If true, the case for carbon taxes would be seriously weakened, since transportation accounts for about 30 percent of energy-related CO2 emissions in the United States. Fortunately, drivers have many more options—and are thus more sensitive to price incentives—than these doubters claim.

Most of us could take fewer and shorter discretionary trips if fuel costs began to bite more. By avoiding excessive highway speeds, driving 60 rather than 70 mph, we could burn about 15 percent less gas. More of us in urban areas could and would use public transportation or carpools if the cost of driving alone increased enough. Over the longer term, during past oil crises and even in the early 2000s when gas prices were high, most of us have considered buying more fuel-efficient vehicles. Fed up with long commutes, some of us are even moving closer to work.

Rather than speculate about such matters, empirical economists have discovered that drivers are several times more sensitive to fuel tax hikes than to ordinary market fluctuations that drive up prices at the gas pump. (That may in part be because drivers realize taxes rarely drop back down.) A 2009 study determined that raising gasoline taxes just 10 cents per gallon (equal to a carbon tax of about $10 per ton of CO2) cuts automobile carbon emissions by about 1.5 percent. That’s not much, but a gasoline tax of $1, still well below European and Japanese norms, would have a real impact.

Their calculations may be conservative. Economists at the University of Ottawa estimated that British Columbia’s modest carbon tax, first imposed at a rate of C$10 per ton of CO2 in 2008, slashed gasoline demand more than 12 percent by the time it hit $25 per ton of CO2 a few years later. Over the first four years, they calculated, the provincial carbon tax reduced emissions from gasoline consumption by more than 3.5 million tons of CO2.

Carbon taxes will have to climb a lot higher to drive the world to a zero-carbon future, but these examples suggest that measures like the Energy Innovation and Carbon Dividend Act would have a major impact on transportation emissions in just a few years. Carbon fees are also better than most alternatives when it comes to this task. National fuel economy standards, for example, cost somewhere between six and 14 times more than carbon fees per ton of CO2 avoided, according to a 2013 analysis by researchers at MIT. That’s because they narrowly target only new vehicles, not existing vehicles or the behavior of drivers.