The surprisingly complex truth about planes and climate change | Duncan Clark | Environment | guardian.co.uk
If you'll forgive an extension to the "frying the planet" metaphor, generating global warming with CO2 is equivalent to slow-cooking the earth in a cast-iron skillet, whereas cooking the planet with vapour trails would be more like flash-frying it in an extra-hot wok.[From the comment section of the above article] | guardian.co.uk
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According to the paper, if we focus just on the impact over the next five years, then planes currently account for more global warming than all the cars on the world's roads – a stark reversal of the usual comparison. Per passenger mile, things are even more marked: flying turns out to be on average 50 times worse than driving in terms of a five-year warming impact.
If we shift to a 20-year time frame, things look completely different. The short-term impacts have largely died down and the plane looks considerably better – helped along by a quirk of atmospheric chemistry which sees nitrous oxide pollution from the aircraft engines causing cooling during this period by destroying methane in the air. The paper even suggests that for any time frame longer than 20 years, flying is typically greener per kilometre than driving (although when I phoned to check this, one of the authors of the report confirmed my suspicion that this isn't true in Europe, where fuel-efficient cars are more popular).
Of the various forms of transport examined by the researchers, shipping is the other one most markedly affected by short-term climate impacts. Here, however, everything is in reverse because the major short-term effect of shipping is sulfate aerosol pollution. While they remain in the air, these aerosol particles bounce sunlight away from the earth and therefore cause cooling rather than warming. The extent of this effect is amazing: if I'm understanding the numbers correctly, over a five-year time frame the world's ships cause enough cooling to offset the total warming caused by every car, plane and bus combined.
Even over a 20-year time frame, shipping pollution still contributes an overall cooling effect – as do electric trains, due to the aerosol pollution kicked out from coal-fired power stations. This throws up a tricky issue for policy makers and industry. If we clean up some kinds of air pollution for the benefit of environmental and human health, then we stand to significantly accelerate global warming in the near-term.
Cactiform seems to have interpreted the logic of this paper perfectly. Having looked at the paper,it does indeed claim tha SO2 pollution causes global cooling, and that coal power stations are therefore [are] helping to stop global warming.Specific Climate Impact of Passenger and Freight Transport - Environmental Science & Technology (ACS Publications)
High SO2 emissions notably from the electricity produced in coal fired power plants lead to a strong cooling from sulfate aerosols.
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That there is a large potential for a cooling influence is sort of evident in the IPCC figure about the present sulfate distribution--most is right over China, for example, suggesting that the emissions are near the surface--something also that is, so to speak, 'clear' from the very poor visibility and air quality in China and India. So, the quick, fast, cheap fix is to put the SO2 out through tall stacks. The cooling potential also seems quite large as the plume would go out over the ocean with its low albedo--and right where a lot of water vapor is evaporated, so maybe one pulls down the water vapor feedback a little and this amplifies the sulfate cooling influence.
I have been known to point out that if Obama's newly appointed science czar wanted to put vast amounts of sulfur dioxide into the air, that the government needen't spend any money to do it - they could merely pull the sulfur controls off the coal-fired plants:)
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