Northern Hemisphere average surface temperature

Mann et al. (1999) Geo. Res. Let. 26(6):759.

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Caption: This figure forms the basis for the claim that 1998 was the warmest of the millennium at that time in the Northern Hemisphere, even when full account is taken of the increasing uncertainties associated with reconstructions of individual years prior to AD 1600. The reconstruction also indicates that there are statistically valid links between pre-20th century temperature variability and both solar and volcanic forcing, whereas during recent decades, there is every indication of an increasingly strong correlation between the temperature trend and the influence of atmospheric CO2.

Mann, M. et al (1999) Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties and Limitations, Geophysical Research Letters, 26, 6, p.759