In a report published last month, the eight international scientists put aviation’s total contribution (‘radiative forcing’) in 2005 at 4.9%.
This is well over the 3% these same authors came up with two years ago in the IPCC’s Fourth Assessment Report on the state of global warming.
This figure, which comes in a total ‘bandwidth of 2-14%’, is more consistent with the figure used by environmental groups. In its report Clearing the Air published in 2006, T&E put the figure at 4-9%.
There are two main reasons for the scientists’ upward revision. For the first time they include the impact of cirrus clouds in their central estimate, and they base their calculations on 2005 operations data, not 2000 which was used in the 2007 assessment. As passenger traffic by air grew by 22% between 2000 and 2005, and 38% between 2000 and 2007, the revised figure of 4.9% might still be on the conservative side.
The average annual passenger traffic growth rate was 5.3% between 2000 and 2007, resulting in an increased use of fuel in aircraft of 8.4%.
T&E policy officer Bill Hemmings said: ‘The mathematical system used to calculate the contribution of aviation to climate change in the Fourth Assessment Report was seriously flawed, and it’s good to see that this has now been corrected so we get a clearer picture of the true impact’.
‘It is now up to decision-makers to take serious note of these numbers and work to limit the growth in aviation. This December’s climate summit in Copenhagen offers a perfect opportunity for this to happen.’