Last week, shortly before Christmas, the EPA posted a quick item on its website announcing a timetable for new climate regulations on power plants and petroleum refineries. This, in turn, provoked all sorts of outrage and confusion. Industry lobbyists blasted the move. James Inhofe predicted Armageddon and pledged to do whatever it took to thwart the agency. And some commenters framed this as a fresh power grab by the Obama administration. What was harder to find, though, was an explanation of what the EPA was actually doing.

So let's roll tape. Way back in 2007, the Supreme Court ruled that the EPA was required, by law, to clamp down on carbon-dioxide and other heat-trapping gases under the Clean Air Act, assuming those gases threatened public health. And, it turns out, most scientists agree that unchecked global warming does harm the public. So it's not as if Barack Obama or EPA head Lisa Jackson have a choice on whether to regulate or not—the EPA would be breaking the law if it stood by and did nothing. (Bush officials fended off this eventuality by simply refusing to open e-mails sent by EPA staff experts.)

Over at The Atlantic, Conor Friedersdorf thinks the EPA is "disregarding [the] separation of powers." But why? How? The Clean Air Act is a law that was passed by Congress and amended several times. The law originally focused on specific toxins like lead and sulfur-dioxide, but it was intended to be updated periodically, as new science on pollution and human health came in. The Supreme Court ruled that greenhouse gases fit within this framework—and, so, the Obama administration has begun enforcing the relevant laws. Set aside whether you agree with the policy outcome. What about this is constitutionally troubling?

Anyway, on to the rules themselves. As I laid out in a primer earlier this year, the EPA is moving in two directions when it comes to greenhouse gases from stationary sources like power plants or cement factories. First, there's "New Source Review." If anyone wants a permit to build a new facility—say, a manufacturing plant or a solid-waste landfill—or enlarge an existing facility, and that project is expected to emit more than 100,000 tons of CO2 (which is a lot), they have to show the EPA that they're using the best-available pollution controls. These rules are only expected to cover a couple hundred big carbon-dioxide sources in the next few years; mostly the rules will just make it exceedingly difficult to build brand-new coal-fired plants. (That's no small matter: NASA climatologist James Hansen has argued that the world has no hope of averting severe climate change unless it stops building carbon-spewing coal plants, period.)

But what about pollution sources that have already been built? Aren't those a much bigger deal? Yes, and that's where the newly announced rules come in. Jackson is using a section of the Clean Air Act, the New Source Performance Standards, to clean up existing sources of carbon pollution. Power-plant standards will be finalized by May 2012, and oil refineries by November 2012. All told, these two rules will cover about 40 percent of greenhouse-gas emissions in the United States. The big uncertainty is over just how strict the standards will be. EPA officials are already hinting that they won't force individual facilities to reduce pollution by specific amounts or percentages—instead, the agency will merely recommend that those plants adopt cleaner technologies.

That's all assuming, of course, that Republicans in Congress don't stop Jackson first. Over at TPM, Brian Beutler details the GOP's plan for thwarting new executive-branch rules via the Congressional Review Act. The EPA will certainly be a prime target, and it's still unclear how hard Obama will fight back on this issue. As Jon Chait noted, the 2012 date for the new EPA rules does suggest that the Obama administration isn't shying away from an election-year tussle over carbon regulations. But in the past month, Jackson has also delayed new standards on ground-level ozone and toxins from boilers—quite possibly in response to Republican grumbling.

Regardless of how forcefully Jackson moves, however, it's worth noting that the EPA still can't do nearly as much as Congress when it comes to curbing carbon pollution. Last year, the House passed a cap-and-trade bill that would have cut greenhouse gas emissions 17 percent below 2005 levels by 2020. By contrast, EPA officials think they can whittle emissions down by only 5 percent in the same timeframe. That's one rationale for handing this issue over to Congress: The Clean Air Act, as written, simply isn't well-designed to handle a massive issue like climate change. Then again, there was a bill in the Senate this fall to have Congress handle carbon, and Senate Republicans (plus a few consevative Democrats) killed it with a filibuster threat. So here we are.

(Flickr photo credit: uspagegov)