Two U.S. senators, Democrat John Kerry and Independent Joe Lieberman, are set to unveil their long-awaited plan to limit greenhouse gas emissions today, but Washington is skeptical the bill has much chance of passing anytime soon. Their general idea is to promote clean energy by forcing reductions in carbon dioxide emissions from burning fossil fuels by creating what’s called a cap-and-trade system, first for power plants and, later, factories. Companies would obtain emission permits at a set price. The U.S. government would send two-thirds of the revenue from emissions permit sales back to consumers as refunds on their utility bills, in a bid to offset energy cost increases. Many details remain to be explained today.