Photo by Karen Eliot.

In my post on the new EPA carbon pollution rule, I drew attention to an important distinction: The rule issued today governs new power plants only; carbon pollution from existing power plants has not yet been regulated.

This matters a great deal. Today’s rule effectively means there will be no more coal plants built in the U.S., but that was more or less a fait accompli due to market forces. What to do about existing plants is in many ways a more fraught and important question. It could have much larger effects on near-term pollution from the power sector.

On a conference call with reporters this morning, EPA Administrator Lisa Jackson said, “We have no plans to regulate existing sources.” That caused me a few moments of panic (and, um, a few outbursts on Twitter). If there are really not going to be any existing-source regulations, that would make this whole process a massive, massive fail.

But I’ve talked to a few people and gotten a better sense of the lay of the land, and I’m here to tell you, in the words of The Hitchhiker’s Guide to the Galaxy: Don’t panic.

Here’s the story: Once something is deemed a pollutant under the Clean Air Act (which, in the case of CO2, was settled by the Mass v. EPA Supreme Court case), then it must be regulated under Section 111 of the act, the New Source Performance Standards program.

Section 111b governs new sources. That’s what was issued today. But when EPA regulates under 111b, that triggers a legal obligation for it also to regulate existing sources under 111d.

Which is a nerdy way of saying: EPA is legally obligated to regulate existing power-plant sources of CO2.

All that remains is to determine the timing. A bunch of green groups sued EPA over their delay on CO2 several years back. The settlement that was reached obligated EPA to issue CO2 regs by last September. Obviously that didn’t happen. Green groups then agreed to a few extensions. They have taken the issuance of the rule today as a sign of good faith from EPA that it’s on track.

Regulation of existing sources under 111d is a much trickier, more difficult matter than regulation of new sources. There are genuinely novel questions of law and technology involved. EPA has been grappling with these questions, but it’s not easy and there are a great many interested stakeholders, to say the least. Even if it wanted to, EPA probably couldn’t get that rule done and issued before the election.

Given that, EPA doesn’t really want to talk about it. More to the point, the Obama administration doesn’t want to force Midwestern Senate Democrats to talk about it. Here’s the thing: The rule itself is probably going to be pretty mild. It will mainly involve efficiency upgrades and demand-side measures. However, until there’s an actual rule on the table, the void will be filled by the lurid fantasies of conservatives, who warn that EPA is determined to shut down the entire U.S. coal fleet. Suffice to say, Obama doesn’t want the airwaves filled with Midwestern Senate Dems worrying over the closure of coal plants in their states.

That, I think, is why Jackson is saying EPA has “no plans” for existing sources. It’s not that they’re not going to regulate existing sources. They have to, by law. Right in today’s proposal [PDF] it makes reference to rules “EPA would promulgate at the appropriate time, for existing sources under 111(d).” When Jackson says “no plans,” what she basically means is, “no schedule.”

The existing-source rule is obviously well behind schedule, but from my conversations with green group folk, it sounds like they’re keeping their powder dry. It looks to them like EPA is working in good faith and they expect the new rule in the first year or so of Obama’s second term — assuming he has one.

If it drags out much longer than that, green groups might go back to court. But for now, they seem moderately satisfied with how things are proceeding.

It goes without saying, of course, if Republicans win the Senate and the presidency this year, all EPA regulations of CO2 will go out the window. Indeed, the EPA as we know it will cease to exist. But there’s not much Lisa Jackson can do about that.