content: SpaceX's BFR uses propellant(methane) and oxidizer(liquid oxygen) so there are no fossil fuels, no pollution, no climate change. You can even make methane using the sabatier reaction , you just need solar power and you are good to go.  methane(CH4) is used because it gives a good ISP but the fuel methane can be made on mars, because mars has water ice and C02 in the atmosphere.