"As large as California is, however, it produces only 6.5 percent of America's man-made CO₂ emissions, and the U.S. accounts for 25 percent of the world total. Moreover, California's privately owned vehicles account for 40 percent of the state's CO₂ output. Multiply the percentages, and you get a global man-made CO₂ reduction of well under one percent, even if private driving in California were completely banned."