Driving alone in a car increases global temperatures in the long run more than making the same long-distance journey by air according to a new study. However, in the short run traveling by air has a larger adverse¹ climate impact because airplanes strongly affect short-lived warming processes at high altitudes.

一项新研究指出，在行程距离相同的情况下，驾车出行对全球升温带来的长期影响要超过乘飞机出行。不过，从短期来看，飞机对气候的不利影响要更大一些，因为飞机在高空中飞行时对云层和臭氧层造成破坏从而导致短时的升温效应。

The study, published in the journal Environmental Science & Technology by a team of researchers from Austria and Norway, compares the impacts on global warming of different means of transport. The researchers use, for the first time, a suite² of（一系列） climate chemistry models to consider the climate effects of all long- and short-lived gases, aerosols³（气溶胶，喷雾器） and cloud effects, not just carbon dioxide, resulting from transport worldwide.

In the long run the global temperature increase from a car trip will on average be higher than from a plane journey of the same distance. However, in the first years after the journey, air travel increases global temperatures four times more than car travel. Passenger trains and buses cause four to five times less impact than automobile⁴ travel for every kilometer a passenger travels. The findings prove robust⁵（强健的，粗野的） despite the scientific uncertainties⁶ in understanding the earth's climate system.

"As planes fly at high altitudes, their impact on ozone⁷ and clouds is disproportionately（不成比例地） high, though short lived. Although the exact magnitude is uncertain, the net effect is a strong, short-term, temperature increase," explains IIASA's Dr Jens Borken-Kleefeld, lead author of the study. "Car travel emits more carbon dioxide than air travel per passenger kilometer. As carbon dioxide remains⁸ in the atmosphere longer than the other gases, cars have a more harmful impact on climate change in the long term."

The research also showed that when it comes to freight（运输，海运） transport, moving goods by planes will increase global temperatures between 7 to 35 times more than moving the same goods the same distance in an average truck. Shipping⁹ on the contrary exerts（发挥，运用） 25 times less warming in the long run, and even cools on shorter time scales.

"Ships contribute to global warming through carbon dioxide, ozone and soot¹⁰（煤烟，烟灰） . Currently they also emit relatively¹¹ large amounts of sulfur¹² dioxide which forms sulfate particles in the atmosphere. Those particles cool the planet by reflecting solar radiation back into space," says co-author Dr Jan Fuglestvedt from CICERO. "In the first decades after a shipment, the cooling effect more than offsets¹³ the warming. And because of the large volumes of goods traded by ship, global trade actually counteracts¹⁴ some of the temperature increases caused by global passenger travel. However, in the long term all means of motorized transport add to global warming."

The study concluded that as climate change acts at various time scales, it is important to have policies to reduce both the air pollutants¹⁵ that have strong, short-term impacts and the long-lived gases that lead to long-term warming. In addition, Dr Borken-Kleefeld argues: "A comprehensive strategy to tackle climate change caused by the transport sector¹⁶ is actually to minimize the demand for transport."