18.104.22.168 Industrial Era Sulphate Aerosols
Ice core data from Greenland and the mid-latitudes of the NH (Schwikowski et al., 1999; Bigler et al., 2002) provide evidence of the rapid increase in sulphur dioxide emissions (Stern, 2005) and tropospheric sulphate aerosol loading, above the pre-industrial background, during the modern industrial era but they also show a very recent decline in these emissions (Figure 6.15). Data from ice cores show that sulphate aerosol deposition has not changed on Antarctica, remote from anthropogenic sulphur dioxide sources. The ice records are indicative of the regional-to-hemispheric scale atmospheric loading of sulphate aerosols that varies regionally as aerosols have a typical lifetime of only weeks in the troposphere. In recent years, sulphur dioxide emissions have decreased globally and in many regions of the NH (Stern, 2005; see Chapter 2). In general, tropospheric sulphate aerosols exert a negative temperature forcing that will be less if sulphur dioxide emissions and the sulphate loading in the atmosphere continue to decrease.