Introduction

As discussed in Chapters 1 and 4, radiation forcing from stratospheric aerosols contributes to the variability of the climatic system. This chapter provides a detailed analysis of how these aerosols affect Earth's climate system. Stratospheric aerosols, in the aftermath of intense volcanic eruptions, can perturb substantially the climate of the stratosphere and surface–troposphere system (IPCC, 1995). Typically, the particulates appearing initially are comprised of silicates (e.g., ash). These are large (diameter greater than a few microns) and tend to fall off rapidly (within a few months) (Robock et al., 1995). The conversion of the sulfur-containing gases injected into the stratosphere to sulfate aerosols occurs in a few weeks to months. This results in a loading of the stratosphere with submicron sulfate aerosols having a residence time of one to two years. The radiative effects depend on the type, size, and shape of the particulates. While in the first several weeks, the radiative effects may be dominated by the ash particles, over the longer term (after a few months and up to ∼ two years) and of considerable relevance to climate, the sulfate aerosols dominate the effects. We focus on the effects due to sulfate aerosols in this study.

Sulfate aerosols possess absorption bands in both the solar and longwave spectra, and have significant scattering ability in the solar spectrum.