I think you must mean electric vehicles, right? Otherwise your statement applies equally well to saying there’s no difference in the city between a Focus and an Excursion.
Don’t hybrids utilize the braking energy to recharge the batteries? Isn’t that “free (no added pollution created) energy” in a sense, since it would have simply been dissipated as heat if it hadn’t been converted?
Philster
What the heck does this mean?
The only way I can imagine this could possibly make sense is that you’re saying that because only a finite amount of fossil fuels exist, then there is a finite amount of CO2 that can be released by burning fossil fuels. Sure, that is technically true, but has absolutely nothing to do with environmental harm. After all you could burn a small amount of fossil fuel each year until it’s all gone without any environmental harm at all, so the rate it’s used each year most definitely does matter, and efforts to improve fuel economy most certainly do have an environmental and public health benefit.
And as far as non-greenhouse pollution goes, there most certainly is not a set amount of pollution. ‘Burning’ a gallon of gasoline by sending it through a reformer and then to a fuel-cell produces almost no nitrogen oxides or particulates, whereas pouring a gallon of gasoline onto your driveway and adding a match will create quite a lot of nasties. Or, I suppose you could just let it sit uncovered until it evaporates, which creates few nitrogen oxides or particulates, but does put a whole lot of carcinogenic and smog-causing organic compounds into the air.
Oh, and related to fuel economy, you need to make sure you’re comparing apples with apples – particularly, don’t compare what you’ve measured with your personal vehicle to EPA’s estimate.
We use the saying YMMV for a reason, you know.
The hybrids don’t do anything special to the fuel they burn above and beyond any other vehicle. And the change in rate of consumption isn’t so drastic over other thrifty vehicles that you could demonstrate any effect on the ‘environment’. It ain’t significantly slowing down the rate at which we pour CO2 into the envrionment. Oh sure, a mass exodus from 25mpg cars to 80mpg cars world wide, but let’s no go gaga over hybrids cutting down on the total sum of pollution.
In the end, the gist of the problem is that we are going to blow through X amount of fossil fuels in a very short time. And should we stretch that very short time out by a few years, it wouldn’t do squat for the environment. Essentially, hybrids are good at moving pollution from one place to another.
You just seem to be repeating what you said earlier, after it has been refuted. 
You DO know that not all air pollution is permanent, right? The smog comes down when it rains. There isn’t “X” amount of cumulative smog that’s going to be in the air at a certain date in the future. Cleaning up the air is a matter of reducing the rate at which smog is produced.
IIRC, the reason you can’t use a catalytic converter with regular diesel has to do with the high sulphur content of the fuel. The automakers just fought a long, nasty battle with the oil companies over this. Automakers wanted the sulphur out, the oil companies didn’t. Eventually, the automakers won, and this is going to make it easier for them to install pollution control equipment on diesels (which, up until recently, had been pretty much unregulated as far as their emissions went).
Okay, educate me. Carbon Dioxide build up is temporary?