Abstract
Reactive gas emissions (CO, NOx, VOC) have indirect radiative forcing effects through their influences on tropospheric ozone and on the lifetimes of methane and hydrogenated halocarbons. These effects are quantified here for the full set of emissions scenarios developed in the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios. In most of these no-climate-policy scenarios, anthropogenic reactive gas emissions increase substantially over the twenty-first century. For the implied increases in tropospheric ozone, the maximum forcing exceeds 1 W m−2 by 2100 (range −0.14 to +1.03 W m−2). The changes are moderated somewhat through compensating influences from NOx versus CO and VOC. Reactive gas forcing influences through methane and halocarbons are much smaller; 2100 ranges are −0.20 to +0.23 W m−2 for methane and −0.04 to +0.07 W m−2 for the halocarbons. Future climate change might be reduced through policies limiting reactive gas emissions, but the potential for explicitly climate-motivated reductions depends critically on the extent of reductions that are likely to arise through air quality considerations and on the assumed baseline scenario.
Highlights
Anthropogenic emissions of the reactive gases, carbon monoxide (CO), nitrogen oxides (NOx ϭ NO ϩ NO2, emitted mainly as NO) and nonmethane volatile organic compounds (VOC; a group including ethane, acetylene, propane, propene, toluene, etc.) affect the reactive chemistry of the earth’s atmosphere, and so influence the rates of production and decay of many other species
The purpose of this paper is to describe and quantify the radiative forcing effects of these reactive gases for the full range of scenarios from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES; Nakicenovicand Swart 2000)
Given the substantial uncertainty in the more complex model results and the limits on the number of assessment scenarios that could be computed with 3D models, the results may be justifiably represented by simple linear relationships relating greenhouse gas lifetimes and tropospheric ozone increment to reactive gas emissions
Summary
The purpose of this paper is to describe and quantify the radiative forcing effects of these reactive gases for the full range of scenarios from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES; Nakicenovicand Swart 2000). As derived by the IPCC, these relationships were calibrated over a range of changes from the current atmosphere to the largest SRES emissions. They enable evaluation of the implications of a variety of emissions scenarios in a consistent framework, as is done in this paper
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