Contrary to usual practice, well begin with the punch-line: less than 4/1,000ths of a degree Celsius. Thats how much warming might be spared half a century from now thanks to Europes decision, starting after the Kyoto treaty in the late 1990s, to switch more than 50% of its passenger cars to diesel.
https://secure.marketwatch.com/story/dieselgate-is-a-political-disaster-2017-02-14