Read this BusinessWeek article on a recent McKinsey study.
The results are surprising. The report concludes that the U.S. can cut its greenhouse emissions in half from projected levels in 2030 at minimal cost. None of the steps would cost more than $50 per ton of carbon dioxide emissions avoided. Plus, 40% of the reductions would actually save money. That puts the overall cost at just a few dollars per ton of carbon dioxide—or in the tens of billions of dollars overall.