Mann 08 Series Weight Per Year
Posted by Jeff Id on September 28, 2008
As many of you are aware I was able to reconstruct Mann 08 by back caclulation tachnique. I used the known output graph for the northern hemisphere as provided by mann and the proxies provided by Mann to determine weighting for each proxy — no easy task. But after many hours of work I came up with this graph.
It’s not a perfect reconstruction but I expect that is due to filtering and possible mismatches between the proxies provided and the ones actually used to make the above graph. The Blue line is my calculation.
It isn’t perfect but it is close. From the data behind this graph we can determine some interesting things. First, how many curves were used in recent times and historic times. The graph peaks at 138 proxies which is slightly different from my previous post due to a few tweaks to the iteration. From 0 to 1000 years have under 20 proxies which when I look at the scaling magnitude is really about 4 to 6.
This graph is pretty interesting considering Mann’s claim in his paper that the large numbers of proxies allow such good temperature reconstruciton.
The next graph is the most telling though. Which proxies were actually used to create the M08 curve. The vertical scale on this graph is percentage contribution of each series group. The groups were chosen according to M08 SD1 where Mann divided the proxies using a number i.e. 9000 = tree ring width.
This plot therefore depicts the contribution of each year from each type of data. The first thing I noticed is the light blue Luterbacher series which sits at the very bottom right corner of this graph. There were 71 proxies used in the M08 paper, every one was accepted by correlation to temperature because they actually are created using temperature. Skeptics like myself and others had expected that this insturmental data would be very heavily weighted to provide the best correlation to temp. The fun thing about science though is you often get to be wrong. It’s like being married. The Luterbacher group is actually weighted at less than 10 percent of the graph through most of its length. The very tip which isn’t visible near 2000 the graph spikes upward creating 70% of the total output at that point.
Even more interesting is the compiled tree ring width data. This is by far the most prevalent type of data in the record. Mann cut the tips off of many of these proxy series and pasted on a temperature curve. In other words he worked very hard to keep a bunch of data which didn’t appear to be temperature. But after the weightings are performed, all the tree ring data only affected the most recent 800 years.
Our results extend previous
conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent
warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used,
the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats.
I find this interesting considering hat the trees influence on the final result tapers off by about 1300 AD.
On another interesting item, the contribution of Punta Laguna proxies which are visible on the left side of the graph in light blue placed directly above an ever so slightly darker blue. The vertical scale of Punta laguna in these times is quite large. The graph itself made little contribution to recent times because its values were overwhelmed by the numbers of recent data. The yellow section directly above punta laguna is cave precip records and some other mixed proxies which were type 6001 on the Mann dataset.
I averaged the contribution of these two proxies for the 0-1000 year period and found that they represent no less than 74 percent of the total weight of the reconstruction for this 1000 year period.
Anyway many of my readers are probably more familiar with the individual proxies than I am. I just want to add, every time I look closer at this paper I find more reasons to doubt its conclusions.