汽车对全球升温长期影响超飞机

近期发表在《环境科学与技术》上的一项研究论文指出，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。这项研究是由奥地利和挪威的一组科学家进行的，他们在研究中对比了各种交通工具排放的气体对全球变暖产生的短期和长期影响。

研究发现，按单个乘客每公里排放的二氧化碳量来比较，驾车出行比乘机的排放量要高；而且，由于二氧化碳在空气中滞留的时间较长，由此对气候变化产生的长期影响也就更大一些。 在货物运输方面，等距离运送等量货物时，飞机对气温升高产生的影响是普通卡车的7到35倍，而船运产生的长期影响却是卡车25分之一。

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 adverse climate impact because airplanes strongly affect short-lived warming processes at high altitudes.

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 suite of climate chemistry models to consider the climate effects of all long- and short-lived gases, aerosols 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 automobile travel for every kilometer a passenger travels. The findings prove robust despite the scientific uncertainties in understanding the earth's climate system.

"As planes fly at high altitudes, their impact on ozone and clouds is disproportionately 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 remains 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 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. Shipping on the contrary exerts 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 soot. Currently they also emit relatively large amounts of sulfur 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 offsets the warming. And because of the large volumes of goods traded by ship, global trade actually counteracts 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 pollutants 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 sector is actually to minimize the demand for transport."