Fig. 5. Comparison of STD and RCS NH reconstructions with mean annual land
(20°N-90°N) temperatures.
Top: Annual time series from 1200 AD.
Bottom: 20-year smoothed time series from 1200 AD.
Click image for full figure, time series from 713AD.
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On the long-term context for late twentieth century warming
Journal of Geophysical Research - Atmospheres
Vol. 111, No. D3, D03103, doi:10.1029/2005JD006352, 07 February 2006.
Rosanne D'Arrigo1, Rob Wilson 2, Gordon Jacoby1
1 Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, New York, USA
2 School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh, UK
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ABSTRACT:
Previous tree-ring-based Northern Hemisphere temperature reconstructions
portray a varying amplitude range between the "Medieval Warm Period"(MWP),
"Little Ice Age" (LIA) and present. We describe a new reconstruction,
developed using largely different methodologies and additional new data
compared to previous efforts. Unlike earlier studies, we quantify differences
between more traditional (STD) and Regional Curve Standardization (RCS)
methodologies, concluding that RCS is superior for retention of low-frequency
trends. Continental North American versus Eurasian RCS series developed
prior to merging to the hemispheric scale cohere surprisingly well,
suggesting common forcing, although there are notable deviations
(e.g., fifteenth to sixteenth century). Results indicate clear MWP (warm),
LIA (cool), and recent (warm) episodes. Direct interpretation of the RCS
reconstruction suggests that MWP temperatures were nearly 0.7C cooler than
in the late twentieth century, with an amplitude difference of 1.14C from
the coldest (1600-1609) to warmest (1937-1946) decades. However, we advise
caution with this analysis. Although we conclude, as found elsewhere, that
recent warming has been substantial relative to natural fluctuations of the
past millennium, we also note that owing to the spatially heterogeneous
nature of the MWP, and its different timing within different regions,
present palaeoclimatic methodologies will likely "flatten out" estimates
for this period relative to twentieth century warming, which expresses
a more homogenous global "fingerprint." Therefore we stress that presently
available paleoclimatic reconstructions are inadequate for making specific
inferences, at hemispheric scales, about MWP warmth relative to the present
anthropogenic period and that such comparisons can only still be made at
the local/regional scale.
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