Like the dollar, "unprecedented" just doesn't go as far as it used to.
Believers in anthropogenic global warming argue that current warming is unprecedented. The gist of my counter-argument is that numerous studies show warming was greater during the Medieval Warm Period (800 to 1300AD), and that it was even warmer during the Holocene Climate Optimum 9,000 to 5,000 years ago. These studies will show that warming during those periods was global and persistent, was reflected in ice cores, lake and ocean sediments, in the distribution of plants by latitude and elevations, and evidence from human settlements and historical records.
Arrayed against this record of natural climate changes going back over 11,000 years to the end of the Ice Age, the alleged evidence of man-caused global warming spans 60 years when global temperatures both rose and fell while atmospheric carbon dioxide increased. Now the “Climategate” e-mails show that alarmist scientists had to “hide the decline,” admit that the Medieval Warm Period was as warm or warmer, and that it is a “travesty” that their computer models can’t explain recent cooling.