So much of the wailing and gnashing of teeth around the climate bill in Congress revolves around the costs of curbing greenhouse-gas emissions. What about the benefits?

That is, seemingly everybody—the Environmental Protection Agency, the Congressional Budget Office, the Energy Information Administration, not to mention private-sector lobbies—has tried to tally how much it will cost to nudge America toward cleaner energy and fewer greenhouse-gas emissions. None have sought to figure out what kind of benefits the bill could...