Climate Change 2001:
Working Group I: The Scientific Basis
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Figure 12.6: (a) Five-year running mean Northern Hemisphere temperature anomalies since 1850 (relative to the 1880 to 1920 mean) from an energy-balance model forced by Dust Veil volcanic index and Lean et al. (1995) solar index (see Free and Robock, 1999). Two values of climate sensitivity to doubling CO2 were used; 3.0°C (thin solid line), and 1.5°C (dashed line). Also shown are the instrumental record (thick red line) and a reconstruction of temperatures from proxy records (crosses, from Mann et al., 1998). The size of both the forcings and the proxy temperature variations are subject to large uncertainties. Note that the Mann temperatures do not include data after 1980 and do not show the large observed warming then. (b) As for (a) but for simulations with volcanic, solar and anthropogenic forcing (greenhouse gases and direct and indirect effects of tropospheric aerosols). The net anthropogenic forcing at 1990 relative to 1760 was 1.3 Wm-2 , including a net cooling of 1.3 Wm-2 due to aerosol effects.

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