Climate Forcing from the Transport Sectors

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-01, Vol.105 (2), p.454-458
• Main Authors: Fuglestvedt, Jan, Berntsen, Terje, Myhre, Gunnar, Rypdal, Kristin, Skeie, Ragnhild Bieltvedt
• Format: Article
• Language: English
• Subjects: Aerosols; Air Pollutants - analysis; Air Pollution - economics; Air Pollution - legislation & jurisprudence; Air Pollution - prevention & control; Air transportation; Atmosphere; Atmospheric aerosols; Aviation; Carbon Dioxide - analysis; Carbon Dioxide - chemistry; Carbon Dioxide - economics; Carbon dioxide emissions; Climate; Climate change; Conservation of Energy Resources - economics; Conservation of Energy Resources - legislation & jurisprudence; Conservation of Energy Resources - methods; Emissions; Environmental transport; Greenhouse Effect; Greenhouse gases; Kyoto Protocol; Methane; Models, Theoretical; Ozone - chemistry; Paleobotany; Physical Sciences; Pollutant emissions; Reference Values; Roads; Shipping; Transportation; Vehicle Emissions - analysis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0702958104

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 ≈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 ≈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.