A44A-01 INVITED
Extreme Global Warming and Local Cooling Due to Aerosol Particles
Fossil-fuel soot (FFS) aerosol particles are known to warm climate above the warming due to anthropogenic greenhouse gases (AGHG). Other anthropogenic aerosol particles (AAP) are also known to mask much of global warming. However, to date, no climate response study has treated the physical evolution of the mixing state of FFS from hydrophobic to hygroscopic or tracked FFS and other AAP through clouds and precipitation. Such a calculation reveals less cloud activation by newly-emitted FFS than other AAP, with increasing activation over time, consistent with data. Both strong atmospheric heating and reduced cloud activation by FFS causes it to enhance extreme global warming more than previously thought. All previous studies have also ignored the majority of chemicals in AAP, underestimating cooling. As such, previous studies of the historic climate record that have matched the temperature data have done so with offsetting errors. Since extreme global warming and localized cooling observed in the climate record are due to anthropogenic aerosol particles, control of FFS will reduce extreme warming.
A44A-02 INVITED
Ozone Air Quality and Radiative Forcing Consequences of Changes in Ozone Precursor Emissions
Changes in emissions of ozone (O3) precursors affect both air quality and climate. We first examine the sensitivity of surface O3 concentrations (O3srf) and net radiative forcing of climate (RFnet) to reductions in emissions of four precursors - nitrogen oxides (NOx), non-methane volatile organic compounds, carbon monoxide, and methane (CH4). We show that long-term CH4-induced changes in O3, known to be important for climate, are also relevant for air quality; for example, NOx reductions increase CH4, causing a long-term O3 increase that partially counteracts the direct O3 decrease. Second, we assess the radiative forcing resulting from actions to improve O3 air quality by calculating the ratio of ΔRFnet to changes in metrics of O3srf. Decreases in CH4 emissions cause the greatest RFnet decrease per unit reduction in O3srf, while NOx reductions increase RFnet. Of the available means to improve O3 air quality, therefore, CH4 abatement best reduces climate forcing.
A44A-03 INVITED
Linking Aerosol Source Activities to Present and Future Climate Effects
Aerosol source sectors (transport, power, industry, residential, biomass burning) generate distinct mixtures of aerosol species. These mixtures in turn have different effects on climate. As sectoral emissions change in coming decades, whether by regulation or not, it is helpful to link pollution from source types to climate consequences. We do so, using our global (GISS GCM) aerosol model for present and future IPCC SRES scenarios. According to our model, residential and transport sectors have net positive 1995 aerosol forcings (0.04 and 0.03 W m-2) due to their large black carbon contents. However, the sulfate-dominated power and industry sectors have net negative 1995 forcings (-0.10 and -0.09 W m-2). Due to the near-balance of absorbing and scattering components, biomass burning forcing is small. For the 2050 SRES A1B scenario, the net (negative) aerosol forcing is double 1995 due primarily to increased sulfur emissions in the industry and power sectors. For 2050 B1 the net (negative) forcing decreases relative to 1995, as sulfur emissions are reduced. Both future scenarios project decreasing residential emissions. Yet transport emissions are expected to remain significant and thus become the dominant source of warming aerosols in the future. Aerosol pollution is projected to shift southward relative to the present, as the current industrialized regions generally reduce emissions and tropical and southern hemispheric regions continue to develop. Similar to these SRES scenarios, IIASA scenarios project a decline in residential emissions; however IIASA is more optimistic about transport sector emissions reductions. We will conduct present-day climate experiments, including aerosol direct and indirect effects, to study impacts of power and transport sectors on climate features such as air temperature and hydrologic cycle.
A44A-04
GCM evaluation of the synergy of future air pollution and climate mitigation strategies: a sectorial analysis of GHG and aerosol impacts
Future climate change and air pollution mitigation strategies will both alter the emissions and concentrations of a range of climate relevant gases which act as forcing agents in the Earth System. Mitigation policies focusing on climate change or air pollution are in many cases not linked to each other, despite the fact that greenhouse gases, chemical active gases and aerosols have common sources. In addition, climate forcings do not act independently in the Earth System, but are often highly non-linearly coupled. Aerosol forcings, for example, are non-linearly coupled through microphysical aging processes and aerosol and greenhouse gas forcings are linked through the hydrological cycle. However, most of the model studies so far assessed climate impacts of specific forcing agents independent of each other. We aim for a integrated approach, assessing the combined climate effect of greenhouse gases, chemically active gases and aerosols. Thereby, we focus on specific economic source sectors to explore the combined impacts of climate protection and air pollution strategies. Experiments are performed with a global atmospheric general circulation model (ECHAM5) extended by a microphysical aerosol model (HAM). This model enables us to account for both the direct and indirect aerosol effects. We analyze the impact of a number of established emission scenarios for specific economic sectors and different abatement strategies (current legislation and maximum feasible reduction) for the year 2030. In a first step, we estimated the aerosol radiative forcing of these established emission scenarios under present day conditions. The aerosol radiative forcing (top of the atmosphere, whole sky) for the year 2030 compared to present-day conditions (2000) range between -0.17 W/m2 for the current legislation abatement strategy and + 1.12 W/m2 for the maximum feasible reduction scenario. For comparison, the total present day anthropogenic aerosol effect (present day minus pre-industrial) is simulated as -1.95 W/m2 within the ECHAM5-HAM model. For a subset of these emissions scenarios we perform climate equilibrium experiments to investigate the combined effects of greenhouse gas and aerosol emission mitigation strategies in the Earth System.
