Lee has criticized me for not fully canvassing the supposedly manifold lines of evidence marshalled by the NAS panel against a warmer MWP. So I’ve done a little exercise to summarize the evidence AGAINST the MWP being warmer than mid-20th century, disaggregating what I believe to be the salient information from the spaghetti studies. The information is familiar, but it’s arranged below a little differently than I normally arrange it.
In my opinion, there’s a fair bit of evidence the other way – some examples mentioned here from time to time include: Cuffey’s Greenland reconstruction/Dahl-Jensen’s Greenland boreholes; Naurzbaev in Siberia, Millar et al in California, Law Dome dO18 isotopes in Antarctica, Pollissar on glaciers in the Venezuelan Alps, higher treelines in Scandinavia, Lamb’s European evidence; the Polar Urals update, … But that’s not what we’re here for today.
So let’s turn the question around – what is the evidence AGAINST a warmer MWP?
(1) bristlecone and foxtail ring widths (especially those collected by Graybill in the 1980s) are wider in modern times than in medieval times. (OK, the NAS panel has discounted this, but it’s obviously been used over and over as evidence against a warmer MWP in the spaghetti studies.)
(2) ring widths at Yamal, adjusted for age, are wider than in modern times than in medieval times;
(3) the percentage of coldwater diatoms offshore Oman is higher in the 20th century than in MWP;
(4) dO18 levels in some of Thompson’s tropical ice cores and in the overall average is higher than modern levels;
(5) combinations of the above 4 proxies under a weighted average with small numbers of other mostly nondescript proxies show mid-20th century indices slightly higher than the highest corresponding index in the MWP (the spaghetti graphs);
(6) supposedly some evidence from Antarctica according to the NAS Panel, but they did not provide any evidence and I don’t know what it is;
(7) 5000-year organics from Quelccaya (Thompson 2006, cited by NAS panel)
I realize that my arrangement of 1-5 is based on a POV, but have I left anything out from the NAS panel? I haven’t posted anything on (7) yet, but intend to do so. I’ve written extensively on items 1-5; I’ve got a note up on point 6 inviting a response, but nobody has so far volunteered a guess on what the NAS panel, those sturdy engineers and bridge designers, had in mind.
If the parties were in civil litigation or other proceeding to be decided on balance of probabilities, one would weigh the evidence from treelines, crops etc, on the one hand against the evidence listed in points (1-7) or any others to be added to this list. The case for the Team is far from overwhelming expressed like this.