>According to the Union of Concerned Scientists, 20% of all emissions are tailpipe from cars. The only USC source I could find[1] says that 20% of US emissions

>According to the Union of Concerned Scientists, 20% of all emissions are tailpipe from cars. The only USC source I could find[1] says that 20% of US emissions are tailpipe emissions, but the question was about global emissions. Globally transport makes up 14% of emissions according to the IPCC.[2] [1] http://www.ucsusa.org/clean-vehicles/car-emissions-and-global-warming http://www.ucsusa.org/clean-vehicles/car-emissions-and-globa... [2] https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data#Sector https://www.epa.gov/ghgemissions/global-greenhouse-gas-emiss...