Comments on: Loehle Proxies #2

By: realclimate on Loehle « Climate Audit

realclimate on Loehle « Climate Audit — Mon, 17 Jan 2011 12:06:54 +0000

[...] case, they cite information on Loehle that was initially made available at climateaudit. In this CA post, we discussed discussed the provenance of Loehle proxies and requested that Loehle provide his [...]

By: Laws of Nature

Laws of Nature — Mon, 09 Mar 2009 05:16:53 +0000

Great!!
Many thanks,
this should deal with that part of the argument!
The fact that it is also peerreviewed comes in handy – I totally underestimated how many good arguments could be stonewalled by ignorance..

All the best,
LoN

By: Craig Loehle

Craig Loehle — Fri, 06 Mar 2009 20:34:18 +0000

Re: Laws of Nature (#29), In my original paper I computed confidence intervals using bootstrap and jackknife methods. The long smoothing period is due to the widely spaced data in many proxies.

By: Hu McCulloch

Hu McCulloch — Fri, 06 Mar 2009 20:14:27 +0000

Re Laws of Nature #29,
Bender apparently still has Craig locked in his basement (inside joke ), so I’ll try to answer pending his release.

I worked with Craig to provide confidence intervals for his 2008 revision of his 2007 paper. See graphs and links at http://www.econ.ohio-state.edu/jhm/AGW/Loehle/.

The revision comes up to 1935 (based on a 29-year centered moving average of data that ends in 1950). This isn’t the present, but it overlaps the post-1850 instrumental period enough for you to splice it on to your favorite series. (Since it has been smoothed from that that extends up to 1950, it would make sense to make the link with a similarly smoothed version of the instrumental series you use.)

By: Laws of Nature

Laws of Nature — Fri, 06 Mar 2009 03:02:40 +0000

Dear Craig,

some quick questions which are most likely already discussed somewhere on this site:
Could you either point the answers out for me or (much better) write a new answer for me in laymen terms

Thanks a lot,

LoN (engaged in a private little Hockey-stick discussion)

First:
What would be your answer to the accusation, that your smoothed proxies don’t overlap with the instrumental reprod?
Second:
How would you calculate your confidence intervals?

I am sorry for writing this, since I am pretty sure, that I have seen you answering both questions somewhere, unfortunately this was a while ago and my google-fu is not good enough to bring it up.

By: Geoff Olynyk

Geoff Olynyk — Fri, 07 Dec 2007 17:29:23 +0000

RealClimate takes on Loehle 2007: link. The dating criticisms are pretty damning. Nice of them to link to JEG's personal blog for "further discussion" but not to any of the five CA threads on the matter, though.

By: Jaye

Jaye — Wed, 21 Nov 2007 02:43:17 +0000

A filter that rings I understand, smoothing to increase nyquist I don’t. A lowpass filter will reduce aliasing…all things being equal. Like I said it probably a semantic issue.

By: Pat Keating

Pat Keating — Wed, 21 Nov 2007 02:24:56 +0000

26
I think what he may be saying is that the edges of the averaging window will produce sidelobes [e.g., sine(x)/x] which add distortion. This is most serious if you have sharp peaks in the time-series and need fidelity near them. I don’t think that’s an issue here.
It can be ameliorated by using a window without sharp edges (e.g., a gaussian, but there are lots of other choices).

By: Jaye

Jaye — Wed, 21 Nov 2007 02:11:34 +0000

Smoothing aliases higher frequency data down into lower frequency bands. Extending the periods of the smooths, as indicated here would increase the aliasing frequency and tend to mitigate any problems that might arise.

I’m not really grokking those statements. Aliasing is a phenomenon determined by sampling rate. Smoothing a signal gives one more “room” between the nyquist frequency (due to sampling) and the max frequency of the signal. How that “increases the aliasing frequency” is not apparent to me…maybe this is a semantic thing.

By: Fred

Fred — Wed, 21 Nov 2007 00:45:34 +0000

Quick question: Why was Conroy Lake, ME chosen over Hells Kitchen Lake, WI? Both have a 2000 year record and it would seem that there is already an Eastern US member with the Chesapeake Mg/Ca. There is a big difference in the two series, with Conroy cooling significantly, and Hells Kitchen is pretty flat.