Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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6.1.4. Aviation's Contribution to the CO 2 Budget
Carbon dioxide released from fossil fuel combustion rapidly equilibrates among atmosphere,
surface ocean, and parts of the biosphere, leaving behind excess atmospheric CO 2 that
decays slowly over the following century (see carbon cycle discussion in IPCC, 1996). Thus,
for CO 2 radiative forcing, it makes no difference whether the fossil fuel is burned in aircraft
or other transportation/energy sectors, and the relative role of aircraft can be found by
comparing the history of fuel burned by aviation with that of total anthropogenic carbon
emissions.
Comparing projected IS92a carbon emissions from fossil fuels in Figure 6-6, CO2 emissions
from aircraft in 1990 account for about 2.4% of the total; they are projected to grow to about
3% (Fa1) or more than 7% (Eab) of all fossil fuel carbon emissions by 2050. Sustained
growth in air traffic demand (5%/yr compounded) envisaged in Edh would lead to an
aviation fraction of more than 10% by 2050. By comparison, the entire transportation sector
is currently about 25% of the total (see discussion in Chapter 8). Clearly, different economic
projections, as well as uncertainties in predicting demand for air travel and aviation's ability
to meet that demand, can alter this aviation fraction by more than a factor of 2. Technology
option 2 (low-NOx engines, Fa2) increases this fuel fraction slightly to 3.2%, and the HSCT
option increases this fraction from 3.1% (Fa1) to 3.6% (scenario Fa1H, assuming no change
in air traffic demand) by the year 2050.
The cumulative history of CO2 emissions allows us to calculate the excess atmospheric
CO2 concentration attributable to aircraft, as shown in Figure 6-8. These calculations are
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Figure 6-8: Atmospheric CO 2 (ppmv) accumulated from aviation's
use of fossil fuel beginning in 1940.