There's growing consensus that the United States needs to reduce heat-trapping pollution by up to 80 percent over the next 50 years. Democratic leaders in Congress have even committed to a cap-and-trade program that promises to find emission cuts across the U.S. economy with the lowest costs to consumers and industry. But key players are split on a critical question behind cap-and-trade: how to distribute credits worth tens or even hundreds of billions of dollars to the carbon dioxide-belching industries faced with a mandatory new U.S. carbon market.