yesterday proposed an emissions trading system to help the European Union meet its Kyoto commitments. The system would allow companies that are having trouble cutting their emissions to buy pollution credits from other companies that exceed their emission reduction targets.