Can we reduce greenhouse gas emissions from running our cars and light trucks by 80 percent by 2050? According to a new report by the National Academy of Sciences, the answer is yes, but it will be difficult, and it can only happen with a set of strong, sustained, and adaptive public policies.

For the past two years, I’ve had the privilege of serving on the NAS Committee that produced this new report. We concluded that four fuel and vehicle pathways can help us meet our goals: (1) continuous improvements in the efficiency of conventional gasoline-powered cars, (2) biofuels, (3) hydrogen and fuel cell vehicles, and (4) plug-in electric vehicles. Each of these could dramatically reduce greenhouse gas emissions over time, but each also faces enormous challenges.

I was surprised to learn how much progress has recently been made in plain old efficiency, increasing how far you can go on a gallon of fuel, and how much more can still be accomplished. The same technologies that can improve efficiency for gasoline and diesel-fueled vehicles also can improve efficiency for alternative fuel vehicles.

All the alternative pathways must reduce their costs and improve their performance to compete with conventional vehicles and fuels.  In addition, each alternative fuel pathway faces its own challenges.  For biofuels, the key barrier is competition for land – whether to use it to grow crops that can be made into biofuels or to grow other crops or for other purposes. For hydrogen, the key barrier is the “chicken and egg” problem of coordinating the build-out of a whole new hydrogen fueling infrastructure with deployment of fuel cell vehicles. For plug-in electrics, the key barrier is the technical challenge of designing a battery that fits in a vehicle doesn’t take very long to re-charge, and can go a reasonable distance on a single charge, all at an affordable cost.

After extensive analysis of technical potential, costs, and policy options, the NAS concluded that we should continue to pursue all four pathways. At this point it would be a mistake to write off any of them.

Seventeen percent of U.S. greenhouse gas emissions come from light-duty vehicles. Because the benefits of greenhouse gas reduction are public benefits, market forces alone will not be sufficient to achieve the ambitious goal of reducing emissions from cars and light trucks by 80 percent by 2050. We need strong public policies to drive the necessary innovation and pull low-emitting vehicles and fuels into the marketplace.

Continuing to strengthen vehicle fuel economy and greenhouse gas emission standards is of paramount importance. So are policies such as carbon pricing, to ensure a low-emitting fuel supply. Public and private research, development and deployment are critical as well. We can do this, but only with a sustained national effort.