New Effort to Quantify "Social Cost" of Pollution WASHINGTON - The Obama administration is making a second attempt to systematically account for the dollar damage from greenhouse gas pollution, even with no consensus on how to forestall global warming or whether to do so. Supporters of the idea acknowledge the tremendous difficulties of trying to translate slippery estimates into a single mathematical factor, difficulties that perhaps help explain why there is little hope of consensus now on climate policy. The new effort is an update to an estimate for the awkwardly named "Social Cost of Carbon," a range of costs, stated in dollars per ton, that carbon dioxide emissions are thought to impose on future generations. When the government totes up costs and benefits for a variety of proposed regulations, the Social Cost of Carbon is plugged into the calculation to decide how to write the regulation. The new price, used for the first time last month in establishing a standard for energy efficiency in new microwave ovens, is 50 percent to 100 percent higher per ton than the one developed in 2010. But precision is hard to come by. Some of these damages appear likely but hard to calibrate, like the extent of sea level rise. Others are less certain and thus stated as probabilities, like the increase in the number of Katrina-level hurricanes or sustained droughts, or changes that radically cut crop yields. Others are simply hard to put a dollar value on, like the extinction of species. Another difficulty is how to put a value today on a price that will be paid by future generations, which is why the cost is stated in a range. "There are multiple sources of uncertainty," said Nathaniel Keohane, a former special assistant to President Obama for energy and environment, and now a vice president at the Environmental Defense Fund. But, he said, the calculation is certainly a good idea. "Information from climate science, and better understanding of what some of the impacts are, is slowly feeding its way into the economics modeling," he said. The obscure nuts-and-bolts details of forming government policy are also unclear about just what this Social Cost of Carbon will apply to. It is supposed to be used when the government establishes new regulations, like appliance efficiency standards, or fuel economy standards. Conservatives are saying that it could be used to make big energy projects like the Keystone XL pipeline look bad. (Although the government action needed there is a permit, not a rule, and so for the time being at least, the new calculation may not be applicable. Nonetheless, the Environmental Protection Agency said in a letter to the State Department in April that the State Department, in making its decision, should consider the social cost of increased carbon dioxide emissions.) Another problem is valuing events that might not happen. "The models are extremely limited in how they capture dangerous tipping points, and catastrophic outcomes," said Laurie Johnson, an economist at the Natural Resources Defense Council. Even in appliances, the applicability of the social cost of carbon is limited. Andrew deLaski, of the Appliance Standards Awareness Project, a Boston-based nonprofit group, said that a new standard could not be approved unless it was advantageous to the buyer. In the case of microwaves, that would mean that the buyer would save more during the appliance's lifetime than the added cost of buying an efficient machine, and that other benefits like saving polar bears would not enter into the calculation. In contrast, the Department of Transportation rules on car gas mileage relied on the Social Cost of Carbon - under the old pricing system - to reach the conclusion that doubling average fuel economy would more than pay for itself. But "this is a very generalized, inexact process," said William M. Bumpers, a lawyer who usually represents manufacturers in pollution cases. He applauded the standard, however. In climate change, "there's uncertainty about the timing and magnitude of the problem, but there's no uncertainty of the problem," he said. "The only real cost of carbon that I know is wrong is zero," he said.