Unlike what we’ve seen previously in climate science, where it takes years of complaints, demands, taunts, FOI’s and other assorted embarrassments to finally pry code and data out of scientists, McShane and Wyner made all their data and code available up front. That allowed R coder mind of a Markov chain to replicate portions of the M&W work.

They write:

There are a bunch of “hockey sticks” that calculate past global temps. through the use of proxies when instrumental data is absent. There is a new one out there by McShane and Wyner (2010) that’s creating quite a stir in the blogosphere (here, here, here, here). The main take out being, that the uncertainty is too great for the proxies to be any good.

Here’s an output from the replication:

They continue:

I think this is pretty much identical to Fig. 18b in the paper. One thing to notice is that I smoothed over the estimates and the 95% intervals. M&W2010 weirdly draws over all instances of the simulations (notice the wide grey intervals). Since all the realizations of the model are overlapping each other, the graph effectively shows the maximum and minimum of the 95% interval. Where my interval will probably be interpreted as about +/- 0.4 on each side, M&W2010′s paper could be interpreted as +/- 0.5 degrees. This is a large difference especially for a paper that espouses large uncertainties in the proxy data. OTOH, Mann et al. (2008) I think produces mean uncertainty bounds which might be confusing depending on one’s perspective. Apparently there is another paper (w/ code and data) coming out soon that uses Bayesian hierarchical models that I might recreate as well (Bo Li1, Douglas W. Nychka2 and Caspar M. Ammann. 2010. The Value of Multi-proxy Reconstruction of Past Climate). More fun to chew on.

Read the entire essay here

h/t to WUWT reader Uppyn

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