Global temperature responses to current emissions from the transport sectors.

Transport affects climate directly and indirectly through mechanisms that cause both warming and cooling of climate, and the effects operate on very different timescales. We calculate climate responses in terms of global mean temperature and find large differences between the transport sectors with respect to the size and mix of short- and long-lived effects, and even the sign of the temperature response. For year 2000 emissions, road transport has the largest effect on global mean temperature. After 20 and 100 years the response in net temperature is 7 and 6 times higher, respectively, than for aviation. Aviation and shipping have strong but quite uncertain short-lived warming and cooling effects, respectively, that dominate during the first decades after the emissions. For shipping the net cooling during the first 4 decades is due to emissions of SO(2) and NOx. On a longer timescale, the current emissions from shipping cause net warming due to the persistence of the CO(2) perturbation. If emissions stay constant at 2000 levels, the warming effect from road transport will continue to increase and will be almost 4 times larger than that of aviation by the end of the century.