Climate Crisis: Is Diesel the Answer?

With the arrival of Volkswagen's 50-mile-per-gallon, diesel-powered Jetta TDi next year, people are sure to wonder why all cars aren't running on diesel. That's how Europe does it. That's how big-rig truckers do it. Why not everyone?

A recent Green Lantern column at Slate looks at this question, and comes up with a mixed review.

First, let's look at the difference between gas and diesel. Diesel is less refined than gas, and it takes more crude oil to make a gallon of diesel. This mean's diesel's energy density is higher (more MPG), but it also cranks out more greenhouse gas when burned. The tradeoff: 40 percent more miles per gallon for 15 percent more greenhouse gas. In the end, "diesel cars usually emit less of these gases per mile driven."

Traditionally, diesel exhaust has been packed with "nasty particulates," but advances in diesel refining techniques and engine technology have pretty significantly reduced these. However, the new refinement processes require more crude oil to make a gallon of diesel, and the complex new engines "require more energy and materials to manufacture."

Also, despite the advances, diesel emissions remain dirtier than gasoline's. And according to a 2002 Stanford study, "even if all diesels were designed to meet California's emissions standards, diesel cars could still warm the globe more than petrol cars over the next half-century." Of course, that's because not all greenhouse gasses are created equal.