A Simple Model of Global Aerosol Indirect Effects

Journal Article · Fri Jun 28 04:00:00 EDT 2013 · Journal of Geophysical Research. D. (Atmospheres), 118(12):6688–6707

DOI:https://doi.org/10.1002/jgrd.50567· OSTI ID:1091441

Ghan, Steven J.; Smith, Steven J.; Wang, Minghuai; Zhang, Kai; Pringle, K. J.; Carslaw, K. S.; Pierce, Jeffrey; Bauer, Susanne E.; Adams, P. J.

Most estimates of the global mean indirect effect of anthropogenic aerosol on the Earth’s energy balance are from simulations by global models of the aerosol lifecycle coupled with global models of clouds and the hydrologic cycle. Extremely simple models have been developed for integrated assessment models, but lack the flexibility to distinguish between primary and secondary sources of aerosol. Here a simple but more physically-based model expresses the aerosol indirect effect using analytic representations of droplet nucleation, cloud and aerosol vertical structure, and horizontal variability in cloud water and aerosol concentration. Although the simple model is able to produce estimates of aerosol indirect effects that are comparable to those from some global aerosol models using the same global mean aerosol properties, the estimates are found to be sensitive to several uncertain parameters, including the preindustrial cloud condensation nuclei concentration, primary and secondary anthropogenic emissions, the size of the primary particles, the fraction of the secondary anthropogenic emissions that accumulates on the coarse mode, the fraction of the secondary mass that forms new particles, and the sensitivity of liquid water path to droplet number concentration. Aerosol indirect effects are surprisingly linear in emissions. This simple model provides a much stronger physical basis for representing aerosol indirect effects than previous representations in integrated assessment models designed to quickly explore the parameter space of emissions-climate interactions. The model also produces estimates that depend on parameter values in ways that are consistent with results from detailed global aerosol-climate simulation models.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1091441
• Report Number(s): PNNL-SA-93538; KP1703010
• Journal Information: Journal of Geophysical Research. D. (Atmospheres), 118(12):6688–6707, Journal Name: Journal of Geophysical Research. D. (Atmospheres), 118(12):6688–6707
• Country of Publication: United States
• Language: English

Related Subjects

aerosol
clouds
cycle
global
hydrologic
model