While reducing greenhouse gases will have costs, so will the results of climate change. That may seem obvious, but up until now the debate over climate legislation has only focused on the costs, without looking at the benefits.

Last week, a federal interagency taskforce released preliminary findings that began to set a dollar value for the negative effects of climate change. Often referred to as “the social cost of carbon,” this estimate is key to exposing the hidden costs of a high-carbon economy. If we only focus on the costs of cutting greenhouse gas emissions, we are seeing only half the story—inaction on global warming will lead to a greater economic hit than the price tag on the Waxman-Markey bill.

The interagency taskforce put the social cost of carbon at between $5 and $55 per ton–a conservative estimate. It was publicized in the Department of Energy’s regulation on the energy efficiency of vending machines–the first regulation after the taskforce’s results were in. While the numbers need to be revised, the process is a vast improvement from the ad hoc way that the greenhouse gas emissions have been account for in the past, including simply ignoring them (PDF).

For years we have been looking at only one side of the coin–the negative effects of regulating carbon emissions. Now that this interagency process has started to place a number on the price of emissions, we can use it to finally compare apples to apples — and the results are overwhelmingly in favor of taking action.

Nowhere is this more apparent than in the debate over the Waxman-Markey cap-and-trade legislation in the Senate. There has been a great deal of hand-wringing over the cost of this bill. But until now there has been little discussion of the benefits side of the equation. In a recent report (PDF), the Institute for Policy Integrity used the new social cost of carbon estimates to compare both sides of the ledger. With these numbers we were able to calculate that the benefit to cost ratio of Waxman-Markey would be as much as nine to one or more.

While having any SCC is better than none, the range that this interagency process has estimated is decidedly conservative, and if it is used to set policy, it will result in watered down regulations. The first step was getting the federal government to start putting economics to use to defend greenhouse gas reductions — the next step will be making sure they get the numbers right.