Abstract
Abstract. We examine the air quality (AQ) and radiative forcing (RF) response to emissions reductions by economic sector for North America and developing Asia in the CAM and GISS composition/climate models. Decreases in annual average surface particulate are relatively robust, with intermodel variations in magnitude typically <30% and very similar spatial structure. Surface ozone responses are small and highly model dependent. The largest net RF results from reductions in emissions from the North America industrial/power and developing Asia domestic fuel burning sectors. Sulfate reductions dominate the first case, for which intermodel variations in the sulfate (or total) aerosol optical depth (AOD) responses are ~30% and the modeled spatial patterns of the AOD reductions are highly correlated (R=0.9). Decreases in BC dominate the developing Asia domestic fuel burning case, and show substantially greater model-to-model differences. Intermodel variations in tropospheric ozone burden changes are also large, though aerosol changes dominate those cases with substantial net climate forcing. The results indicate that across-the-board emissions reductions in domestic fuel burning in developing Asia and in surface transportation in North America are likely to offer the greatest potential for substantial, simultaneous improvement in local air quality and near-term mitigation of global climate change via short-lived species. Conversely, reductions in industrial/power emissions have the potential to accelerate near-term warming, though they would improve AQ and have a long-term cooling effect on climate. These broad conclusions appear robust to intermodel differences.
Highlights
Changes in air quality (AQ) and climate typically occur on different temporal and spatial scales
As climate change is by definition a long-term phenomenon, climate policy typically focuses on well-mixed greenhouse gases, as these have strong radiative forcing and are long-lived in the atmosphere
Though forcings were calculated for the Goddard Institute for Space Studies (GISS) model only, we have shown that values for radiative forcing (RF) from sulfate are likely to be fairly consistent in the two models given the similarity in modeled aerosol optical depth (AOD) changes, indicating that the response to industrial/power sector perturbations is relatively robust
Summary
Changes in AQ and climate typically occur on different temporal and spatial scales. As climate change is by definition a long-term phenomenon, climate policy typically focuses on well-mixed greenhouse gases, as these have strong radiative forcing and are long-lived (residence times of ∼10 years or longer) in the atmosphere. We concentrate here on the near-term forcing over the two decades from potential present-day emissions perturbations This timescale is chosen to be long enough that the climate system would have sufficient time to respond to a substantial portion of the forcing from short-lived species, which occurs virtually right away following emissions changes, but not to be so long that AQ-related emissions would likely diverge enormously from their current levels Since we consider acrossthe-board reductions in emissions from a given sector, our results are useful for assessing the potential impacts of reductions in total power/fuel usage rather than changes in the mix of power generation/transportation types or in emissions control technologies targeted at specific pollutants We examine both the net forcing from each sector and the contribution from individual species, so that both the sectors and individual pollutants within sectors that are the most attractive climate mitigation targets can be determined. This work complements prior regional and sectoral perturbations studies examining the response of gas-phase species only (Berntsen et al, 2005; Fuglestvedt et al, 1999; Derwent et al, 2001), aerosol species only (Koch et al, 2007), or both but with a subset of the species included here (Unger et al, 2008) or for a single sector for the entire globe (Fuglestvedt et al, 2008)
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