REPORTS - SPECIAL REPORTS

Aviation and the Global Atmosphere


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6.3.2. Radiative Forcing for CO2

Carbon dioxide has a long atmospheric residence time (on the order of many decades); hence, aircraft CO2 becomes well mixed within the atmosphere and can be treated together with other anthropogenic CO2 emissions in conventional global warming simulations (e.g., Washington and Meehl, 1989; Cubasch et al., 1992; Murphy and Mitchell, 1995). The aircraft influence depends on the temporal evolution of the amount of the CO2 increase that can be attributed to aircraft emissions, which is directly proportional to the amount of fuel burned. See Section 6.1.2 and Table 6-2 for the calculation of CO2 increases attributed to aviation.

Over the period 1990 to 2050, under IS92a we expect an increase in atmospheric CO2 of about 155 ppmv from burning of fossil fuels, cement production, and other anthropogenic activities that release biospheric carbon. By 2050, F-type aviation scenarios produce a 5-7 ppmv increase, and the high-growth Edh scenario leads to a 13 ppmv increase. Thus, aviation in these scenarios would be responsible for 3-8% of the total anthropogenic increase in CO2 from 1990 to 2050.

The RF for aviation CO2 in 1992 is estimated to be +0.018 W m-2, with a likely range of 30% that includes uncertainties in the carbon cycle and in radiative calculations (see WMO, 1999). Uncertainties and confidence intervals discussed here do not include possible errors in predicting future scenarios. By 2050, the different aviation scenarios have a range of +0.06 to +0.16 W m-2. The technology option 2 scenario (Fa2) leads to a 0.1 ppmv increase in CO2 by 2050, with only a small increase in CO2-RF.

The HSCT option, F1aH, has 18% greater fuel use but only 8% greater CO2 concentrations by 2050, with a corresponding increase in CO2-RF from +0.074 to +0.080 W m-2. Because the HSCT fleet has just reached maturity in 2040, the extra fuel consumption of the HSCT aircraft is barely felt in terms of the accumulation of CO2. Similarly, the CO2 impact of new subsonic technologies that are introduced linearly between 2015 and 2050 is not fully effected by 2050. A fuller evaluation would have to extend the assessment beyond 2050, when the cumulative effects of mature fleets would be felt (e.g., Sausen and Schumann, 1999).


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