Buried in an obscure regulation on microwave ovens is a revealing change in President Barack Obama's approach to global warming.

Last week, the Department of Energy announced an update to its energy-efficiency standards for microwaves, requiring newer models to use less power while in stand-by mode.

But the bigger action was in the fine print: The agency is now using a higher figure to calculate the climate-change benefits of the rule. That is, regulators are now assuming that it's worth about $36 to avoid an extra ton of carbon-dioxide emitted into the atmosphere, up from the old figure of $22 per ton.