Yesterday, the Supreme Court of the United States dropped a tar baby into the lap of the United States Environmental Protection Agency (EPA) when the High Court ruled five to four that the EPA has both motivation and authority to regulate vehicular greenhouse gas emissions under the provisions of the Clean Air Act. What this means is that EPA is now under the gun to move forward with regulating these emissions, whether they do it voluntarily or are once again sued into it. Either way, it will be a very tricky mission indeed.

A bit of back story: In 1999, a coalition of environmental interest groups filed a rulemaking petition with the EPA, asking the agency to regulate “greenhouse gas emissions from new motor vehicles under §202 of the Clean Air Act,” which states: "the Administrator [of the EPA] shall by regulation prescribe (and from time to time revise) in accordance with the provisions of this section, standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare."

Now that climate activists have the decision they wanted, what will the EPA do?

In 2003, after years of consideration and consultation, the EPA turned down the petition for rulemaking, arguing that the Clean Air Act did not authorize it to issue mandatory regulations of greenhouse gases; and also arguing that because of ongoing political dynamics, the EPA would choose not to do so even if they had such authority. Unhappy with the EPA’s ruling, another coalition of environmental groups, this time backed by a group of state and regional governments, appealed to the U.S. Court of Appeals for the District of Columbia Circuit, to overturn the decision. The three-judge panel voted two to one in favor of the EPA, which led to a Supreme Court Appeal and yesterday’s ruling.

Others will continue to argue (with good reason) that EPA’s first inclination was the correct one. One might wonder what good it will do for the environment if the U.S. reduces greenhouse gases from vehicles, but the emissions of the developing world wipe out the impact of that effort. It is also curious that Congress is now understood to have authorized restriction of greenhouse gases in a transportation-only section of the Clean Air Act, even though they did not do so in the portions of the Act dealing with the fixed facilities that generate most emissions.

But a more interesting question may be, now that climate activists have the decision they wanted, what will the EPA do?

Unlike other pollutants, greenhouse gases aren’t emitted as an accidental byproduct of some other process, in the way that, say, carbon monoxide is emitted from the burning of gasoline. And, unlike conventional pollutants, greenhouse gases can’t easily be removed at the tailpipe, because they are chemically inert. Nor can one easily remove precursors to greenhouse gases from the fuel.

If the EPA decides to treat carbon dioxide as it does any other vehicle emission, then the agency would have to promulgate a fleet-wide CO₂ standard, stipulating a certain average emission rate per vehicle mile traveled, as it does with other vehicle emissions such as carbon monoxide, particulate matter, and hydrocarbons.

But this approach would be fraught with problems. First, unlike conventional pollutants, which can in sufficient concentrations cause real-time health harms that can be measured, the long term effects of greenhouse gas emissions are not nearly as well understood. Emissions standards for greenhouse gases are, therefore, largely arbitrary. Environmental groups will, almost certainly, sue at every turn for driving the allowable emission level to zero, as they have with ozone precursors and particulate matter standards. Second, the only real way to reduce vehicular greenhouse gas emissions is by changing the fuels we use. Simply improving efficiency won’t do it, as people drive more when they get better gas mileage, rather than less. And fuel-switching is far harder than simply bolting on a catalytic converter—it will mean remaking our transportation infrastructure to support engines that run on fuels such as natural gas, ethanol, biodiesel, or low-carbon electricity, all of which are costly, sharply limited in supply, and likely to stay that way for the foreseeable future.

Whatever EPA does, we are in for a long-running, slow-moving series of standard revisions, hearings, and lawsuits, the costs of which will all end up in the sticker price of mobility.

Kenneth P. Green is a Resident Scholar at the American Enterprise Institute.

Image Credit: Mike Gifford