[Moseley]

But even if tree ring data were not faked,

how do you calibrate tree rings as an instrument of precise scientific measurement?

how do you standardize it as an instrument of measure?

what is the margin of error in tree ring measurements?

isn’t the margin of error or range of imprecision far greater than the effects we are trying to calculate?

[bert]

I think tree rings are one of Blam’s areas of expertise

[CedarDave]

Tree rings measure the amount of yearly growth as a result of moisture received, not temperature. The assumption is that if you have a wide ring there was a lot of moisture in the spring when most tree growth occurs. Scientists assume that a moist spring (wide ring) means temperatures are cool and a dry spring (thin ring) means a warm spring.

The problem occurs when they try to extrapolate that to a year round temperature. For example, in the southwest where tree ring dating was first developed, you can have a moist cool spring but a hot dry summer. For that year you have a wide ring (growth mostly complete) and a hotter than normal summer. The reverse is also true - a dry spring and a wet summer due to the SW monsoons. It's obvious then that using tree rings as a indicator of temperature can be fraught with problems.

As for calibration, tree rings were originally calibrated against spring rainfall records for locations in the US southwest (Tucson area to begin with) and are used, for example, to show that a dry period occurred in the 1100-1200's that may have contributed to the abandonment of the large Indian pueblo culture of Chaco Canyon in northwest New Mexico. Again, relying on tree rings alone as a predictor of past temperature can result in false conclusions.

(BTW back in the ancient past, I took a semester course at the UofAZ and actually went out, collected tree rings, measured them and learned to correlate them with rainfall records.)

[CedarDave]

BTW, to answer your specific questions:

how do you calibrate tree rings as an instrument of precise scientific measurement?
Calibration is done with rainfall records in the area of interest.

how do you standardize it as an instrument of measure?
Only useful if you have recent rainfall records in the area studied.

what is the margin of error in tree ring measurements? isn’t the margin of error or range of imprecision far greater than the effects we are trying to calculate?
See my earlier reply that discusses limitations of the methodology.