Economists, like politicians and other activists, often engage in sterile debates about picayune issues instead of engaging with real issues.

It appears that the Cato authors have misstated the first statistic. Consultation of the cited source seems to show not that an increase in efficiency leads to a 20 percent jump in vehicle miles traveled, but that roughly 20 percent of total energy savings from efficiency gains are lost to increased travel. That's quite a different point, implying that efficiency gains could have a significant impact on emissions.

The second statistic applies to a different argument: that because emissions per gallon of gas vary substantially by the type and age of an automobile, a gasoline tax is a very inefficient way to reduce emissions. I absolutely agree that a direct tax on emissions would be preferable to a proxy levy on gasoline, but an emissions tax is not without its costs. Increasing gasoline taxes requires only the passage of legislation, while levying an emissions tax requires the creation of government mechanisms for auditing vehicle emissions and miles traveled--a more expensive, intrusive, and time-intensive solution.

The largest omission that I see in the Cato piece, however, is the lack of consideration of the potential for substitution away from driving in the wake of higher gasoline taxes. Consumers would not simply respond to higher gasoline costs by purchasing more efficient vehicles. They would also drive less with existing vehicles, carpool, use mass transit, walk or ride a bicycle, or telecommute. Transportation mode helps determine the shape and size of the spatial economy, and if negative externalities imply overconsumption of automobile trips, then they also imply an economic space over-dependent on use of a personal automobile. In the long run, then, higher gasoline prices should change the look of neighborhoods and cities, increasing the feasibility of alternate transportation modes, and facilitating substitution between cars and other means of getting around.

It's possible, maybe probable, that substitution away from driving might entirely counteract the rebound effect mentioned above.

However, it would have no effect at all on climate. The miniscule reduction of emissions that might, might, result from all these gyrations and socio-economic disruption would be undetectable on a global scale even in the very rosiest of cases.

That's just stupid . . . or perhaps it's instrumental. It isn't the climate that concerns these meddlers, it's personal freedom. They want to stamp it out. Consider this revealing comment: "if negative externalities imply overconsumption of automobile trips, then they also imply an economic space over-dependent on use of a personal automobile." If personal automobiles didn't emit gasses these wankers would still object to them. Emissions are merely an excuse to impose their crabbed world view on humanity.

I often feel as if I'm listening to creationist arguments or alchemist explanations of physical reality when I hear the silly things that economists debate. They have no idea what they are talking about, but they talk about it in the patois of their trade. It makes no sense but it has the form of sensible debate. Their discourse is content free.