Two Civil Conversations on Other Blogs
Posted by Jeff Id on October 1, 2010
I’ve been enjoying a couple of conversations away from tAV. One where I’m discussing with James Annon the McKitrick McIntyre and Herman paper which shows models far exceeding trends. His blog is moderated so the pace is very slow. The link is here. James has made (and published) the claim that model means produce a non-physical result and is therefore not worth examining closely. I replied that while model mean may be non-physical the magnitude of the difference is the issue. It has been a fun conversation to date.
The second conversation is more entertaining and has been over at Bart Verheggens open thread. We’ve been discussing the usual hockey sticks with unusual civility. Scott Mandia asked for the simplest explanation of why some critique the hockey sticks – so I took a crack at it below.
Temperature proxies are millenia long series of suspected but unknown temperature sensitivity among other things (noise). Other things include moisture, soil condition, CO2, weather pattern changes, disease and unexpected local unpredictable events. Proxies are things like tree growth rates, sediment rates/types, boreholes, isotope measures etc.
In an attempt to detect a temperature signal in noisy proxy data, today’s climatologists use math to choose data which most closely match the recently thermometer measured temperature (calibration range) 1850-present.
The series are scaled and/or eliminated according to their best match to measured temperature which has an upslope. The result of this sorting is a preferential selection of noise in the calibration range that matches the upslope, whereas the pre-calibration time has both temperature and unsorted noise. Unsorted noise naturally cancels randomly (the flat handle), sorted noise (the blade) is additive and will average to the signal sorted for.
The blade of the hockey stick is the sorted signal and noise in post 1850 times, the handle has a flattened shape due to the canceling of the noise. The difference between the blade and handle is referred to as variance loss.
Anyway check them out if you’re interested.