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The increase in high-resolution proxy records over expanding areas of the globe helps deepen understanding of the unusual climate patterns-and the forcing mechanisms responsible for them-during the years 950 to 1400.
Climate in medieval times, a period usually un- derstood to extend from A.D. ~950 to ~1400, is of considerable interest to students of modern and future climate. This is because the period differs from recent centuries mainly by predating the Industrial Revolution with its associated changes in the composition of the atmosphere and oceans and the nature of the land surface (Hughes and Diaz 1994; Crowley and Lowery 2000; Bradley et al. 2003a,b). In this sense it represents an appealing, but imperfect "control case" for the unintended global climate experiment that has resulted from industrial and agricultural development and population growth.
In order to stimulate a synthesis of recent work on these topics, we convened a meeting of international experts to consider the following issues:
1) What were some of the key regional patterns of climatic anomalies during medieval times derived from the proxy climate records and from model simulations, and how do they compare with the twentieth-century patterns?
2) Recognizing that multiple proxy climate records are needed to constrain as much as possible the spatial and temporal variability of climate, what do recent studies using powerful statistical methods tell us about the timing and geographic coverage of the major features of climate in medieval times?
3) A number of numerical simulations using climate models of varying complexity and external forcing histories have been completed in the past few years. What do the latest model results tell us about geographic patterns and temporal characteristics of the simulated climate of this period?
4) In what specific ways does the climate of the last several decades (approximately the last 30 years) differ from periods of comparable length in medieval times?
HISTORICAL BACKGROUND. Hubert Lamb wrote first of a "medieval warm epoch" and later of a "medieval warm period," ending in A.D. 1300, when the relative frequency of warm episodes increased, primarily around the North Atlantic [see Lamb 1965 (p. 26), 1966, 1977, 1982]. He emphasized that this took place in a context of complex climate variability, varying by season and location. He worked primarily by...