Posted on 01/29/2008 11:13:13 AM PST by E. Pluribus Unum
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A Global Temperature History of the Past Two Millennia
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.
Reviewed 30 January 2008
The National Science Foundation investigaterd the Algore version of history (which emasculates the little ice age), and said it is not inconsistent with the data. This is not an affirmation. This is a statement that the UN was in the no man’s land between science and fraud. The NAtional Science Foundation then adopted something like this version of history (with the little ice), and the clear implication that we are currently in a not unusual warming phase in the hsitory of the world. As to whether human activity is ADDING TO this warming phase remains a legitimate question.
Looks like an oscillation with around a 1300 year cycle. What with data we’re seeing about variations in solar output, I’m thinking there may be more coming from solar output oscillation than any human cause
First impressions: Looking at the map of locations, it says there are 18 series, but I only count 15. There are likely more than one series from a couple of locations. Based on what I can see, 7 out of the 15 are extra-tropical in either North America, the North Atlantic, or Europe. So this area is over-represented and the Northern Hemisphere is over-represented.
Why is this important? Because previous work on the Medieval Warm Period has indicated that it was primarily a Northern Hemisphere event strongest in North America and Europe. (The LIA was more global.) So seeing it (a warming event occurring over about 400 years) in this data is not surprising.
2. Got this from Climate Audit, actually (which is instructive, 320 comments in the "Loehle Correction" thread). His last actual data point is 1935 (which is where his corrected Figure 2 ends). If you read the last paragraph of the correction, the difference between MWP and "end of 20th century values" is not significant. He calculated end-of-20th-century using a GISTEMP addendum, it appears.
3. What is significant? The warming rate. Reading Figure 1 roughly, the temperature increase is about 0.6 C in 400 years (I put the peak at about 900 AD). The warming rate in the 20th century was 0.6 C in 100 years, and the rate in the past 25 years was 0.4 C, which is 1.6 C in 100 years. So while comparing peak temperatures is a fun exercise, the rate of warming observed since 1900 is much faster than the rate of warming to the peak of the MWP.
Intriguing pattern: there is a big up and down temperature excursion right after 900 AD. I'd really like to see if that has a global signature or if it was regional.
Comments on "Loehle Correction" (Climate Audit)
Skimming, I note posts 16, 69 (Loehle is skeptical of rates, so I should be too), 95, 199, 203, and 301.
Ping
“Why is this important? Because previous work on the Medieval Warm Period has indicated that it was primarily a Northern Hemisphere event strongest in North America and Europe. (The LIA was more global.) So seeing it (a warming event occurring over about 400 years) in this data is not surprising.”
Current temperature models are primarily based on North American readings (most pervasive and “accurate”). Then there is the apples to oranges aspect to your retort - that being modern sampling techniques versus historical climate reconstruction. Consequently, the only possible comparisons are the peaks and valleys.
I’m calling BcoughULLcoughcoughSHcoughIcoughT.
I think we’re kind of stuck with mostly northern hemisphere data since there aren’t many good sampling locations down under.
The rate of increases are notable just because of their lack of periodicity yet the graphs show that each period of cooling began nearly precipitously which might make one question what shut off the cause of warming so suddenly.
Thanks for the ping!
INTERESTING!!!!
E-mail to Gore.
They had to change out their light bulbs too.......
We need too waterboard Al and get the real inconvenient truth.........
Actually, they DID NOT do that, and guess what.... THEY'RE ALL DEAD NOW!
Al Gore was RIGHT!
I agree that it’s not a very politic way to say it, but the quality of previous contributions to E&E with regard to AGW has been poor.
Really, are back were we always get too in this conversation:likely we will be tweaking the climatological history of the last 10,000 years for a while yet, but none of that changes the fact that to make AGW go away as an explanation for last 200 years of global warming you have to find some way to falsify the basic physics and chemistry of greenhouse effects. Which by this point is *highly* unlikely to happen - and in fact as far as I know no reputable observer is still making the attempt.
The question has now shifted to what *else* is going on, and at what time scale other natural processes are likely to either reverse or accelerate AGW.
And none of this is made any easier by the fact that AGW presents some real challenges to conservative political theory - at least in it’s recent US form - not the least of which is that there is no way address the problem unilaterally. The US (and everyone else) is just going to have to find a way to reach enforceable international agreements on carbon release, and many Americans on both the left and the right - for different reasons - are going to have a very* hard time coming to terms with that.
Is not the current warming trend also more pronounced in the Northern Hemisphere?
Yes. Land surfaces warm up considerable faster than the ocean, and there's a big difference between northern and southern hemisphere land area.
Actually, it's a blank check.
Global warming uber alles.
I sure am glad we have a super race of all-knowing people who will know exactly how to set the global thermostat.
Tree-rings
This study has excluded tree-ring data. But, it also didn’t include sun-spot data. We’ll have to accumulate excellent sun cycle data for the next two thousand years, that is if we want to get some valid results. That will show Algore he shouldn’t be making up science.
For the LIA cooling, sunspot numbers famously indicate solar activity minima that no doubt were a primary cause. I hazard an unschooled guess that the MWP resulted from variability of the thermohaline circulation. Reduced bottom water formation would allow more heat to stay in the atmosphere, and because the North Atlantic is where a lot of the bottom water forms, this would be the strongest area of impact.
But I don't think there's much I can produce to support that idea.
PING!
So in that respect the current warming trend is similar rather then dissimilar to the last one.
Thus whatever value your prior observation had, which probably isn't much, it would seem detrimental rather then helpful to the anthropological doctrine of the current trend.
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