Transportation is a fairly wide ranging thing, including billions of cars as well as trucks, buses, trains, aircraft, ships all burn various forms of hydro carbons. Scientific estimates put transportation at about 1/3 of current human emissions. But solid efforts are being made to reduce this, major car makers are moving to electric VW plan to do this in the next few years a number of others are not far behind them. An all electric plane has already flown the English Channel. A global shift to electric cars could have a very solid effect on our global Co2 emmissions, as well as being cheaper to run and needing far less maintainence than a petrol powered car.