A44A-05
Nonlinear Source -" Receptor Relationship due to Interactions between Atmospheric Constituents, Water Cycle and Biogenic Emissions
Specific economic sectors or source regions emit a wide variety of air pollutants which influence climate and air quality. This includes emissions of greenhouse gases, chemical species which affect the oxidation capacity of the atmosphere and the concentrations of ozone and methane, and aerosol particles or aerosol precursors. Regional climate respectively weather controls transport and removal of pollutants, chemical transformation pathways, particle formation rate and sink processes as well as emissions from natural sources. Interactions between aerosols and trace gases modify their global and regional distributions. Thus, climatic and environmental impacts are not only controlled by amount and chemical composition of pollutant emissions but in addition also by their interactions and the local meteorological conditions in the source region. For the development of mitigation strategies to minimize adverse conditions attributed to climate change and air pollution we need a better understanding of the role of source location, impact of interactions and feedbacks and of the influence of climate change on the chemical composition of the atmosphere. To demonstrate interactions and feedbacks between the cycles of gaseous and particulate atmospheric constituents, the water cycle, the biosphere and the changing climate we will present results of a series of numerical model simulations. Investigations include interactions between greenhouse gas warming, water cycle and aerosol cycle (Feichter et al., 2004), between aerosol cycles (Stier et al., 2006), between marine biogeochemistry and aerosol cycles (Kloster et al., 2006), and between gas-phase air chemistry and aerosol constituents (Pozzoli et al., 2007). The presentation discusses possible interactions and feedbacks and emphasizes the need for a better integration of the different Earth system components in climate and air quality models. Finally, the question whether anthropogenic emissions from different regions result in different climate sensitivity will be raised. Feichter J, Roeckner E, Lohmann U., Liepert B (2004): Nonlinear aspects of the climate response to greenhouse gas and aerosol forcing, Journal of Climate; 17, No 12, 2384-2398. Kloster, S. , Feichter, J., Maier-Reimer, E., Roeckner, Wetzel, P., Six, K.D., Stier, P. and Esch, M., (2007): Response of dimethylsulfide (DMS) in the ocean and atmosphere to global warming, J. Geophys. Res. (subm). Stier, P., J. Feichter, S. Kloster, E. Vignati, and J. Wilson (2006): Emission-Induced Nonlinearities in the Global Aerosol System - Results from the ECHAM5-HAM Aerosol-Climate Model, J. Clim Pozzoli L, I Bey, S Rast, M Schultz, P Stier and Feichter, (2007): Trace gas and aerosol interactions in a global coupled model of chemistry-aerosol-climate (to be subm.).
A44A-06
In-field Greenhouse Gas Emission Factors from Residential Cook Stoves in Michoacé¡n, Mexico
A44A-07
What is the influence from biomass burning and/or climate change on changing ozone in the western US?
In a recent study (Jaffe and Ray, 2007), we identified a broad and statistically significant pattern of increasing daytime O3 at 7 of 9 rural sites in the western U.S. These sites show an average O3 increase of 0.3 ppbv/year in O3 over the past ~18 years. Surprisingly, this increase is present in all seasons. In this study we explore whether climate change (changes in temperature) and/or increasing biomass burning play a role in changing ozone across the this region. To do this we examined variations in O3 and PM2.5 at numerous rural sites in the western U.S. that are part of the IMPROVE and/or CASTNET monitoring programs. Using a fire database that was developed from state and federal fire reports (Westerling et al., 2006), we find good correlations between area burned and PM2.5 and O3 concentrations at most sites. In some cases, we also found a correlation between air quality in one region and area burned another region, indicating transport of smoke and other emissions from the fires. During large fire years, summertime mean PM2.5 and O3 are enhanced by 4-5 ug/m3 and 6-7 ppbv, respectively. There is also a significant correlation between fires and temperature. Thus a changing fire regime may be responsible for increasing O3 in the western US during summer and can have a significant influence on our ability to meet air quality objectives.