A nice article in Greenwire (subscription needed) begins to lay out the legal challenges to four EPA rules that seek to regulate carbon dioxide in the absence of Congressional action.  Writes Greenwire:

The four EPA rules being challenged are December’s “endangerment finding,” which determined that greenhouse gases are a threat to human health and welfare; March’s “triggering rule,” a reconsideration of a George W. Bush-era memo that determined when greenhouse gases would be subject to regulation under the Clean Air Act; April’s “auto rule,” which set greenhouse gas emissions standards for cars and light-duty trucks; and May’s “tailoring rule,” which limited the newly triggered rules for stationary sources to the largest emitters.