Yesterday, the other big climate news that broke, apart from the release of the Kerry Boxer-bill in the Senate (and, do take note, the official moniker appears to be "Kerry-Boxer," not "Boxer-Kerry"), was that the EPA clarified new rules for regulating greenhouse gases from large stationary sources—from coal-fired power plants to refiners to large factories. I'm just going to rip off Dave Roberts's lucid summary:

When the new EPA fuel economy regulations [for vehicles] go into effect in 2010, that will automatically—as in, by law—trigger regulations of stationary sources. Such sources will have to get permits showing that they’ve used Best Available Control Technology to reduce CO2. BACT has not yet been defined for CO2. That’s going to be a huge and incredibly contentious fight.

Right. What's the best way to control CO2 from coal plants? Sequestering the carbon? Co-firing with biomass? Efficiency improvements? No one's sure yet! Anyway, that leads us to yesterday's proposed rule:

What was announced today is the “tailoring” rule; it establishes that when the EPA regulates stationary sources, it will only regulate those that emit more than 25,000 tons. This is a modification of the threshold now in the Clean Air Act, which is 250 tons. If EPA regulated every source emitting more than 250 tons, it would be a nightmare (churches! schools! marathons!). There’s some dispute about whether the EPA is legally allowed to do this; not surprisingly, I hear different things from different sides of the aisle. It is sure to be litigated.

From a political standpoint, I'd be curious to know if yesterday's EPA announcement was intentionally timed to coincide with the release of the Kerry-Boxer bill. Because, in essence, the EPA is warning the Senate that if it doesn't pass its own climate legislation, the agency will start regulating greenhouse gases next year regardless. (Last week, Lisa Murkowski tried and failed to pass a Senate amendment that would've nullified the EPA's authority over CO2.) The pressure's on.

Related: Michael Livermore argues that EPA regulation is a viable, if flawed, fallback option.