Aerosol climate effects and air quality impacts from 1980 to 2030

Abstract

We investigate aerosol effects on climate for 1980, 1995 (meant to reflect present day) and 2030 using the NASA Goddard Institute for Space Studies climate model coupled to an on-line aerosol source and transport model with interactive oxidant and aerosol chemistry. Aerosols simulated include sulfates, organic matter (OM), black carbon (BC), sea-salt and dust and, additionally, the amount of tropospheric ozone is calculated, allowing us to estimate both changes to air quality and climate for different time periods and emission amounts. We include both the direct aerosol effect and indirect aerosol effects for liquid-phase clouds. Future changes for the 2030 A1B scenario are examined, focusing on the Arctic and Asia, since changes are pronounced in these regions. Our results for the different time periods include both emission changes and physical climate changes. We find that the aerosol indirect effect (AIE) has a large impact on photochemical processing, decreasing ozone amount and ozone forcing, especially for the future . Ozone forcings increase from 0 to 0.12 W m −2 and the total aerosol forcing decreases from −0.10 to −0.94 W m −2 (AIE decreases from −0.13 to −0.68 W m −2 ) for 1995-1980 versus 2030-1995. Over the Arctic we find that compared to ozone and the direct aerosol effect, the AIE contributes the most to net radiative flux changes. The AIE, calculated for 1995-1980, is positive (1.0 W m −2 ), but the magnitude decreases (−0.3 W m −2 ) considerably for the future scenario. Over Asia, we evaluate the role of biofuel-and transportation-based emissions (for BC and OM) via a scenario (2030A) that includes a projected increase (factor of 2) in biofuel-and transport-based emissions for 2030 A1B over Asia. Projected changes from present day due to the 2030A emissions versus 2030 A1B are a factor of 4 decrease in summertime precipitation in Asia. Our results are sensitive to emissions used. Uncertainty in present-day emissions suggests that future climate projections warrant particular scrutiny.

Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

“…We estimate the AIE by taking the difference in net cloud radiative forcing between time periods (Figure 2) for the simulations with ACI and the simulations without. The past AIE is −2.0 Wm −2 , higher than previous GISS model estimates (Menon et al, 2008a;Koch et al, 2009) and estimates based on constraints from the temperature record using a parameterized AIE treatment in a similar version of the GISS model (Hansen et al, 2005). However, changes in CDNC in the Koch et al (2009) simulations are about half of that obtained in this study since the Koch et al study used a different set of emissions that had a lower sulfate burden change.…”

“…Over land locations, coincident retrievals of aerosols and cloud properties are not easily available from satellites and thus evaluation of changes to cloud properties from aerosols is more difficult. Over some land locations such as the Arctic, model-simulated values of the CDNC have been found to be too large, compared to satellite-retrievals, though COD and effective radii were within the observed range (Menon et al 2008a). A more meaningful global evaluation of the AIE is challenging in the absence of global observations of CDNC that serve as the main link between aerosols and cloud properties.…”

“…To our knowledge, the impact of aerosols on tropospheric chemistry through their modification on clouds remains poorly quantified. A recent model study found that the aerosol-induced cloud changes for the near future 2030 to present day time period may decrease O 3 forcing by up to 20% globally (Menon et al, 2008a). Therefore such cloud-aerosol-chemistry interactions warrant further examination.…”

The role of scavenging in the seasonal transport of black carbon and sulfate to the Arctic

“…Alongside atmospheric dynamic processes [Overland et al, 1997;Chylek et al, 2009;Francis et al, 2009], aerosols can exert a broad range of important effects on arctic climatological [Menon et al, 2008] and ecological systems [Muir et al, 1992].…”

“…The combined short-term reaction of surface temperatures to these forcings is seasonally dependent, but roughly adds up to 1°C [Quinn et al, 2008;Menon et al, 2008]. In fact, it has been argued that carefully implemented policies aimed at aerosol emission reductions could provide a fairly immediate slowing of rapid Arctic warming and sea-ice melting [Bond and Sun, 2005;Quinn et al, 2008].…”