A full-size pickup spews 12-to-13 tons of greenhouse emissions annually versus about eight tons for a mid-size car, says Glade Sowards of the Task Force on Global Warming [1] in Utah’s Division of Air Quality.

New federal regulations for diesel engines, which took effect in January, will help air pollution but do nothing to curb global warming.

"Catalytic converters and particulate filters help reduce that type of pollution," said Sowards. "But when it comes to CO2, or other greenhouse gases, they're mostly coupled with fuel consumption. The new diesel fuel will not reduce greenhouse gases."