Note 21
From "Climate Change Natural" In Global Climate Explained

(a) Mann et al., 1998. "Global-scale Temperature Patterns and Climate Forcing over the Past Six Centuries," Nature , Vol. 392, pp. 779-787.

(b) M.E. Mann, R.S. Bradley, and M.K. Hughes, 1999. "Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations," Geophysical Research Letters, Vol. 26, No. 6, pp. 759-762.