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On its publication in September 2009, Kaufman et al (2009) “Recent Warming Reverses Long-Term Arctic Cooling” made its rounds in blogs.
The abstract reads, “The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.”
A BBC News article “Arctic 'warmest in 2,000 years'”…
http://news.bbc.co.uk/2/hi/science/nature/8236797.stm
…included the following graph:
http://i45.tinypic.com/2dcahd3.gif
Kaufman et al Graph In BBC Article
KAUFMAN et al PROXY DATA IS AVAILABLE FROM THE NOAA PALEOCLIMATOLOGY PROGRAM
NOAA Paleoclimatology Program includes a webpage for Kaufman et al (2009):
http://lwf.ncdc.noaa.gov/paleo/pubs/kaufman2009/kaufman2009.html
Toward the bottom of the page is a link to a spreadsheet that includes the standardized data of the 23 individual proxies included in Kaufman et al (2009):
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/reconstructions/arctic/kaufman2009arctic.xls
The last column (Column Y) in the spreadsheet is the average of the standardized proxies, which I’ve plotted below. Though the scales are obviously different, the curves of the BBC graph and the Average of the Standardized Proxies are similar in shape, a few minor differences, but they are similar.
http://i50.tinypic.com/2ptdpuv.png
Average Of Kaufman et al Standardized Proxies
The differences may reflect the October 2009 corrections made to 7 of the 23 proxies by Kaufman et al (noted in the spreadsheet). They included:
"October 2009 Update
"Record 2 was revised using the correct time scale of McKay et al. (S16)
"Record 12 was revised to omit the high-pass filter used by Andersen et al. (S25)
"Record 20 was corrected to reflect the interpretation of Tijander et al. (S32) that X-ray density is related inversely to temperature
"Record 21 was corrected to reflect the interpretation of Haltia-Hovi et al. (S33) that varve thickness is related inversely to temperature
"Records 3 and 10 were revised to correct rounding errors
"Record 19 was truncated at 1799 to exclude the 1805 bin, which was based on only one year (1800)"
In some respects, a spaghetti graph of the 23 proxies shows the same basic curve, but at least one of the proxies had higher values 2000 years ago and others appear to be dropping, not rising, in recent years.
http://i49.tinypic.com/4h9u6x.png
Spaghetti Graph Of Kaufman et al Standardized Proxies
That prompted me to plot the individual proxies to see what they revealed.
GRAPHS OF INDIVIDUAL PROXIES
The following are graphs of the 23 proxies used in Kaufman et al. There is a classic hockey stick, Proxy 22, which is a graph of the Briffa et al Yamal tree ring data. There’s also a reverse hockey stick, Proxy 12, which is the Andersen et al DYE3 South Greenland Ice Isotope data, where the upward blade is in the first few decades; then the curve remains relatively flat for the remainder of the term. Some of the datasets illustrate warmer temperatures in recent decades, Proxies 9 and 23. There are others that are relatively flat but there are many others that show warmer temperatures in centuries past. The graphs of the individual proxies follow, without commentary. The titles include the location, proxy type, author(s), and years covered.
http://i46.tinypic.com/120m4pe.png
Proxy 1
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http://i49.tinypic.com/o7vs51.png
Proxy 2
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http://i47.tinypic.com/1h6n9c.png
Proxy 3
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http://i50.tinypic.com/jtthtc.png
Proxy 4
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http://i47.tinypic.com/jpeura.png
Proxy 5
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http://i46.tinypic.com/35nbr85.png
Proxy 6
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http://i48.tinypic.com/aff40k.png
Proxy 7
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http://i48.tinypic.com/1pxb4p.png
Proxy 8
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http://i48.tinypic.com/2nki4g7.png
Proxy 9
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http://i48.tinypic.com/21kz8ye.png
Proxy 10
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http://i45.tinypic.com/2usfjp4.png
Proxy 11
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http://i48.tinypic.com/mx259k.png
Proxy 12
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http://i45.tinypic.com/2d77eih.png
Proxy 13
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http://i50.tinypic.com/34gn888.png
Proxy 14
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http://i50.tinypic.com/2qlgylx.png
Proxy 15
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http://i48.tinypic.com/eia1hj.png
Proxy 16
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http://i50.tinypic.com/xc3ipg.png
Proxy 17
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http://i48.tinypic.com/2mhv2xg.png
Proxy 18
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http://i47.tinypic.com/21kw4r8.png
Proxy 19
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http://i49.tinypic.com/24yn7nt.png
Proxy 20
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http://i45.tinypic.com/2eqevb8.png
Proxy 21
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http://i50.tinypic.com/2daej3b.png
Proxy 22
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http://i45.tinypic.com/2cnvbcy.png
Proxy 23
CLOSING
Viewed individually, the proxies do not necessarily illustrate “that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age,” or that the “cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.” Many of the proxies illustrate past temperatures rivaling or exceeding current temperatures and indicate long-term variability, not a long-term decline or pervasive cooling.
UPDATE 12-17-09: I modified the closing sentence with the addition of ...and indicate long-term variability, not a long-term decline or pervasive cooling.