I’ve been trying to find out something about aircraft emissions in the light of the Airport Authority Hong Kong (AAHK)’s consultation paper on the proposed third runway. According to Wikipedia, in 1992 CO2 emissions from aviation were estimated at 2% of global anthropogenic emissions. By 1999 the IPCC were claiming that the total impact of aviation was 2-4 times the direct emissions of CO2, not including the effect of cirrus cloud enhancement from contrails. NASA’s Glenn Research Center currently states on its website that, “Aircraft produce up to 4 percent of the annual global CO2 emissions from fossil fuels near the Earth’s surface as well as at higher altitudes (25,000 to 50,000 feet)”. Meanwhile, in 2009, an analysis produced by Stanford University in Palo Alto maintained that commercial airline flights are responsible for 4-8% of surface global warming, and that contrails over the Arctic are responsible for no less than 15-20% of warming. Apparently, previous studies have only estimated the impacts of commercial aviation, whereas this study is the first to use actual emissions data produced between 2004-2006:
Finally, a recent study from the German Aerospace Centre states that although aircraft are responsible for 3% of annual CO2 emissions from all fossil fuels, their contrails, which form cirrus clouds, actually have a greater impact on the climate than their CO2 emissions.
I’m not able to assess the accuracy one way or another of these studies, but it seems as if the estimates of the impact that aircraft have upon the climate are steadily rising. Hardly surprising then that there is no mention of it in AAHK’s consultation paper!