Reply #47: Here's yer 1000 year temperature data - read it and weep...

[jpak]

http://www.nature.com/nature/journal/v376/n6536/abs/376156a0.html

Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia

Keith R. Briffa, Philip D. Jones, Fritz H. Schweingruber, Stepan G. Shiyatov & Edward R. Cook

Abstract

In the current debate on the magnitude of modern-day climate change, there is a growing appreciation of the importance of long, high-resolution proxies of past climate1–3. Such records provide an indication of natural (pre-anthropogenic) climate variability, either singly at specific geographical locations or in combination on continental and perhaps even hemispheric scales4. There are, however, relatively few records that are well dated, of high resolution and of verifiable fidelity in terms of climate response, and conspicuously few that extend over a thousand years or more5. Here we report a tree-ring-based reconstruction of mean summer temperatures over the northern Urals since AD 914. This record shows that the mean temperature of the twentieth century (1901–90) is higher than during any similar period since AD 914.

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Thomas J. Crowley (2000) Causes of Climate Change Over the Past 1000 Years. Science, 289: 270-277.

Abstract:

Recent reconstructions of northern hemisphere temperatures and climate forcing over the last 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparison of observations with simulations from an energy balance climate model indicate that as much as 41-64% of pre-anthropogenic (pre-1850) decadal-scale temperature variations were due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to control runs of coupled models, thereby lending support to the models' value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the ~1000 year time series results in a residual with a very large late 20th century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st century global warming projection far exceeds the natural variability of the last 1000 years and is greater than the best estimate of global temperature change for the last interglacial.

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Jones, P.D. and M.E. Mann (2004) "Climate Over Past Millennia." Reviews of Geophysics, Vol. 42, No. 2, RG2002, doi:10.1029/2003RG000143, 2004

This collection of Northern Hemisphere temperature reconstructions is from a variety of studies, all based on high-resolution proxy data. The reconstructions are derived from different but in some cases, not entirely independent data sets. Some are based solely on extra-tropical continental data from tree rings, while others are based on multiple proxies, including tree rings, ice cores, corals, historical documents, and long instrumental records. Several are reconstructions of warm season temperatures and others are of annual temperatures. However, trends in low-frequency warm season temperatures have been shown to be very comparable to those in annual temperature. The reconstructions have been generated using a variety of statistical methods for treating the biological growth trends (standardization) in the tree-ring data to preserve the low-frequency variance, and calibrating proxy data with instrumental data to generate reconstruction models.

All five series are annually-resolved reconstructions of temperature change. They have been scaled against the smoothed instrumental records based on the period 1856-1980, except Briffa et al. 2001 (scaled to 1856-1940), and smoothed with a 40-year low pass filter (Jones and Mann 2004). While there are differences between the reconstructions due to the factors mentioned above, all, even the least similar, are in agreement in showing the strong increase in temperatures since early 19th century, with the highest temperatures in the past 1000 years occurring at the end of the 20th century. The robustness of this result is clearly supported by the range of data and methods used to generate these reconstructions. Since only one of these reconstructions extends back to the early part of the previous millennia, results are more tentative, but suggest the recent warming could be unprecedented in nearly 2000 years.



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any other questions???