That conclusion is odd. It mentions that not all electricity comes from fossil fuels, then immediately launches into a calculation that assumes all of your electricity comes from fossil fuels. It also completely ignores the fact that different fuels emit different amounts of CO2 for the same amount of energy. This one actually supports their conclusion; as far as I can see, gasoline produces less CO2 for a given amount of energy than natural gas, and way less than coal. There's also the nontrivial energy and thus CO2 emissions needed to extract, refine, and deliver gasoline, and of course that comes into play (albeit less so) on the electricity side as well. I think that part of the article glosses over these details a little too much.