Read here. For the paleo-climate scientists associated with the IPCC and Climategate, it was critical that they disavow the existence of the Medieval Warming and the Little Ice Age. Thus, the result was the original "Hockey Stick" chart fabrication, as well as additional paleo hockey stick studies. By removing the Medieval warming from IPCC charts, they hoped to prove that the current warming was unique over the last 2,000 years. Unfortunately for the Climategate "scientists," the paleo record keeps producing undeniable evidence, like below. (click on image to enlarge)
"Not wanting to acknowledge that the earth was likely as warm as, or even warmer than, it is currently a thousand or so years ago (when the atmosphere's CO2 concentration was much lower than it is today), the world's climate alarmists have been loath to admit there was an MWP or Medieval Warm Period anywhere other than in countries surrounding the North Atlantic Ocean. Consequently, the seven independent speleothem records that produced the results reported by Lorrey et al. are of great importance to the ongoing global warming debate, as they greatly advance the thesis that the MWP was indeed a global phenomenon."
Other climate history postings. Other historical temperature charts. Modern temperature charts.