As the first step in full-blown litigation over EPA's endangerment finding for GHG emissions, a group of agriculture, mining, and energy interests has filed a petition for review with the United States Court of Appeals for the District of Columbia. Although the petition itself does not lay out the substantive grounds on which the challenge to the endangerment finding is based, it is likely that the petitioners will take issue with the science on which the endangerment finding is based. The burden on petitioners is a heavy one; EPA's endangerment finding is not likely to be overturned unless the petitioners can demonstrate that it is arbitrary and capricious. However, if the endangerment finding is overturned, EPA would likely lack authority to require GHG emission reductions under the Clean Air Act.