A new study into various transport sectors’ contributions to pollution reveals that road traffic is the worst offender. It causes more greenhouse gas emissions than aviation, which is the second-largest pollutor. By contrast, shipping has a cooling effect.
The study was carried out by Norwegian researchers at the Center for International Climate and Environmental Research (CICERO) of Oslo Univerity.
The researchers focused on four sectors: road transport, aviation, rail, and shipping. They calculated each sector’s radiative forcing (RF), which is the net warming effect calculated in the unit Watts per square meter (W/m2).
The reason that road transport tops the list is mainly the amount of vehicles on the roads and the smaller cooling effect from their emissions. The researchers have not yet looked at emissions per kilometre or per person at a certain distance using different transport modes.
The five researchers involved in the study say that since preindustrial times the transport sector has been responsible for 15 percent of the RF caused by man-made CO2-emissions and the road transport also seriously damagest the ozon layer.
If anything, the study’s outcome implies that more attention needs to be put on the fast growing road sector. “The road emissions of today will constitute three- fourth of the warming caused by transport over the next hundred years”, say the researchers.
Shipping is a different story altogether. This form of transport cools the climate because shipping emits large portions of the gasses SO2 and Nox, positive coolants. But, the researchers warn, the effect will diminish as time elapses, because SO2 and Nox don't hang around very long; “After a few decades, the long-lived CO2 will dominate, giving shipping a warming effect in the long run”, say the researchers. At the same time, both SO2 and NOx have other impacts that damage the environment. The two emissions are not covered by the Kyoto Protocol.
Aviation is second in the research because the researchers opted for a historical approach. The historical contribution from aviation emissions to global warming is more than doubled by the contribution from road emissions. “Over the next 100 years, today's road emissions will have a climate effect that is four times higher than the climate effect from today's aviation emissions”, the researchers say.
They add that the transport sector's contribution to global warming will continu to be high and they estimate that current emissions from transport are responsible for approximately 16 percent of the net radiative forcing over the next 100 years. The dominating pollutant is CO2, followed by tropospheric O3. The warming effect by rail emissions is negligeable compared to those by road transport and aviation.
The study, entitled "Climate forcing from the transport sectors", claims to be the first comprehensive analysis of the climate effect from the transport sector on a global scale.