Estimates of the Climate Response to Aircraft CO2 and NOx-Emission Scenarios

Kurzfassung

A combination of linear response models is used to estimate the transient changes in the global means of carbon dioxide (CO₂) concentration, surface temperature, and sea level due to aviation. Apart from CO₂, the forcing caused by ozone (O₃) changes due to nitrogen oxide (NO_x) emissions from aircraft is also considered. The model is applied to aviation using several CO2 emissions scenarios, based on reported fuel consumption in the past and scenarios for the future, and corresponding NO_x emissions. Aviation CO₂ emissions from the past until 1995 enlarged the atmospheric CO₂ concentration by 1.4 ppmv (1.7% of the anthropogenic CO₂ increase since 1800). By 1995, the global mean surface temperature had increased by about 0.004 K, and the sea level had risen by 0.045 cm. In one scenario (Fa1), which assumes a threefold increase in aviation fuel consumption until 2050 and an annual increase rate of 1% thereafter until 2100, the model predicts a CO₂ concentration change of 13 ppmv by 2100, causing temperature increases of 0.01, 0.025, 0.05 K and sea level increases of 0.1, 0.3, and 0.5 cm in the years 2015, 2050, and 2100, respectively. For other recently published scenarios, the results range from 5 to 17 ppmv for CO₂ concentration increase in the year 2050, and 0.02 to 0.05 K for temperature increase. Under the assumption that present-day aircraft-induced O₃ changes cause an equilibrium surface warming of 0.05 K, the transient responses amount to 0.03 K in surface temperature for scenario Fa1 in 1995. The radiative forcing due to an aircraft-induced O₃ increase causes a larger temperature change than aircraft CO₂ forcing. Also, climate reacts more promptly to changes in O₃ than to changes in CO₂ emissions from aviation. Finally, even under the assumption of a rather small equilibrium temperature change from aircraft-induced O₃ (0.01 K for the 1992 NO_x emissions), a proposed new combustor technology which reduces specific NO_x emissions will cause a smaller temperature change during the next century than the standard technology does, despite a slightly enhanced fuel consumption. Regional effects are not considered here, but may be larger than the global mean responses.