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, 105 (2), 454-8

Climate Forcing From the Transport Sectors


Climate Forcing From the Transport Sectors

Jan Fuglestvedt et al. Proc Natl Acad Sci U S A.


Although the transport sector is responsible for a large and growing share of global emissions affecting climate, its overall contribution has not been quantified. We provide a comprehensive analysis of radiative forcing from the road transport, shipping, aviation, and rail subsectors, using both past- and forward-looking perspectives. We find that, since preindustrial times, transport has contributed approximately 15% and 31% of the total man-made CO2 and O3 forcing, respectively. A forward-looking perspective shows that the current emissions from transport are responsible for approximately 16% of the integrated net forcing over 100 years from all current man-made emissions. The dominating contributor to positive forcing (warming) is CO2, followed by tropospheric O3. By subsector, road transport is the largest contributor to warming. The transport sector also exerts cooling through reduced methane lifetime and atmospheric aerosol effects. Shipping causes net cooling, except on future time scales of several centuries. Much of the forcing from transport comes from emissions not covered by the Kyoto Protocol.

Conflict of interest statement

The authors declare no conflict of interest.


Fig. 1.
Fig. 1.
Historical development in emissions and radiative forcing for CO2 from the transport sector. (A) Development in CO2 emissions from the various transport subsectors and the fraction (right axis) of total man-made CO2 emissions (excluding land use changes). (B) Development in RF due to CO2 from these sectors.
Fig. 2.
Fig. 2.
Radiative forcing since preindustrial times, by substance and transport subsector. (A) Global mean RF (mW/m2) for 2000 due to transport, relative to preindustrial times. (B) Global mean net RF (including all components in A) for 2000 due to transport, relative to preindustrial times, per sector. Uncertainty ranges are given for 1 SD. (BC and OC from off-road vehicles and equipment are not included but are estimated at 13 and −1.1 mW/m2, respectively, for 1996 emissions.)
Fig. 3.
Fig. 3.
Integrated radiative forcing of current emissions, by substance and transport subsector, over different time horizons. (A) Integrated global mean RF (mW/m2 yr) due to 2000 transport emissions, time horizon H = 100 years. (B) Integrated global mean net RF per sector due to 2000 transport emissions, normalized to the values for road transport for various time horizons (20, 100, and 500 years). Uncertainty ranges are given as 1 SD.

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