The EPA has recently announced a “Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases under the Clean Air Act.” It is summarized here for instance,
The Administrator signed a proposal with two distinct findings regarding greenhouse gases under section 202(a) of the Clean Air Act:
The Administrator is proposing to find that the current and projected concentrations of the mix of six key greenhouse gases—carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—in the atmosphere threaten the public health and welfare of current and future generations. This is referred to as the endangerment finding. The Administrator is further proposing to find that the combined emissions of CO2, CH4, N2O, and HFCs from new motor vehicles and motor vehicle engines contribute to the atmospheric concentrations of these key greenhouse gases and hence to the threat of climate change. This is referred to as the cause or contribute finding.
This proposed action, as well as any final action in the future, would not itself impose any requirements on industry or other entities. An endangerment finding under one provision of the Clean Air Act would not by itself automatically trigger regulation under the entire Act.
The evolution of this proposal and decision-making is pretty interesting, I think. Under Section 202(a) of the Clean Air Act, the EPA Administrator may issue standards addressing emissions of greenhouse gases from new motor vehicles or engines after the Administrator satisifes two tests. First, the Administrator must make a judgment on whether the air pollution in question may reasonably be anticipated to endanger public health or welfare, and then whether or not emissions from new motor vehicles cause or contribute to this air pollution.
Some background: In 1999, the International Center for Technology Assessment along with many other organizations filed a petition claiming that four greenhouse gases (CO2, methane, Hydroflurocarbons, and nitrous oxide) are pollutants and EPA has a mandatory duty to issue regulation under under 202(a) of the Clean Air Act, which EPA declined to do so in 2003 (a decision upheld by the Federal appeals court in Washington). The Supreme Court has reversed the decision of this lower court and holds that EPA has been charged with protecting the public’s health and welfare.
Specifically, in the case Massachusetts vs. EPA (where the Supreme Court overturned the decision of Federal Appeals Court), the argument was that congress has ordered EPA to protect Massachusetts (among other states of course) and thus the state has the right to challenge the rejection of the EPA rulemaking. The courts decision has led to the proposed findings of the EPA Administrator.
The Administrator is proposing to define the “air pollution” in 202(a) to be the mix of six greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. The first four contribute to this pollution from tailpipe emission, whereas the latter two are not emitted by vehicles. The impacts of greenhouse gases and the well documented impacts of within the United States (and supported by, but not dependent upon, impacts outside the U.S.) is what justifies this action. Technical support for such action is provided here