The fact is that the uptick in temperature at the end of the reconstruction period is a real feature of the proxy data used in this study. (tamino.wordpress.com)
There also may be systematic errors in the use of these proxies which I will get to in a minute. (climate-skeptic.com)
In recent decades, a number of groups have tried combining sets of these proxy records together to construct long - term estimates of global temperature change over the last millennium or so. (globalwarmingsolved.com)