Yesterday, the EPA formally published its finding that greenhouse gases pose a danger to public health. It's printed in the Federal Register and everything. So now that that's finished, what comes next? When do the new CO2 regulations hit? Here's a quick primer on what to expect.

First things first: In March of next year, the EPA will work with the Department of Transportation to move forward on its long-planned tailpipe standards for cars and trucks—basically just a fancy way of saying stricter fuel-economy rules are on their way (the plan is an average of 35.5 miles per gallon by 2016).

Now, what about factories and power plants and all those other carbon sources out there? That part's… still opaque, and Robin Bravender has a nice Greenwire report trying to peer through the murk. The EPA is expected to ask polluters to adopt "best-available control technology" for their carbon emissions, but what that entails, exactly, still hasn't been defined. It could mean new efficiency standards for power plants, or requirements that facilities consider switching from coal to natural gas. It probably won't mean forcing coal plants to capture and sequester their carbon, since CCS technology isn't widely available yet (nor is it cheap). Odds are the rules will be fairly general at first and gradually get more specific.

After that, there are also a couple of other options the EPA could pursue. It could, as Michael A. Livermore has argued, work with states to create a cap-and-trade system for greenhouse gases, which would, in theory, give polluters more flexibility to cut their emissions (rather than having every facility have to conform to the same rigid set of rules). Down the line, the EPA is likely to set broader performance standards for each industry—indeed, some onlookers expect that standards for cement plants could hit as early as June of next year. But that leaves plenty of questions about whether these new standards will apply to new sources or to existing sources, whether the EPA will lump CO2 together with new rules that address other pollutants like mercury, and so on...

Beyond that, there are still a lot of other sources of greenhouse gases out there. And, already, the EPA is getting swarmed with petitions from environmental groups (and states) to start regulating mobile sources besides cars and trucks—such as airplanes, marine engines, or farm equipment. Some experts think the agency could start proposing regulations for some of these sectors as early as the end of 2010.

Granted, these rules may never materialize if Congress decides to pass its own climate legislation and preempts the EPA. But we still don't know if a cap on carbon can garner 60 votes in the Senate (personally, I'd put the odds of passage at about 60-40—still far from certain). So, for now, this is the path we're on.

The other thing to note is that EPA rules could get bogged down for a few years in court challenges. The conservative Competitive Enterprise Institute has announced that it will sue the EPA, claiming that "Climategate" and those East Anglia e-mails undermine the rationale for regulating greenhouse gases. (The case seems shaky, but who knows?) And, meanwhile, the EPA has proposed a "tailoring rule" that will make sure its regulations only apply to large stationary polluters—sources emitting more than 25,000 tons per year. That way, the regulations don't hit smaller homes, churches, etc. But it's still unclear if the tailoring rule can survive a legal challenge—I've heard decent arguments both ways—and if it gets struck down, suffice to say there'll be chaos.

(Flickr photo credit: dmass)