‘The 20th century ended on Friday, at least in relation to the discourse over what to do about global warming. The end came with the failure of a seven-year effort in the Senate to pass a climate bill centered on a cap-and-trade system for reducing emissions of greenhouse gases. Such a system had worked effectively for easily measured, and mitigated, emissions of conventional pollutants from power plants and other industrial sources. But carbon dioxide, the most important human-generated greenhouse gas, poses an entirely different set of challenges.’<\/p>\n