realistic clean air approach

There are a few approaches to clean up our air being discussed in the public forum, but each has significant flaw:

charging a $10,000 tax on gas-hogging SUVs and a $10,000 tax rebate for gas-sipping hybrids would never work because (a) it's not the class of vehicles that pollutes, it's their consumption (mpg or L/100km), and (b) north-american carmakers would find all the little loopholes that their friendly/bankrolled legislators left in there for them anyway;

setting meaningless 40-year targets that everybody knows are completely unenforceable;

tax fuel at the pump for the cost of sequestering the corresponding amount of pollutants it would release, but any econo-political leverage mechanism (e.g., to ease the burden on politically-strategic industries suddenly unsustainable) would no doubt require at least a few hundred or so dedicated bureaucrats to manage, and last I heard methane was still on the "bad" list.

Here's my idea that I think everybody could accept: a proportional tax program on new car sales with progressive targets. Say 9.0 L/100km is the mark for 2008. Cars consuming more than that (on the label) are flat-taxed relative to that, and those that consume less than that get a flat credit relative to that. Then every year the target gets lower: 8.8 in 2009, 8.5 in 2010, 8.1 in 2011, 7.6 in 2012, 7.0 in 2013 etc. Competition (and profit margins) under these more-representative-of-true-cost conditions would shift the auto-industry's attention to more efficient engines rather quickly. The progressive target would also give everybody - the auto-industry, investors, the alternative technology industry and consumers - time to adjust.

Of course, the penalty/incentive amounts would have to be important enough - other parents looking for daycare spaces can attest to the ineffectiveness of symbolic economic measures...