As reported in today's New York Times, responding to the Supreme Court's decision in Massachusetts v. EPA, the Environmental Protection Agency (EPA) plans to declare CO2 and other greenhouse gases as an air pollutant under the Clean Air Act which would likely lead to the establishment federal GHG emission standards for motor vehicles. At the same time, EPA is widely expected to grant California's waiver request for its CO2 vehicle pollution program sometime in the next few months. Thirteen other states and the District of Columbia have adopted those standards and more states are considering doing the same.

A number of key decision makers, including the Chair of the California Air Resources Board and representatives of the Obama Administration, have begun talking about a "single national standard" to help solve the so-called patchwork problem which is widely understood to be referring to an EPA GHG standard (not a fuel economy standard through a CAFE program) that would be equivalent to applying the California program nationwide.  In addition, though GHG and CAFE standards are clearly distinguishable, it is useful for comparison purposes to understand what impact potential EPA GHG emission standard would have on combined fleet average fuel economy levels when measured under the current CAFE system.

In a paper I just published, I provide a simple methodology to determine whether potential EPA GHG standards would deliver emission reductions equal to or greater than the California standards if applied to the nationwide fleet.

A quick summary of my results are that the national standard would have to result in a combined fleet average of about 264.9 grams of CO2 equivalent per mile in model year 2015. For comparison purposes, this level would result in a CAFE standard level of about 33.7 mpg, if the EPA GHG standards exist to ensure that low cost, non-CO2 GHG reductions are achieved through air conditioning improvements. If the EPA standards did not exist, the CAFE level would have to be raised by about 1.1 mpg to make up for the fact that the CAFE program does not account for air conditioning operations.

My methodology is describe in more detail in the full paper but is summarized below:

The equivalent GHG emissions value for the combined national fleet can be derived by taking a simple arithmetic average of the California PC/T1 (cars and light trucks) and T2 (heavier light trucks) standards, each one weighted for the proportion of PC/T1 and T2 vehicles forecast to be sold nationwide.  As an example, for model year 2015 (MY2015), the calculation is as follows:

((59.45%) x (213 g/mile)) + ((40.55 %) x (341 g/mile)) = 264.9 g/mile

The market shares are from the US DOE, Energy Information Administration's official forecast (Annual Energy Outlook 2009) which estimates 59.45 percent cars and 40.55 percent light trucks by calendar year 2016.

We present two illustrative calculations. The first assumes automakers do not make use of the air conditioning credits under the EPA GHG program or the flex fuel vehicle (FFV) credits under the CAFE program. For this calculation, the equivalent level in MPG terms is:

[(8,887 g/gallon) / ((264.9 g/mile) - (1.9 g/mile))] = 33.8 mpg

However, we believe this scenario is highly unlikely. Both air conditioning credits and FFV credits are very inexpensive compliance options. The calculation to convert the MY2015 national GHG equivalency level of 264.9 g/mile to a corresponding CAFE level would then be:

[(8,887 g/gal) / ((264.9 g/mile)-(1.9 g/mile)+(8.4 g/mile))] + (1.0 mpg) = 33.7 mpg