As the imposition of a tax on the use of fossil fuels is debated in Pennsylvania and Virginia, along comes an analysis showing the failure of such efforts to reduce emissions of carbon dioxide in the name of saving the planet. Under a multi-state compact known as the Regional Greenhouse Gas Initiative (RGGI), Virginia already taxes producers of electricity on the basis of how much carbon dioxide they emit in burning fossil fuels — mainly coal and natural gas. Efforts to have the state withdraw from RGGI appear to have stalled. Pennsylvania officially entered RGGI July 1 and would begin...