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Climate Over Past Millennia

Figure 5a compares a number of different NH estimates over the past 1000 years.
Figure 5a. compares a number of different NH estimates over the past 1000 years
Climate Over Past Millennia
Reviews of Geophysics,
Vol. 42, No. 2, RG2002, doi:10.1029/2003RG000143,
6 May 2004.

P.D. Jones1 and M.E. Mann2
1 Climatic Research Unit School of Environmental Sciences University of East Anglia Norwich, UK
2 Department of Environmental Sciences, University of Virginia, Charlottesville VA, USA
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.

Download the data from the figures in this study:

Data Description
figure 2c  Instrumental temperature, 20-year smoothed annual average values for N.Hemisphere, central Europe, Fennoscandia, and central England.
figure 4a  Proxy temperature reconstructions, Western North America
figure 4b  Proxy temperature reconstructions, North Atlantic
figure 4c  Proxy temperature reconstructions, Europe
figure 4d  Proxy temperature reconstructions, Eastern Asia
figure 4e  Proxy temperature reconstructions, Tropics
figure 4f  Proxy temperature reconstructions, Tasmania
figure 5  Global/Hemispheric mean annual temperature reconstructions
figure 6a  Reconstructions of the Southern Oscillation Index (SOI)
figure 6b  Reconstructions of the North Atlantic Oscillation (NAO)
figure 7  Estimates of natural and anthropogenic radiative forcings
figure 8  Model-based estimates of N.Hemisphere temperature variations

Re-Scaled   Jones-Mann 2004 N.Hemisphere temperature reconstruction
to the same decadal standard deviation as the instrumental record over the 1856-1995 period.

To read or view the full study, please visit the AGU website.
It was published in Reviews of Geophysics Vol. 42, No. 2, RG2002, doi:10.1029/2003RG000143, 6 May 2004.

P.D.J. acknowledges support of the Office of Science (BER), U.S. Department of Energy, grant DE-FG02-98ER62601. P.D.J. also acknowledges the Climate Change Detection and Attribution Project, a jointly funded effort by NOAA's Office of Global Programs and the Department of Energy's Office of Biological and Environmental Research. M.E.M. acknowledges support for this work by the NSF and NOAA-sponsored Earth Systems History (ESH) program (NOAA award NA16GP2913).

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8 December 2004