Paleoclimate Temperature Reconstructions: Implications for Climate Change

Global warming is an issue that has gathered much public, legislative, national and international attention and has caused considerable friction among governments and among their citizens. The IPCC report (Intergovernmental Panel on Climate Change, 2001) entitled, Climate Change 2001: Third Assessment Report, featured alarming statistics concerning the rapid rise in global temperatures during the decade of the 1990s and suggested that this rapid rise was due principally to anthropogenicly generated greenhouse gas emissions, specifically carbon dioxide. This document was taken to be a strong justification for the Kyoto Accord. Featured prominently in the IPCC report was the work of Mann and his colleagues (Mann et al., 1998, 1999) (MBH98, MBH99). These papers featured temperature reconstructions going back as far as 1000 years. The methodology found in Mann et al. was a statistical methodology known as principal components analysis (PCA). Challenges to the way in which PCA was used have arisen from McIntyre and McKitrick (2003, 2005a, 2005b). The challenges are based on rather subtle mathematical nuances. Climate change of course has major implications for public health in terms of spread of disease vectors, potential species loss, and increased extreme weather events.