GREENHOUSE GAS INVENTORY FOR 2008
The UN Greenhouse Gas Calculator methodology is ex- plained in detail in its user manual1
. The calculator and
the user guide provide step-by-step instructions on how to prepare an inventory according to the common boundary agreed by the UN system for its GHG account- ing. After the required activity data are entered into the tool, the GHG footprint is automatically estimated by applying a set of default emission factors, allowing flex- ibility to enter more specific data where available.
International Civil Aviation Organization (ICAO) Aviation Carbon Emissions Calcu- lator The International Civil Aviation Organization (ICAO), one of the UN system organizations, has developed a methodology for calculating the carbon dioxide emis- sions from official air travel. A tool for calculating emis- sions is available on the ICAO website together with a description of the methodology underpinning the Cal- culator. The UN system organizations have chosen to use this tool for estimating emissions from air travel as there can be very significant differences in emissions for the same trip travelled via different routings2
. A spe-
cial interface to the ICAO tool was developed by the ICAO secretariat for specific use by the UN system or- ganizations, to facilitate the aggregation of travel data. This tool complements the UN Greenhouse Gas Calcu- lator. The methodology applies the best publicly avail- able industry data to account for various factors such as aircraft types, route specific data, passenger load factors and cargo carried. The methodology makes a distinction between cabin class factors “economy” and “premium”, and weights these with a ratio of 1:2.
Non-CO2 emissions from air travel
The full climate impact of air travel goes beyond the effect of CO2
emissions alone. For example, aircraft
emit nitrogen oxides (NOx) which tend to increase the level of ozone and reduce the level of methane, both of which are greenhouse gases. Aircraft also contribute to water condensation in the atmosphere which has a warming effect. There is still considerable scientific un- certainty about the scale and dynamics of these effects.
The “Special Report on Aviation and the Global Atmo- sphere”, prepared by the Intergovernmental Panel on Climate Change (IPCC) in 1999, estimated the overall climate impact of aviation to be between two to four times larger than that of the CO2
The decision to account provisionally only for CO2 emis-
sions has resulted in some UN organizations describing their current approach as carbon neutral (as opposed to climate neutral), but the goal of reaching climate neutrality remains in place.
emissions alone. It
used a Radiative Forcing Index (RFI) in these estimates. The RFI for aircraft in 1992 was estimated to be 2.7 with
2. The World Bank Group continues to use the WRI/WBCSD metho dology with the latest DEFRA emission factors to calculate its emissions from business travel.
Alternative reporting format An alternative reporting format was made available to UN agencies which had already concluded their GHG inventory for 2008 before the inventory tools were avail- able or where other means of compiling the inventory had been used. If methods other than that agreed by the WRI/WBCSD were used, the assumptions had to be explained in the individual organization’s inventory management plan. Information on emissions for each of the Kyoto Protocol gases, kilometres travelled, number of trips and kWh electricity used etc. was to be entered in this pre-formatted Excel spreadsheet. Data submitted in this alternative format was treated in the same way as data submitted in the UN GHG Calculator inventory tool.
aviation’s total contribution to radiative forcing being approximately 3.5 per cent.
More recent data in the 2007 IPCC “Fourth Assessment Report” suggests an RFI of 1.9 for aircraft in 2005 and aviation’s contribution being at 3 per cent. Although ref- erence to the RFI is made, the report states that the RFI should not be used as an emission metric since it does not account for the different residence times of different forcing agents. Other metrics such as Global Warming Potential (GWP) and Global Temperature Potential (GTP) could be considered as alternatives. However, to date, the IPCC has not provided further guidance on these issues, but work is underway in the Fifth Assessment Report.
In its decision on how to consider the effect of non- CO2 gases, in the EMG, the UN system organizations weighed up various factors, including scientific uncertainty, risk to reputation, the need to follow the precautionary approach, the need to maintain high environmental standards, and legal and budgetary considerations. A collective decision was taken, on a provisional basis and until further guidance is provided by the IPCC, in keep- ing with the current WRI/WBCSD methodology, only to take into account the effects of CO2
from air travel.
The ICAO and UNEP secretariats were also requested to convene a meeting of experts who will be identified based on, inter alia, recommendations of the IPCC. The meeting will aim to provide further guidance as a mat- ter of priority on the question of an appropriate metric to account for all GHG effects from aviation, while wait- ing for additional guidance from the IPCC. Preparations are underway to convene this meeting in spring 2010.
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