, Volume 34, Issue 3-4, pp 405-437

Estimates of indirect global warming potentials for CH4, CO and NOX

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Abstract

Emissions may affect climate indirectly through chemical interactions in the atmosphere, but quantifications of such effects are difficult and uncertain due to incomplete knowledge and inadequate methods. A preliminary assessment of the climatic impact of changes in tropospheric O3 and CH4 in response to various emissions is given. For a 10% increase in the CH4 emissions the relative increase in concentration has been estimated to be 37% larger. The radiative forcing from enhanced levels of tropospheric O3 is estimated to 37% of the forcing from changes in CH4. Inclusion of indirect effects approximately doubles the climatic impact of CH4 emissions. Emissions of NOx increase tropospheric O3, while the levels of CH4 are reduced. For emissions of NOx from aircraft, the positive effects via O3 changes are significantly larger than the negative through changes in CH4. For NOx emitted from surface sources, the effects through changes in O3 and CH4 are estimated to be of similar magnitude and large uncertainty is connected to the sign of the net effect. Emissions of CO have positive indirect effects on climate through enhanced levels of tropospheric o3 and increased lifetime of CH4. These results form the basis for estimates of global warming potentials for sustained step increases in emissions.