Omitting a period because the proxy and instrumental data disagree is not a good thing to do. I think Crowley and Lowery make some weak arguments to justify it, though I'm not convinced by them. But they did omit some data, so we do the same (with some concern). I'm also a little hesitant about being too critical, because one might view our use of a calibration period that ends in 1960 as being a similar thing - we omit the post-1960 period because of the apparent decline in high-latitude tree-ring density!
More Fun With Sea Level
1 hour ago