photo by James Wang (Pylon757 on Flickr CC)

IPCC Climate scientists have already stated that air travel contributes to climate change though emitting CO2, water vapor, nitrous oxides, sulfate aerosols and soot. Each of these varieties of airplane emissions factor into global warming in different ways, including short and long-term warming effects.

A new scientific paper from Norway compares the climate impact of different modes of both passenger and freight transport. The study puts ocean and rail as having the lowest impact in terms of freight, with light trucks and air having the highest across the board. In the case of passenger travel, ‘rail, coach or two- and three-wheelers’ have the lowest impact in the short term, while air travel has the highest. For long-term global warming, the contribution of cars is equal to or higher than planes on a per passenger basis.

The reason this is so crucial is that the effects of different greenhouse gases play out in the atmosphere at a different speeds. CO2, released by all fuel-burning vehicles, can remain in the air for centuries, causing a gentle warming effect. By contrast, most other gases and impacts – such as the vapour trails and tropospheric ozone produced by planes at altitude – cause much more potent but shorter-lived bursts of warming.

–Guardian

If we are indeed at risk of reaching so-called ‘climate tipping points’, it follows that the short-term warming caused by other greenhouse gases/emissions are more of an immediate problem vis-à-vis global warming than CO2. This would put vapor, N2O, black carbon and methane reduction at the top of the urgency list, with CO2 as more long-term problem because it hangs around in the atmosphere for much more time.

Strangely, the level of sulfate aerosol emissions – polluting but actually cooling in terms of climate impact – is so high in ocean freight that it counteracts the warming caused by planes and cars. Yet the nitrous oxide-rich smog and soot from ship engines are a serious human health hazard. It has also been estimated that cargo ships currently produce 30% of the world’s nitrogen-oxide emissions, a powerful greenhouse gas.

Confused? Oh well, at least the CrCri, the first all-electric four-engined aircraft has recently made its first flight.

For more on the subject check out the study, entitled ‘Specific Climate Impact of Passenger and Freight Transport’ in the journal Environmental Science and Technology and the following Guardian blog:

The surprisingly complex truth about planes and climate change

Additional resources:

Water vapor and global warming