Global warming is the big deal these days, and people are casting about, asking, what kind of car has the lowest greenhouse gas emissions? I have the answer.

Here is a table, derived from data obtained from Wang and others at Argonne National Laboratory. These emissions are totals of all greenhouse gases, but expressed in terms of grams of CO2 per mile traveled. The numbers are for a car that gets 50 miles per gallon, normalized to "gasoline equivalent." For example, the CNG car burns the same BTUs of CNG per mile as the gasoline car does.

Gasoline or hybrid....... 236 grams CO2 per mile

Diesel....................... 228

Compressed NG.......... 261

Ethanol (E85).............186

Biodiesel................... 116

Electric (100 mpg)...... 264

Remember, these cars all use about the same amount of energy per mile. The electric car is the very worst of the bunch. (Which means that plug-in hybrids, PHEVs, which use electricity are also worse than all the others.)

You should notice that the electric car is rated at "100 mpg" instead of 50. This is necessary to even out the energy use. You see, electric cars are always rated at the point of charging. So about half of their energy use, from the power plant to the battery charger, is neglected. Thus the "100 mpg" electric car is really a 50 mpg car. If I don't make this adjustment, then the EV's CO2 is TWICE as high as the number above.

Remember, the numbers are for cars of equivalent mpgs (or energy use). Diesels will do even better than above because they usually get much better mileage than the others. In fact, this applies similarly to electric cars-- If a gas or diesel car is converted to an EV, assuming state-of-the art parts, the EV will actually use less energy than the others, and then it does emit slightly less CO2. No such EVs exist today, the really good ones were all crushed by GM. (The EV1.) The best available EV today is probably the RAV4 EV which is rated at 114 miles per gallon equivalent, and puts out 232 grams of CO2 per mile. In order for an EV to score better than a TDI getting 50 mpg on biodiesel, it would have to have a mileage rating greater than 228 miles per gallon.

I mentioned that the data comes from Wang at ANL. The data are available on-line, it's called the GREET model. I took the information from the

www.auto.xprize.org web site. You might want to look into this. They are intending to award over $10 million to the best 100 mpg cars, based on a race in 2009.

Ernie Rogers