The authors that had assessed aviation's contribution to climate change to be 3% in the Fourth Assessment Reports (AR4) is now estimating aviation's contribution to climate change to be 3.5% without cirrus and 4.9% with cirrus.
The Intergovernmental Panel on Climate Change (IPCC) states in its 1999 report on aviation and climate change that airplanes emit 2% of man-made CO2 in 1992 and is expected to grow to 3% in 2050. The Aviation and Global Climate Change in the 21st Century report contains CO2 data that indicates aviation remains 2% of anthropogenic CO2.
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.
TIACA, however, will continue to monitor what effects other gases (NOx, H2O vapour, contrails, AIC, sulphate particles, and soot particles) have on climate change and as more is understood what these effects are, we will be in a better position to correctly address how aviation can reduce its impact on the environment.
The Intergovernmental Panel on Climate Change (IPCC) had updated aviation's contribution to climate change through its WGI and WGII in the Fourth Assessment Reports (AR4) published in 2007. The original report was done at the request of the aviation industry and was completed in 1999 based on 1992 data. AR4 assessed aviation's RF contribution for 2005 based upon an estimate of 2000 operations data. AR4 estimates that aviation contributes 3.0% to climate change.
The paper, Aviation and Global Climate Change in the 21st Century, revised AR4 value for aviation's contribution to climate change by updating values of kerosene fuel sales based on International Energy Agency reported data. This report used that 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. Aviation's percent of RF impact from the AR4 report of 3.0% is now estimated to be 3.5% without cirrus and 4.9% with cirrus.
The RF components from aviation includes CO2, NOx, H2O vapour, contrails, aviation-induced cloudiness (AIC), sulphate particles, and soot particles. Several of these gases have climate impacts (some cause cooling rather than warming). The paper notes that uncertainties for aviation RFs, other than that of CO2, are difficult to quantify. And that there are considerable uncertainties about the exact impacts and thus have wide error limits. The paper assigned the level of scientific understanding (LOSU) of:
* 'High' for CO2
* 'Medium-low' for O3 and CH4,
* 'Low' for H2O vapour, sulphate aerosol, soot aerosol and contrails
* 'Very low' for aviation-induced cirrus (AIC) cloud
Regardless, it is important to understand what these uncertainties might be, in order to assess the limitations of the RF estimates and to understand aviation's contribution to the environment within a wider policy framework.
This is one of several papers in the press summarizing the results of the European Commission ATTICA project which has been assessing the impact of the different transport sectors (road, aviation, and shipping) on climate. A summary of this report was submitted to ICAO's Group on International Aviation and Climate Change (GIACC) by the International Coalition of Sustainable Aviation, a group of international NGOs with observer status to UNFCCC and ICAO/CAEP. GIACC met in the last week of May and has sent their recommendations to the main ICAO body. We expect more reports like this to surface as the Copenhagen meetings approach at the end of the year.