Car versus plane: travel and the climate change debate
Which is worse for global warming: travelling by car or by plane? According to the results of an EU-funded study, car travel increases global temperatures more than an air travel for the same journey but only in the long term. Travelling by plane, on the other hand, adversely affects short-lived warming processes at high altitudes. The findings are part of the QUANTIFY ('Quantifying the climate impact of global and European transport systems') project, which was funded EUR 8.39 million under the 'Sustainable development, global change and ecosystems' Thematic area of the Sixth Framework Programme (FP6).
Published in the journal Environmental Science & Technology, the results are part of an ambitious research programme that incorporated the expertise of 41 participants and 6 associated members from 17 European countries as well as China, India and the US. Together, their work under QUANTIFY focused on the impact of air, sea and land traffic (of both the European and global transport systems) on the Earth's climate, with particular reference to the effects of greenhouse gases, emissions of ozone precursors and particles, contrails and ship tracks. The ultimate goal was to provide forecasts and other policy-relevant advice to governments and international bodies.
For the researchers involved in the current study, it was the first time a particular series of climate chemistry models were used to compare the climate effects resulting from different modes of global transport. Importantly, in addition to carbon dioxide (CO2), the study considered the effects of all gases (both long- and short-lived), aerosols and cloud effects.
The team found that in the long run driving a car, on average, increases global temperatures more than if you were to make the same long-distance journey by air. However, for the first few years after the journey, travel by air increases global temperatures four times more than car travel.
The lead author of the study, Dr Jens Borken-Kleefeld from the International Institute for Applied Systems Analysis in Austria, explained that since planes fly at high altitudes, their impact on ozone and clouds is short lived but disproportionately high. The researchers are uncertain of the exact magnitude but believe the net effect is a strong (albeit short-term) temperature increase.
'Car travel emits more CO2 than air travel per passenger kilometre. As CO2 remains in the atmosphere longer than the other gases, cars have a more harmful impact on climate change in the long term,' Dr Borken-Kleefeld explained.
The team of researchers from Austria and Norway also found that transporting goods by plane will increase global temperatures up to 35 times more than moving the same goods in a lorry over the same distance. Rather surprisingly, in the long run shipping exerts 25 times less warming, and even cools in shorter periods.
'Ships contribute to global warming through CO2, ozone and soot. Currently they also emit relatively large amounts of sulphur dioxide which forms sulphate particles in the atmosphere. Those particles cool the planet by reflecting solar radiation back into space,' explained co-author Dr Jan Fuglestvedt from the Centre for International Climate and Environmental Research (CICERO) in Norway.
Dr Fuglestvedt added that in the first few decades after a shipment, the cooling effect more than offsets the warming. Since huge volumes of goods are traded by ship, international trade actually counteracts some of the temperature increases triggered by global passenger travel. He warned, however, that 'in the long term all means of motorised transport add to global warming'.
The QUANTIFY project ran from March 2005 to February 2010. Other achievements include the emission inventory database, a summer school, a series of international conferences, and web portal eLearning activities.