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## MXD Age Based Variance

Posted by Jeff Id on January 22, 2014

I woke up the other day wondering if age of a tree would cause a different latewood density response to environmental factors.   I don’t remember reading anything about it so it seemed worthwhile to check.

I am working with 124 tree samples from the Polar.mxd file here.   This is the same data from my previous post.     I took each MXD curve which we showed previously has a long term age related signal and filtered that curve with a 51 year lowpass Gaussian filter.   The top of figure 1 shows the original curve (black) and the filtered curve (red).  Subtracting the red curve from the black curve gives the HF signal in the second pane of Figure 1 immediately below.  Basically a flat squiggly line.

I took all of the 124 trees and did the same thing.   Then I took the average for each year and calculated the confidence interval from the flattened high frequency curves.  The two sigma CI expands in a trumpet bell shape (dark gray) like the previous post so we know that differences in long term trend weren’t causing the whole shape.   The second pane below is the simple standard deviation (blue line).   Visually it has no appreciable trend over time meaning that as the trees age and gain mass, the response to 50 year and shorter signals isn’t a function of the age of the tree.     The trumpet bell shape of the dark gray region is therefore due to less samples in the older years and we don’t need to correct MXD variance for tree age.  It’s kind of a lame result, but at least we know the MXD answer.

1. ### timetochooseagainsaid

Dumb question probably, but any particular reason to choose 51 years?

• ### Jeff Idsaid

Nothing besides it being big enough that it won’t tweak short term changes much and an odd number.

• ### timetochooseagainsaid

Have you experimented with other slightly smaller or slightly larger numbers?

I don’t mean to be annoying or nitpicky, it’s just I would like to know for sure whether arbitrary decisions impact the results in any way.

Also it looks kind of like there is variance dependence on age as well as mean dependence. But something tells me this is probably just the number of trees drops off beyond a certain age?

2. ### Carricksaid

I think one explanation of these results is there is no coherent information in the high-frequency portion of the proxy records. Agree?

• ### Jeff Idsaid

Sorry for the slow replies everyone.

Phi has made the claim that this particular data does have good high frequency information and the additional claim that we should then assume low frequency is good as well. That is what has me doing this so we shall see.

3. ### Anonymoussaid

Jeff, having long given up on my blog I just wanted to thank you for continuing your interesting posts. Generally now a lurker, I usually don’t comment. This comment doesn’t have to do with this post, so sorry about that. But just wanted to offer a quick note on the HadCrut temperature anomalies. We’re now at 16 years and 6 months going back on a linear fit with no warming. December anomaly was 0.475. Just for kicks I played with the next month to see whether we can expect it to extend out next month.

To stay at 16 years, 6 months, the next anomaly needs to fall between .422 and .468. To add one month to the trend, between .383 and .421. To add two months, .206 and .382. And, just because we’ve been freezing our nads off all month, I went one further. Between -.012 and .205 would add 3 months. I’m sure the Hadley Center would never let that happen, but just in case…

Anyway, totally random offering, I know. Take care.

• ### Jeff Idsaid

Good to hear from you Joe. A few years ago I would have guessed that the warming trend would have steepened by now. At some point it should do a little more.

4. ### Anonymoussaid

Guess I’m not signed in. FYI, above comment by Joe @ Digital Diatribes.

5. ### CoRevsaid

My suspicion is that the GW alarmists are ignoring the Ice Core stories as they do not support the storyline. A cursory visual look at the Greenland and Antarctic data sets would match reasonably close for a long term study Does anyone know of a study that has tried to develop a Holocene-long, global-wide temperature trend using the set of ice core datasets?