The category transport/plane/generic contains data on CO2 emissions associated with 'typical' forms of air travel, sourced from the UK government agency DEFRA/DECC.
This dataset follows the CORINAIR guidebook data and methodology but emissions are calculated on a per passenger basis, assuming typical aircraft types and load factors.
Domestic and short-haul flight emissions calculations are based on fuel consumption data for the Boeing 737 aircraft and a typical passenger loading at 65% of capacity. Long-haul flight emissions reflect the fuel consumption of Boeing 747 aircraft and a passenger loading of 79.7%. These scenarios incorporate the fuel consumption associated with both the landing-take off cycle and cruising, and therefore reflect the respective typical portions of short- and long-haul flights which is represented by cruising.
Per passenger CO2 emissions for a given flight depend on the flight distance and passenger class, both of which can be specified by the user. Additionally, users can choose to incorporate a Radiative Forcing Index (RFI) factor to account for the global warming effects of non-CO2 emissions.
Users can set flight distance in one of three ways: (1) directly, by specifying an actual distance flown; (2) indirectly, by specifying departure and destination locations; or (3) approximately, by using generic distance categories.
Specifying departure and destination locations
Users can enter either the latitude/longitude of the departure and destination locations or IATA codes for the respective airports involved in travel. In both cases, CarbonKit calculates the distance based on a 'great-circle' calculation (using the haversine formula), and inflates by 9% to account for congestion and indirect routing.
To use this method, select the auto category via drill down, and select from either one-way or return. If a return flight is chosen, emissions are simple double the one-way calculation. Next, enter departure and destination locations by setting one of the following groups of profile item values:
- lat1, long1, lat2, long2 (i.e. a pair of latitude and longitude coordinates)
- IATACode1, IATACode2 (i.e. a pair of airport IATA codes)
If no IATA codes are specified but long1 is set to a valid value then the great circle distance is calculated directly between long1, lat1 and long2, lat2 (and inflated by 9%). Longitude must be in the range -180 to 180 with negative numbers representing eastern longitudes. Latitudes must be in the range -90 to 90 with negative numbers representing southern latitudes.
Depending on the distance calculated, CarbonKit selects the appropriate CO2 emissions factor(kg CO2 per passenger km). A short haul emissions factor is used for flights under 3700 km, while a long haul factor is used for those greater than 3700 km. For flights originating and landing within a single country, the domestic emissions factor is used. Users can additionally specify the number of passengers and the number of flights being accounted for using the numberOfPassengers and journeys profile item values (both defaulting to 1). The value returned is the kg CO2 emitted by all passenger journeys, calculated as follows:
kg CO2total = kg CO2per passenger km * (distance * 1.09) * number of passengers * number of journeys
Note: the distance profile item value is ignored in this method.
Directly specifying a distance
Users can alternatively specify the total distance flown. To use this method, specify the type of flight by selecting domestic, short haul, or long haul via drill down, followed by "-" for the flight size. Next, set the distance flown per year in the distance profile item value. CarbonKit calculates emissions by using the appropriate domestic, short-haul or long-haul emissions factor (kg CO2 per passenger km). Users may also specify the number of passengers under consideration by setting the numberOfPassengers profile item value (default = 1). The returned value represents annual CO2 emissions for all passengers, calculated as follows:
kg CO2annual = kg CO2per passenger km * distanceannual * number of passengers
Note: the journeys profile item value is ignored in this method - emissions are based on the total distance flown in one year.
Generic distance categories
If flight distances, or specific journey departure and destination locations are not available, users can calculate flight emissions based on 'typical' distance categories. There is no widely accepted definition of the terms "domestic", "short haul" and "long haul", though CarbonKit follows DEFRA/DECC in assuming the following typical one way flight distances:
- domestic = 463 km
- short-haul = 1108 km
- long-haul = 6482 km
Per passenger journey CO2 emissions factors are calculated as follows: kg CO2per passenger journey = kg CO2per passenger km * typical journey distance
Total CO2 emissions are then calculated according to: kg CO2total = kg CO2per passenger journey * number of passengers * number of journeys
To use this method, specify the type of flight by selecting domestic, short haul, or long haul via drill down, followed by one way or return for the flight size. If a return flight is chosen, emissions are simple double the one-way calculation. Next, set the number of journeys in the journey profile item value, and the number of passengers by setting the numberOfPassengers profile item value. If left unspecified, both of the profile item values default to 1. Returned values represent CO2 emissions for all passenger journeys.
Users can also specify the passenger class used, from which CarbonKit will attempt to look up a more precise per passenger emission factor from the category /transport/plane/generic/passengerclass. The passengerClass profile item value can be populated by the following valid values:
- economy plus
Radiative Forcing Index
Uncertainty over the environmental impact of aircraft emissions arises from the complexity of atmospheric chemistry, particularly in relation to the emission of non-CO2 products (e.g. water vapour, contrails, NOx) at high altitudes, which is argued to exert a greater global warming effect compared with similar emissions at ground level. These effects can be accounted for by using a multiplicative factor called the Radiative Forcing Index (RFI), which represents the ratio of all radiative forcing (CO2 + non-CO2 emissions) to that arising from CO2 emissions only. Estimates for RFI range between 1 and 4 with a value of 2.7 recommended by the IPCC in 1999. No specific recommended value was quoted in the most recent IPCC report (2007), and the current best estimate for RFI is 1.9 (Sausen et al. (2005)). Following the DEFRA/DECC methodology (e.g. as used in Act_On_CO2) for flight-based emissions, CarbonKit returns values for CO2 emissions only - i.e. with no RFI applied. Users can elect to incorporate the RFI by setting the useRFI profile item value to "true", and entering a value for RFI in the radiativeForcingIndex profile item value. If no value is entered in the radiativeForcingIndex profile item value, a default factor of 1.9 will be applied.
Alternatively, user can specify their own emissions factors by using the user defined plane emissions category.
Further information can be found in the flight section of the DEFRA methodology paper.