Sorry, wasn't clear.
I meant the "CO2" charts and now that I check it out, most of the CO2 charts here have been posted by other people.
There is a paper on the long-term sea ice linked from the Scientific American article but it's behind a firewall, and after five minutes of looking at the Supplementary Information document I sank out of sight without a trace.
His methods are the equivalent of ice core data for sea ice extent, and there's a lot riding on them. How do you check something like this? I do know that melting Greenland ice is uncovering thousand-year-old settlements. That's a trout in the milk, too.