Collaborative Research: Observationally-Constrained Estimates of Effective Radiative Forcing from Aerosol Radiation Interactions

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The solar heating of the Earth is affected by aerosols emitted from human activites including agriculture (for instance the burning of crop residue after the harvest), power generation (including both sulfate aerosol which reflects solar radiation and black carbon aerosol that absorbs it), and transportation. The radiative effects of these anthropogenic aerosols are hard to quantify, and their climatic effect is among the largest uncertainties in projections of future climate change. The goal of this project is to develop observationally-based estimates of the radiative forcing due to anthropogenic aerosols using the best available satellite and surface-based datasets. More specifically, the research seeks to produce estimates of the effective radiative forcing from aerosol-radiation interactions (ERFari), which includes both the radiative effects of the aerosols and the changes in radiative forcing due to changes in clouds brought about by aerosol radiative heating. For example, the heating due to absorption of solar radiation by black carbon aerosols (soot) can lead to the "burn off" of clouds, resulting in more sunlight reaching the ground. Data used to determine aerosol amounts, vertical profiles, and radiative parameters comes from several satellite missions ( (MODIS, the CALIPSO/CALIOP lidar, MISR, CERES) and from the ground-based AERONET network. The aerosol amounts and properties are used in combination with a radiative transfer model (MACR) to determine the aerosol radiative forcing. The radiative forcing is then used as an input to global climate models, from which estimates of the further impact of aerosols on cloud radiative forcing are determined. Model-derived estimates of the cloud radiative properties are then compared to further satellite cloud observations. A key assumption of the project is that fine-mode aerosols can be used as a proxy for anthropogenic aerosols, provided that known natural sources of fine-mode aerosol (dust, marine sulfate, sea salt) can be factored out. The work has broader impacts due to the potential importance of anthropogenic aerosol as a regional and global climate forcing. Work to reduce the large uncertainty in this climate forcing could lead to better projections of future climate change and its impacts on human activities. In addition, the project would support a graduate student and provide a research opportunity for an undergraduate student at an ethnically diverse university. One of the PIs also performs outreach to local K-12 students through a local nonprofit organization.