Sun 11 Oct 2009 – The International Air Cargo Association (TIACA) has challenged the findings of a recently published major study of aviation’s CO2 and non-CO2 impact on climate change. According to TIACA, the authors of the study had increased aviation’s previous contribution to climate change from 3% in the IPCC Fourth Assessment Report (AR4) to 3.5% without cirrus and 4.9% with cirrus, whereas the IPCC 1999 figure of 2% was more accurate, it believed. Professor David Lee, first author of the paper, called the criticism “confused and unhelpful”.
TIACA said it was disputing the increase published in a paper ‘Aviation and Global Climate Change in the 21st Century’ (see article), which includes updated values of kerosene fuel sales based on data reported by the International Energy Agency (IEA). The paper used the data to revise aviation’s radiative forcing (RF) to reflect an increase in traffic, fuel use and total aviation RF over the period 2000-2005, including estimates of cirrus cloud formation.
The industry association said it preferred to believe in a more accurate assessment reported in 1999 by the Intergovernmental Panel on Climate Change (IPCC), which estimated aviation emitted 2% of man-made CO2 and forecasted a rise to 3% in 2050. “The new report continues to confirm CO2 data that indicates aviation remains 2% of anthropogenic CO2 but the figure is then increased with the added impact of what TIACA calls ‘uncertain gases’,” says the TIACA statement.
Daniel Fernandez, TIACA’s Secretary General, said: “Aviation is the only industry that has asked the IPCC for a total assessment on climate change. The original assessment done in 1999 used RF as a way to assess the impact beyond CO2. Given the considerable uncertainty of the other gases, particularly those like aviation-induced cloudiness (AIC) that is unique to aviation, a more direct and understood comparison of aviation to other anthropogenic actives is better done via CO2.
“The air cargo industry takes its environmental responsibilities extremely seriously and has made significant advancements in reducing its carbon footprint. While we believe it is too early to count the impact of gases whose effect is not yet fully understood, TIACA will continue to monitor the effects of other gases – such as NOx, H2O vapour, contrails, AIC, sulphate particles and soot particles – have on climate change and as more is understood about what these effects are, we will be in a better position to correctly address how aviation can reduce its impact on the environment.”
Rebutting the criticism, Professor Lee, first author of the new paper and IPCC 1999/AR4 lead author commented: “It is a shame that TIACA has produced such a confused and unhelpful statement. All the points that they have referred to are very carefully explained in the paper and it is unfortunate that they have chosen not to read it properly.”
A joint statement issued by the authors of the paper said:
"TIACA has produced a very confused statement, which reflects their lack of understanding of the science quantification and data sources for assessing aviation’s impacts on climate. The original IPCC Fourth Assessment Report (AR4) estimation of various climate impacts (including aviation) was on a base year of 2005. The aviation data source reviewed by AR4 was for a base year of 2000, and it was not appreciated at the time of AR4 writing how much air traffic and emissions had increased over the period 2000 to 2005. Using data from IATA and the International Energy Agency, and the US Department of Energy’s Carbon Dioxide Information Analysis Center (CDIAC), we calculated an increased contribution of aviation to 2005 CO2 emissions and radiative effects.
“TIACA then goes on to state that a more accurate assessment was made in 1999 by the IPCC. Authors Lee, Fahey, Sausen and Forster were all involved in both the IPCC 1999 report, the IPCC Fourth Assessment Report and the paper in question. The scientific basis of aviation’s contribution to climate change has become more complete and less uncertain since the initial IPCC assessment some 10 years ago. Our new paper reflects these improvements in scientific understanding and the latest available information on global fuel use and global fleet operations.
“Our recent paper does not confirm that aviation is responsible for 2% of man-made CO2; it quantifies for the first time the rising proportion over time as an annual emission rate to a peak of 2.7% in 2001, declining to 2.5% in 2005. IEA statistics of fuel sales of kerosene are the most reliable available, which has long been known, since global inventories systematically underestimate emissions, and the UNFCCC/IPCC greenhouse gas reporting process is incomplete in coverage, so cannot be used for global aviation emissions estimates.”
Concerning the non-CO2 multiplier effect, Prof Lee told to GreenAir Online: “The multiplier concept can only be done one way: via a Global Warming Potential (GWP). Formulating the GWP is not the problem, it’s the input data from the detailed process models that is the problem.
“That there is an emissions multiplier, I have absolutely no doubt. The question is simply over its value, and at what time horizon – it will be relatively large at 5, 10, 20 years, and close to 1 at 80, 90, 100 years. Choice of time horizon is not a science choice, it is a science-informed policy choice.”
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