Well, no-one has said what I wanted to say about this, so I thought I should. Click on the image for P3′s take. This is about Shaun A. Marcott, Jeremy D. Shakun, Peter U. Clark, Alan C. Mix‘s latest in Science. If you want to read some stupid things said about it, try Curry (surprise) or if you prefer your stupidity super-sized, then WUWT. And indeed, if you want to read drivel, why bother with watered down gruel?
The abstract has something for everyone:
Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time. Here we provide a broader perspective by reconstructing regional and global temperature anomalies for the past 11,300 years from 73 globally distributed records. Early Holocene (10,000 to 5000 years ago) warmth is followed by ~0.7°C cooling through the middle to late Holocene (<5000 years ago), culminating in the coolest temperatures of the Holocene during the Little Ice Age, about 200 years ago. This cooling is largely associated with ~2°C change in the North Atlantic. Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history. Intergovernmental Panel on Climate Change model projections for 2100 exceed the full distribution of Holocene temperature under all plausible greenhouse gas emission scenarios.
If you’re the GWPF, then your headline is Earth cooler today than 28% of the past 11,300 years. If you’re Timmy getting climate wrong as usual, its What Excellent News: Earth Warmer Than in Most of the Past 11,300 Years. I’d probably go with RC’s take What If from 2005. But I’ll continue anyway.
The first thing that strikes me is that the error estimates look insanely tight, and constant. In fact they aren’t really error estimates, I think they are The gray shading [50% Jackknife (Jack50)] represents the 1s envelope when randomly leaving 50% of the records out during each Monte Carlo mean calculation. however I think people are inevitably going to interpret them as error estimates. And yet they don’t include sampling bias or any systematic problems with the datasets.
The second is the sparsity of sites, compared to Mann et al. I’d also whinge about the latitudinal bias of the the sites, too, except as the figure shows that also applies to Mann et al. too.
Point three would be caution in using figure S3, as EW does. That’s not all the records stacked together, as it rather looks like at first (it would be astonishing if it were, far far too tight; compare this).
I’d also read Michael Mann’s comments in Andy Revkin’s piece, in conjunction with pondering figure 2 I/J/K. Is the warmth biased by Northern high latitudes? I don’t know.
That wasn’t a terribly insightful analysis, was it? Well, its early days yet. That was mostly what I wanted to say: don’t over-interpret this picture or paper. I’m sure there’s a lot of more informed comment to come.
I cannot leave you without presenting what may become one of my favourite oh-dear-the-poor-darlings comments, from WUWT of course:
Although a list of sources of the data from the 73 sites is provided in an appendix, nowhere is any real data presented, so assessing the validity or accuracy of the original data is not possible without digging out all of the source papers.
If you need that interpreted, you’re lost, so I won’t try.