business class, which represents only about 8.5 percent of global passenger kilometers, the WBG share is more than 8 times as high.

# **5.3 Total Footprint Calculation for HQ-Booked WBG Air Travel in CY-09**

Our final step is to derive the overall carbon footprint of HQ-based WBG air travel for CY-09. Note that ICAO‘s method for calculating the footprint relies on (a) obtaining fuel consumption figures of the aircraft involved, (b) making adjustments for the overall distance traveled in the flight, (c) multiplying the fuel burnt by a factor of 3.157 (which is the number of tons of CO2 released when burning one ton of jet fuel), (d) applying the appropriate load factors (see table 5 above), and (e) assigning the seat portion of this footprint. Our calculated fuel consumption is based on 48 known and specified aircraft types. Other aircraft types, that have similar consumption patterns to specific known aircraft types, are assigned a related “equivalency” code, yielding a total set of 196 aircraft types to be included.<sup>26</sup> This means, for example, that a 737-300 or 737-500 will be treated identically to a 737-400. Trips are also placed in 16 distance classes ranging from 125 nautical miles to over 6,000 nautical miles, with (as noted above) consumption per distance reduced by trip length up to a limit, and increased beyond that limit.

The formula for computing the average carbon footprint related to air travel is then: CO2 per pax = 3.157 * (total fuel*pax-to-freight factor)/(number of y-seats*pax load factor).

In ICAO’s emissions calculator, a multiplier of 2 is added at the end of the calculation for passengers in premium classes. In our calculations, the proportion of a class’s contribution to the footprint was established earlier, and is also adjusted proportionally to the overall (and in Phase III, class-specific) load factor. The important distinction is that in simply using a class multiplier as in the current ICAO methodology, the calculation ignores the shift in load factors from one class to another, which alters each class’s overall multiplier. In addition, though ICAO’s average multiplier of 2 appears to be not very biased on the average, first class passengers should have a multiplier of around 4.5 or higher.

Applying a hybrid of the ICAO calculation combined with the parameters of the three phases, calculations for overall footprints for HQ-based travel were calculated, and presented in Table 5.2. Since we as noted have no definitive data available on load factors by class, we need to make assumptions about these in Table 5.2. The table shows how different combinations of average load factors in first and business class, with the known overall regional load factor applied in step 2, affect the overall footprint. For obvious reasons, the highest impact depends heavily on average load factors in premium classes; both business class (due to the large share of flights in this class), and first class (due to the high footprint per mile on that class). For a business class load factor of 0.6 and a first class load factor of 0.4 (which are reasonable

> 26 ICAO bases this methodology on the European Environment Agency’s EMEP/CORINAIR Emission Inventory Guidebook of 2006.

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