The Anthropogenic Era

Anthropogenic influences on climate and atmospheric chemistry have been preliminarily investigated in the GISP2 record. Previously identified increases in sulfate and nitrate seen in south Greenland ice cores and attributed to anthropogenic activity [ Neftel et al., 1985; Mayewski et al., 1986] have been identified in the GISP2 core and contrasted to the pre-anthropogenic atmosphere [ Mayewski et al., 1990]. Although year-to-year variability may be largely dominated by variability in atmospheric circulation, Mayewski et al. [1990] demonstrated that background concentrations in the remote atmosphere maintain a signature that responds to, at the very least, patterns in the strength of pollutant sources on scales on the order of decades or less. While pre-anthropogenic concentrations of nitrate exceeded those of sulfate, by the turn of the nineteenth century sulfate levels caught up to nitrate levels in response to dramatic increases in the emissions of pollutant SO. By the mid-1970s, however, nitrate concentrations again exceeded sulfate concentrations, reflecting the more rapid rise of NO pollutant emissions. An observed increase in excess chloride at GISP2 [ Mayewski et al., 1993a] as of the 1940s, is believed to be a byproduct of the increased levels of anthropogenically-derived HNO and HSO, since the latter are believed to aid in the volatilization of HCl from seasalt aerosol [ Eriksson, 1959]. Additional confirmation of the role that anthropogenic pollutants may have on perturbing the chemistry of the atmosphere comes from the coincidence of increased sulfate levels and depression of North Atlantic temperatures between 1940-1970 [ Wigley, 1990; Charlson et al., 1992] which has been demonstrated by a comparison of GISP2, south Greenland and Yukon Territory ice cores with temperature change records [ Mayewski et al., 1993b].

Examination of a 217-meter temperature profile developed from a site near the GISP2 borehole reveals a recent warming in near-surface firn which is within the range of natural variability, providing no definitive evidence of anthropogenically-induced greenhouse gas warming [ Alley and Koci, 1990].