GREENHOUSE GAS EMISSION BASELINES ■ 33and take-off cycle are allocated to the area in which the airport is based (this
is the same approach as is adopted in air quality emissions), and the emissions
associated with the cruise phase are allocated to the region in which the pas-
senger resides. More complicated issues concerning tourists, transferring pas-
sengers, and freight are also discussed next.
Waste
Th e determination of GHG emissions associated with waste is where the greatest
discrepancies in methodology are apparent. In particular, emissions from the land
fi lling of solid waste have been calculated using at least three diff erent techniques
(table 2.2): (1) scaling from national inventories, (2) a total yields gas approach, and
(3) the U.S. Environmental Protection Agency’s (EPA’s) Waste Reduction Model
(WARM). Two further techniques could also have been used: (4) measurement
from waste in place and (5) local application of IPCC’s fi rst-order decay approach.
Th e divergence of approaches for determining emissions from waste is per-
haps partly due to the complexity of emissions from landfi lls. Th e biodegrada-
tion of solid waste to form methane and other landfi ll gases occurs over time
scales extending beyond a single year. Hence, researchers fi nd it challenging to
assign GHG emissions from waste to a particular year.
Th e IPCC’s recommended approach (5) involves calculation of emissions
in the inventory year, based on historical waste deposited over previous years.
An alternative (4) would be to actually monitor and measure emissions in the
inventory year, but this requires considerable monitoring and may be challeng-
ing for commercial and industrial waste streams if they are managed by the
private sector.
Scaling solid waste emissions from national inventories (1) should give
results that approximate those from approaches 4 and 5. Such scaling has been
used in the GRIP studies (using its aforementioned level 2 and 3 methods; Car-
ney and others 2009).
Th e total yields gas approach (2) was formerly recommended by the IPCC
(1997). Essentially it takes the total amount of waste produced by an urban
area in a given year and then determines the total emissions released from this
waste, regardless of how many years transpire before the full release occurs.
Th is approach has been used by Dubeux and La Rovere (2007) and Kennedy
and others (2009, 2010).
Th e EPA’s WARM model (3) uses a life-cycle accounting approach, which
is ideal in some respects but not in others. Th e model recognizes, for exam-
ple, that the recycling of waste reduces emissions from the harvesting of raw
materials; hence a credit can be applied. Th e problem is that emissions asso-
ciated with material fl ows of paper and plastics into cities are not currently