I'm definitely not a Chemtrails person!
Anyway, the paper to which the New Scientist article refers is this one:
'Reducing the climate change impacts of aviation by restricting cruise altitudes'
Transportation Research Part D: Transport and Environment, Volume 7, Issue 6, November 2002, Pages 451-464
Victoria Williams, Robert B. Noland and Ralf Toumi
I have an electronic copy of the paper on my screen.
To clarify, the calculated increased fuel burns are the result of a complex simulation using a reorganized air traffic control mathematical simulator (RAMS) for Europe only (i.e. it may be weighted towards short haul flights and it also appears to allow for a reorganization of the air traffic management structure). They concede that their simulations produced variable outputs depending on the parameters, including a 7.2% increase under some circumstances. 3.9% is the weighted mean.
Note that the conclusions do not advocate that such a reorganisation of air traffic should be undertaken, just that the results are interesting:
'The results presented here indicate that a strategy to avoid the production of contrails by restricting cruise altitude could provide a net benefit to climate, despite the associated increase in CO2 emission. The analysis suggests that the implications for controller workload present the most likely operational obstacles to such a scheme and that reconfiguration of airspace would be required to mitigate the impacts.'
The study of the effects on surface temperature of Sept 11th is this one:
Nature Volume 418(6898) 8 August 2002 p 601
Climatology: Contrails reduce daily temperature range
Travis, David J.*; Carleton, Andrew M.†; Lauritsen, Ryan G.*
Again, I have a copy.
They conclude:
'Our findings indicate that the diurnal temperature range averaged across the United States was increased during the aircraft-grounding period, despite large variations in the amount of cloud associated with mobile weather systems (Fig. 2). We argue that the absence of contrails was responsible for the difference between a period of above-normal but unremarkable DTR and the anomalous conditions that were recorded.'
In other words, there was clear evidence that contrails affect short term surface temperatures. No conclusions were drawn about the impact on global warming, but it does not seem unreasonable to hypothesise that the contrails have some role to play, be it positive or negative in terms of anthropogenic heating.
With regard to the science, the Intergovernmental Panel on Climate Change (IPCC) studied the role of aviation in global warming in detail (and continue to do so). Their detailed report is here:
http://www.grida.no/climate/ipcc/aviation/index.htm
With regards to contrails they said in the summary (there is more detail in the report)
(
http://www.grida.no/climate/ipcc/aviation/007.htm#spm45 ):
4.5. Contrails
In 1992, aircraft line-shaped contrails are estimated to cover about 0.1% of the Earth’s surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth’s surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 in the reference scenario (Fa1), at a rate which is faster than the rate of growth in aviation fuel consumption.
This faster growth in contrail cover is expected because air traffic will increase mainly in the upper troposphere where contrails form preferentially, and may also occur as a result of improvements in aircraft fuel efficiency...The radiative effect of contrails depends on their optical properties and global cover, both of which are uncertain. Contrails have been observed as line-shaped clouds by satellites over heavy air traffic areas and covered on average about 0.5% of the area over Central Europe in 1996 and 1997.
4.6. Cirrus Clouds
Extensive cirrus clouds have been observed to develop after the formation of persistent contrails. Increases in cirrus cloud cover (beyond those identified as line-shaped contrails) are found to be positively correlated with aircraft emissions in a limited number of studies. About 30% of the Earth is covered with cirrus cloud. On average an increase in cirrus cloud cover tends to warm the surface of the Earth. An estimate for aircraft-induced cirrus cover for the late 1990s ranges from 0 to 0.2% of the surface of the Earth. For the Fa1 scenario, this may possibly increase by a factor of 4 (0 to 0.8%) by 2050; however, the mechanisms associated with increases in cirrus cover are not well understood and need further investigation.
To say that these scientists do not know what they are talking about on the basis of third hand information would seem to be somewhat naive. Read their reports first-hand (all IPCC reports are available online for example), then make a decision.
This is a serious issue for aviation. The vast majority of climate scientists now accept that some anthropogenic global warming is occurring (IPCC involves about 1000 experts from universities, research centres, business and environmental associations, and other organizations in approximately 120 countries). As a result, the pressure to see reductions of change-causing processes is going to increase in the future. Aviation would be well-advised to act in a pre-emptive manner rather than have regulation imposed upon it. Burying our collective head in the sand is an unwise policy, whether you believe in the science or not.
Apologies for the long post
DrDave