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REVIEWS OF GEOPHYSICS, VOL. 42, RG2002, doi:10.1029/2003RG000143, 2004

Climate over past millennia

P. D. Jones

Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, UK

M. E. Mann

Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA

Abstract

We review evidence for climate change over the past several millennia from instrumental and high-resolution climate “proxy” data sources and climate modeling studies. We focus on changes over the past 1 to 2 millennia. We assess reconstructions and modeling studies analyzing a number of different climate fields, including atmospheric circulation diagnostics, precipitation, and drought. We devote particular attention to proxy-based reconstructions of temperature patterns in past centuries, which place recent large-scale warming in an appropriate longer-term context. Our assessment affirms the conclusion that late 20th century warmth is unprecedented at hemispheric and, likely, global scales. There is more tentative evidence that particular modes of climate variability, such as the El Niño/Southern Oscillation and the North Atlantic Oscillation, may have exhibited late 20th century behavior that is anomalous in a long-term context. Regional conclusions, particularly for the Southern Hemisphere and parts of the tropics where high-resolution proxy data are sparse, are more circumspect. The dramatic differences between regional and hemispheric/global past trends, and the distinction between changes in surface temperature and precipitation/drought fields, underscore the limited utility in the use of terms such as the “Little Ice Age” and “Medieval Warm Period” for describing past climate epochs during the last millennium. Comparison of empirical evidence with proxy-based reconstructions demonstrates that natural factors appear to explain relatively well the major surface temperature changes of the past millennium through the 19th century (including hemispheric means and some spatial patterns). Only anthropogenic forcing of climate, however, can explain the recent anomalous warming in the late 20th century.

Received 20 October 2003; accepted 17 February 2004; published 6 May 2004.

Index Terms: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 1620 Global Change: Climate dynamics (3309); 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854).

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Citation: Jones, P. D., and M. E. Mann (2004), Climate over past millennia, Rev. Geophys., 42, RG2002, doi:10.1029/2003RG000143.

Copyright 2004 by the American Geophysical Union.