So it looks like either this week or next, the EPA will finally issue its long-awaited finding that greenhouse-gas emissions endanger public health. Not to keep parroting the same line, but this is a huge deal. The finding will clear the way for the agency to start regulating carbon under the Clean Air Act, although it's still unclear what rules will emerge. Odds are the EPA will grapple with vehicle emissions first—as we noted last week, the Obama administration may try to reconcile California's tailpipe-emission laws with the new federal CAFE standards to create a single, strict national fuel-economy rule.

After that, the EPA could turn its eye toward carbon regulations for stationary sources like power plants, though there's no fixed timeline for this, and no one knows what shape those rules will take. By some accounts, EPA head Lisa Jackson wants to hold back on new regulations in order to synch efforts with other climate policies (including, presumably, ongoing congressional efforts to pass an energy bill). In any case, new greenhouse-gas rules would take years to finalize, though groups like the Chamber of Commerce haven't wasted any time warning that the EPA is plotting to reduce the economy into rubble as we speak.

For a more sober take, Paul Gutermann of Akin Gump and Colin Campbell of RTP Environmental Associates wrote a smart analysis of what might happen if the EPA started regulating carbon-dioxide under the Clean Air Act. One question is whether newly built coal-fired power plants would have to employ the "best available control technology" for their CO2 pollution. Gutermann and Campbell argue that the EPA is unlikely to require coal plants to install carbon-capture-and-storage technology, since that's still pricey and could, paradoxically, lead to an increase in conventional air pollutants. Alternatively, the EPA could force coal plants to employ some combination of waste-heat capture, efficiency improvements, and co-firing with biomass. It's all still murky.

For now,  the finding will mostly put pressure on Congress to pass its own greenhouse-gas rules instead. Ed Markey, who's co-sponsored the big climate and energy bill in the House, put it bluntly on Monday: "Do you want the EPA to make the decision or would you like your congressman or senator to be in the room and drafting legislation? ... Industries across the country will just have to gauge for themselves how lucky they feel if they kill legislation." Even Republicans like Ohio's George Voinovich have been pondering much the same thing. As much as some members of Congress might prefer to kill cap-and-trade and ignore the climate issue entirely, that's not an option at this point.

(Flickr photo credit: neoyogyrt)

--Bradford Plumer