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Tree Ring Reconstruction of
the Last 1,000 Years
Michael E. Mann and Raymond S. Bradley of the Department of Geosciences, University of
Massachusetts and Malcom K. Hughes of the Laboratory of Tree-Ring Research, University of
Arizona reconstruct Northern
Hemisphere temperatures during the past millennium by building on recent studies
using various proxy data networks. They have examined both mean values and uncertainties
in the proxy data. Large uncertainties prior to AD 1400 preclude definitive statements
for that period. However, their results suggest that the last 100 years of the 20th century is anomalous
in the context of at least the past thousand years. The decade of the 1990s was the
warmest of the record, and 1998 the warmest year, at moderately high levels of confidence.
The 20th century warming represents an abrupt and opposite change from the pre-existing
millenial-scale cooling trend that is consistent with long-term astronomical forcing.
NEXT: Fossil Pollen and Glacial Termini
