Transport sector increases its influence on climate

29 October 2009 Centre for International Climate and Environmental Research (CICERO)

Since pre-industrial times, transport in total has contributed approximately 10 percent of total net man-made warming in the year 2000. The dominating contributor to warming is CO₂, followed by tropospheric O₃. The sector is expected to increase its influence.

“In 2050, global warming due to transportation emissions may be three to four times larger than it has been till now”, research director Jan S. Fuglestvedt at CICERO said.

Scientists at CICERO Center for International Climate and Environmental Research – Oslo have calculated how transportation might contribute to global warming in the years to come. The study is performed within the EU project QUANTIFY - Quantifying the Climate Impact of Global and European Transport Systems, and these results are published in the journal Atmospheric Environment.

Traveling and trade

According to three out of four scenarios, the total net contribution from the transport sectors to total man-made warming will be 15 percent in 2050. The emissions are expected to increase also in other sectors. Transport will have a warming effect that is three to four times larger than the current effect.

Towards the end of the century, the contribution from the transport sector to man-made warming may be up to 20 percent. Also this number hides an enormous increase: The warming effect in absolute terms might be six to ten times larger than in 2000.

“More traveling and international trade drive the emission increase”, Fuglestvedt said.

Road transport

“Road transport gives the largest contribution and will most likely continue to do so in the future”, Fuglestvedt said.

CO₂ is the most important climate gas from road traffic. Scientists expect these emissions to increase, while they expect large reductions in the emissions of other gases, based on knowledge and assumptions about new technologies as well as known and expected future regulations.

The transport sector emits a range of gases and particles that affect the climate in many ways. Some of the emissions have warming effects, other lead to a cooling of the earth. Also the time scales vary: Emissions of CO₂ have effects that last for centuries, while other emissions are short-lived with lifetimes of only a few days.

Four scenarios

To calculate future warming effects, four different scenarios for emissions from the transport sectors are established. The scenarios imply different assumptions of economic development and population growth. There are also assumptions about factors like technology development, implementation of technology, regulations, and use of new fuels.

”A scenario based study shows the main patterns of possible future developments, given what we know today and different assumptions. We see that CO₂ is the most important greenhouse gas in the long term, but several other components and effects are also important. Some of these effects are very uncertain, especially those regarding aviation”, Fuglestvedt said.

Aviation, shipping, train

Following road transport, global aviation has the highest warming effect. In addition to CO₂, ozon, contrails and cirrus clouds are important contributors to this effect. But these processes are far more uncertain than the CO₂ effect and thereby the climate effect from aviation is more uncertain than the climate effect from road transport. Aviation might constitute 4 percent of global warming in 2050. This implies an effect that is 2.5 to 3.5 times larger than today.

Shipping has, in the beginning of this century, had a cooling effect on the global temperature due to emissions of SO₂. Regulations are expected to significantly reduce these emissions. Shipping is expected to have a net warming effect by the mid or end of the century.

The train sector is a small sector and has a small climate effect compared to the other sectors, also when emissions from production of electricity is included.

In the future, zero emission vehicles and new fuels will be introduced. These cause low direct emissions, but fuel production and electricity cause indirect emissions. According to the study, these indirect emissions have a warming effect that is only in the order of 10 percent of the effect from the sector’s direct emissions.

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