Posted by Jeff Id on October 16, 2010
I continue to learn new details of paleoclimate. The Ljungqvist proxies have been great fun so far. I can’t plot them individually because some are confidentially revealed but I can average them. One surprise I had was when I took all tree proxies and all non-tree proxies and created nearly identical reconstructions. I mean these things are as noisy as any proxy series I’ve ever encountered but the average keeps coming out the same!
I ran a test today where I randomly selected series from the Ljungqvist series and created non correlation sorted composite plus scale reconstructions from them. This non-sorted CPS scales proxies according to their entire series length and averages. Basically it is a process which cannot create the ‘calibration period’ distortions encountered in Mannian regress-o-matic stuff. If you are non-mathematical, think of the following plots as reasonable averages of subsets of the data.
My previous Ljungqvist replication is here:
In the past, we’ve seen other’s math create hockey sticks from random data with no signal. Ljungqvist’s math and the following will create a statistically flat line from a truly random dataset whereas correlation sorted data or regression will create a hockeystick. The following is reasonable math with Ljungqvist temperature proxies.
So in this post, I scaled all proxies to zero mean and 1 for SD for their entire timeframe. I then selected random numbers of proxies to see what the true range of reconstructions that could be generated from them.
Below is a plot of 5o reconstructions created from selection of approximately 9 random proxies for each one. Red line is the mean of all series in the following plots. The red curve is a constant throughout this post.
The red line is the average, the grey mass is the 50 reconstructions plotted on top of each other. Think of the gray as an uncertainty of perfectly known data rather than an uncertainty of possibility. Expanding the graph to 500 series illustrates that the visible pattern is quite repeatable.
Note that we have an amazingly similar pattern. A multi color 20 series version is below.
Lets go more extreme. 5 series about 5 at a time.
Again, much of the general shape is repeated. Certainly these five are more flat on average than might be expected, you have to look at individual series to see my point.
I then plotted no dendro and dendro proxies.
It appears to me that the signal in this data is fairly consistent throughout the series. Looking at raw proxies, it is hard to see anything worthwhile but the averages always work. It seems that any potential critique of Ljundqvist would have to come from the source data itself and the source data has a number of independent origins.
These proxies appear less noisy than the Mannian ones so I correlated the series with CRU and plotted the histogram of the correlations below.
Remarkably, only 8 of the 30 proxies had less than a 0.1 correlation to temp 22% whereas Mann08 the proxies had over 60% with less than 0.1 correlation to temp. I’m not sure what to make of all this, there isn’t much in Ljungqvist10 on proxy selection processes but they are obviously a more consistent set than Mann08.