Comments on: Jones et al [1998]: Gridcell Correlations

By: David Stockwell

David Stockwell — Wed, 21 Sep 2005 15:15:04 +0000

#34 And relevant to todays hot thread on treelines, while averages of tree cores have expectation of zero temperature signal, the methodology is probably not ‘foxable’, a treeline proxy would not suffer from the same cancellation problem, as we would expect treeline response to roughly linear with temperature.

By: JerryB

JerryB — Wed, 21 Sep 2005 15:01:01 +0000

Steve, or John A,

In case you do not get to review yesterday’s comments, let me mention that some comments by Mike Hollinshead were deleted from this thread yesterday between comments 14 and 18.

It seems that he exceeded Spam Karma’s new visitor first day threshold.

By: TCO

TCO — Wed, 21 Sep 2005 15:00:30 +0000

Agreed.

By: David Stockwell

David Stockwell — Wed, 21 Sep 2005 14:00:02 +0000

#31 TCO, yes you could try that, and attempt to use all trees, but the following problems come to mind. First you have to know the optimal temperature and response curve for each species, and the position of each tree relative to that. Also, temperature is only one factor defining optimal habitat. The more parameters you need in your model, the more potential errors you incorporate, and more data required. Not saying you couldn’t with a great deal of selection or additional information calibrate a more complex model, just that one wouldn’t expect a temperature signal from a simple model using a parabolic proxy.

By: TCO

TCO — Wed, 21 Sep 2005 13:52:16 +0000

Why is the station data not available (short the names of people). Is it still a privacy concern (if exact locations are given maybe)?

What is the source for the gridcell temps in that other record (the stations)? Who did the construction? Still seems like a worthwhile test to look at how that series tends to move with version and interact with proxies, versus the JOnes CRUs (if you want to snoop for possible finagling by Jones).

By: TCO

TCO — Wed, 21 Sep 2005 13:48:20 +0000

Did you follow what I meant with the multiple regression comment? The implication is that with extra equations, you can solve for extra unknowns. It’s an algebra concept and is reasonable (not cherrypicking). Basically, in “Dave’s model world”, I would just record elevation and note that the areas on the “too hot zone” were getting worse and on the “too cold zone” were getting better during any warming period.

Steve can back me up here. I’m not doing anything snaky here. The algebra issue is that in your model world, we have a quadratic response to temp, so that I need to solve a regression for both t and tsq. HAving the extra elevation variable allows me to do that.

Slight pedant point: if RW, MXD are both collected (and differ in their reaction to temp) that may also allow me to deconvolute your conundrum. But elevation recording and input into the model is the obvious method.

By: Steve McIntyre

Steve McIntyre — Wed, 21 Sep 2005 13:45:27 +0000

It’s the station data that’s not available – the gridcell information is available.

By: David Stockwell

David Stockwell — Wed, 21 Sep 2005 13:40:36 +0000

That is my point. The theoretical model predicts that in the real world, extracting a temperature signal from trees in environments of variable optimality REQUIRES selection, or call it ‘cherry picking’. There is no apriori reson to expect dendroclimatology to produce a reliable climate signal from a random sample of trees. This is not the case however with other proxies such as glacier length or isotope ratios where one expects, apriori, the response to be linear with temperature not parabolic as is the case with trees.

By: JerryB

JerryB — Wed, 21 Sep 2005 13:34:50 +0000

Louis,

First, let me clarify the question: “is there an alternate?”.

When Steve wrote: “Jones gridcell temperature data is still private.”, his wording was open to multiple interpretations. When he added: “Warwick Hughes has tried hard to get it without success.”, he narrowed the possible interpretations to (land based) suface station temperature data. (Other kinds of “Jones gridcell temperature data” are publicly available.)

One collection of land based surface station temperature data that is publicly available is called GHCN (Global Historical Climatology Network). A brief overview of GHCN is available at http://www.ncdc.noaa.gov/oa/climate/research/ghcn/ghcnoverview.html

Caveat: any such collection includes problematic data.

By: TCO

TCO — Wed, 21 Sep 2005 13:22:37 +0000

Just reread your post. I guess in your model world, with your model methods that would be the result. However, there is no reason for a real researcher to be so constrained (e.g. to “random coring” or (implicitly) to not inlcuding locational issues (e.g. elevation) as a variable within a multiple regression). And there is no reason why your trees have to be situated in such a manner or have such a response.