claim: it later emerged that its creator Dr Michael Mann had spliced too [ sic ] datasets together – tree-rings showing temperatures going back hundreds of years, then recent thermometer readings for the more recent decades.
evidence: Mann said, Ten years ago, the availability of data became quite sparse by the time you got back to 1,000 AD, and what we had then was weighted towards tree-ring data; but now you can go back 1,300 years without using tree-ring data at all and still get a verifiable conclusion.