Euan
Like you I have always been impressed by our being 3000 feet below the arctic - the difference between a world record wheat yield (Haddington, E Lothian) and no arable farming is less than ~1000 ft in our part of Europe.
Thanks for the charts. To me they reinforce the message of just how sensitive climate is to persistent relatively very small forcing. We know that already of course, because of cycling between glacial and interglacial. I have also long been interested in biological reinforcement of these climate cycles - the advance or retreat of boreal forests affect on northern hemisphere albedo being a case in point. It seems reasonable to me prima facie to separate out from (e.g. Mann et al) and compare the study of temperature series represented by biological proxies with other signals of past temperature. The variation then seen in your charts is very interesting, and indicates boundaries of uncertainty. (It does occur to me that biological proxies might cycle for unknown reasons with cosmic background.)
Although arctic summer sea ice retreated a record amount as recently as 2007 (comparison with 2008 at http://www.nsidc.org/arcticseaicenews/ ) I would agree that it is too early to tell whether the trend to extreme summer melt will be maintained over the next decade or so.
Phil