The best thing about the Prius is that it achieves its high fuel economy without sacrificing size or performance and, most importantly for global warming, without being a diesel. There seems to be a lot of confusion on this point in the comments section of Part One, so let me elaborate.

Bottom Line: If you care about global warming, don’t buy a diesel car (certainly not in this country), and if you must buy a diesel, only get a new one with a very good particle trap. [Does this mean that Europe’s massive switch to diesel was not good for the climate? In a word,”probably.“]

First, diesel fuel has a considerably higher carbon content than gasoline, so burning a gallon of diesel emits 22.2 pounds of CO2 vs. 19.4 for gasoline (see here). A diesel car with the same mpg as a gasoline car would have considerably higher carbon dioxide emissions per mile. [This is offset one third by the fact that diesel has fewer upstream emissions, which, if I did the math right, takes total life-cycle CO2 emissions from a gallon of diesel to 25.8 pounds vs. 24.2 for gasoline (see here).]

diesel.jpgSecond, and more importantly, we have known for a number of years that black carbon (BC) or small soot particles are a major greenhouse gas — and that diesel engines are a major source of BC. A March 2008 review article published in Nature Geoscience, (subs. req’d, abstract below), “Global and regional climate changes due to black carbon,” found that BC may be as much as 55% as potent in total greenhouse warming as CO2.

In October, the House held “a hearing to examine the climate change and other impacts of black carbon emissions” (testimony and transcript here). Dr. Mark Jacobson, Co-founder and Director of the Atmospheric Energy Program at Stanford University’s Department of Civil and Environmental Engineering, testified directly on how BC emissions significantly reduce the climate benefits from diesel cars (here):

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