A Global Temperature History of the Past Two Millennia

Mean relative temperature history of the globe. Adapted from Loehle (2007).

Download original science paper here.

A Global Temperature History of the Past Two Millennia

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Reference
Loehle, C. 2007. A 2000-year global temperature reconstruction based on non-treering proxies. Energy and Environment 18: 1049-1058.

What was done
Using data from eighteen 2000-year-long proxy temperature series from all around the world that were not developed from tree-ring data (which provide significant interpretive challenges), the author (1) smoothed the data in each series with a 30-year running mean, (2) converted the results thereby obtained to anomalies by subtracting the mean of each series from each member of that series, and then (3) derived the final mean temperature anomaly history defined by the eighteen data sets by a simple averaging of the individual anomaly series, a procedure that he rightfully emphasizes is "transparent and simple."

What was learned
The results obtained by this procedure are depicted in the figure below, where it can be seen, in the words of its creator, that "the mean series shows the Medieval Warm Period (MWP) and Little Ice Age (LIA) quite clearly, with the MWP being approximately 0.3°C warmer than 20th century values."

What it means
Loehle notes that "the 1995-year reconstruction shown here does not match the famous hockey stick shape," which clearly suggests that one of them is a poorer, and the other a better, representation of the truth. Because of its simplicity and transparency, as well as a host of other reasons described in detail by Loehle -- plus what we have learned since initiating our Medieval Warm Period Record-of-the Week feature -- it is our belief that Loehle's curve is by far the superior of the two in terms of the degree to which it likely approximates the truth.

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Bottom Line: There have been two periods during the past 2,000 years that were warmer than today. -- Both shown on the graph at the top. This historical temperature reconstruction only spans 2,000 years. If the scope were widened to the end of the last ice age, the Holocene climatic optimum, about 5,000 to 9,000 years before present, the temperature record would show even warmer temperatures.

The AGW proponents use a single temperature proxy, tree-rings, to predict global catastrophe. This article uses the average of 18 temperature proxies for the past two-thousand years.

Any time an enviro-wacko calls you a global-warming denier, wave this article in their face and ask them to refute it. If there isn't any global warming, there isn't any anthropogenic component either.

More here at ICECAP.