it's actually a pretty simple to figure out carbon footprint for gas powered cars. Gasoline is just a bunch of carbon atoms loosely linked together. You add heat, you add oxygen, and the carbon molecule bonds break in favor of bonding with oxygen to form carbon dioxide/monoxide, and release energy in the process. That's how combustion works. None of the carbon is destroyed in the process, all of the gasoline just gets converted into a gas; a greenhouse gas. Its why cars are the largest source of emissions in the US.
All of that is cut in an EV. With renewable energy sources there doesnt have to be any greenhouse emissions with EV's.