I wanted to put this figure into my previous post on Marcott et al (2013), but the article was already too long. I think it's the best of the lot. It was probably a bit too complex for mainstream media so hasn't been given much attention.
Take your time to digest it. The authors have tried to fit a lot into the one diagram and there are lots of stories in it. See how the distribution has now shifted to the right, for example. Look how far it's shifted between 1900 to 2000 - in just 100 years!
It's not the "once upon a time long, long ago" part that is a concern. That's fascinating in its own right. It's the future story that is truly worrisome.
Look at the scenarios to see what could happen if we don't begin to sharply cut CO2 emissions this decade. Heck, its bad enough even if we could get CO2 back to the 2000 level. (Click on the diagram for larger version.)
The emissions scenarios (B1...A1F1) are taken from the IPCC AR4 Working Group 1 report (same scenarios as for TAR), and are described in this IPCC Special Report.
We've been promised a discussion of Markott et al on RealClimate.org. Worth watching out for.