Go into business selling licenses for energy use in excess of legally defined limited amounts. The WSJ explains how it’s done:

The idea of a cap-and-trade system for limiting carbon-dioxide emissions in the U.S. has become all the rage. Earlier this year, 10 big American companies formed the Climate Action Partnership to lobby for government action on climate change. And this week the private-equity consortium that is bidding to take over Texas utility TXU announced that, as part of the buyout, it would join the forces lobbying for a cap on carbon emissions.

But this is not, as Lenin once said, a case of capitalists selling the rope to hang themselves with. In most cases, it is good old-fashioned rent-seeking with a climate-change patina.

Start with the name. Most of those pushing this idea want you to think about it as cap-and-trade, with emphasis on the trading part. Senator Barbara Boxer touts all the jobs that would be created for people trying to game the system — er, save the planet. And her colleague Jeff Bingaman calls cap-and-trade “market based,” because, you know, people would trade stuff.

But for that to happen, the government would first have to put a cap on CO2 emissions, either for certain industries or even the economy as a whole. At the same time, it would allocate quotas for CO2 emissions, either based on current emissions, or on energy output, or some other standard. If a company then “over-complied,” which means it produced less carbon dioxide than it was allowed to under the rules, it could sell the excess allowance to someone else. That someone else would buy the right to produce CO2 if doing so cost less than actually reducing emissions.

In this way, emissions would be reduced in an relatively efficient way: Those for whom reductions were cheap or easy would reduce, and if they reduced enough, they could sell their excess allowance to someone for whom the reductions were harder or more expensive. This kind of trading works, and we’ve argued in these columns that cap-and-trade beats the pants off just plain capping by lowering the overall economic burden of a cap.

The difficulties don’t lie with the trading, but with the cap, which is where the companies lobbying for restrictions come in. James Rogers, CEO of Duke Energy, put it plainly earlier this year: “If you’re not at the table when these negotiations are going on, you’re going to be on the menu.” Translation: If a cap is coming, better to design it in a way that you profit from it, instead of being killed by it.

Make no mistake, this “vital environmental policy measure” is on the way. Al Gore is already in the business, and will probably make billions.

Saving the earth has got a lot in common with the sarcastic old song about the profit potential in the old days in the other kind of salvation:

My father’s a missionary preacher.
He saves fallen women from sin.
He’ll save you a blonde for a guinea.
My God, how the money rolls in!