IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group I: The Physical Science Basis
Figure 9.4

Figure 9.4. Contribution of external forcing to several high-variance reconstructions of NH temperature anomalies, (Esper et al., 2002; Briffa et al., 2001; Hegerl et al., 2007, termed CH-blend and CH-blend long; and Moberg et al., 2005). The top panel compares reconstructions to an EBM simulation (equilibrium climate sensitivity of 2.5°C) of NH 30°N to 90°N average temperature, forced with volcanic, solar and anthropogenic forcing. All timeseries are centered on the 1500-1925 average. Instrumental temperature data are shown by a green line (centered to agree with CH-blend average over the period 1880-1960). The displayed data are low-pass filtered (20-year cutoff) for clarity. The bottom panel shows the estimated contribution of the response to volcanic (blue lines with blue uncertainty shade), solar (green) and greenhouse gas (GHG) and aerosol forcing (red line with yellow shades, aerosol only in 20th century) to each reconstruction (all timeseries are centered over the analysis period). The estimates are based on multiple regression of the reconstructions on fingerprints for individual forcings. The contributions to different reconstructions are indicated by different line styles (Briffa et al.: solid, fat; Esper et al.: dotted; Moberg: dashed; CH-blend: solid, thin; with shaded 90% confidence limits around best estimates for each detectable signal). All reconstructions show a highly significant volcanic signal, and all but Moberg et al. (which ends in 1925) show a detectable greenhouse gas signal at the 5% significance level. The latter shows a detectable greenhouse gas signal with less significance. Only Moberg et al. contains a detectable solar signal (only shown for these data and CH-blend, where it is not detectable). All data are decadally averaged. The reconstructions represent slightly different regions and seasons: Esper et al. (2002) is calibrated to 30°N to 90°N land temperature, CH-blend and CH-blend long (Hegerl et al., 2007) to 30°N to 90°N mean temperature and Moberg et al. (2005) to 0° to 90°N temperature. From Hegerl et al. (2007).