Abstract: Abstract   Climategate, which happened before 2009 UN Climate Change Conference at Copenhagen, have sharply intensified the debate within the scientific community on the so-called ''hockey stick'' reconstruction of temperature variations over the last millennium. In this paper, a brief summary of the development of the debate is made and special attention is given to two key issues, namely, whether the Medieval Warm Period and the Little Ice Age existed on a global scale, and whether the 20th century was the warmest one in the last millennium. It's found that along with the uncertainties of large-scale temperature reconstructions being increasingly reduced with the update of proxy dataset and improvements of reconstruction methods during the last 20 years, a general consensus among scientists on the issues is beginning to emerge. Particularly, several latest large-scale temperature reconstructions showed that the 20th century warmth, no matter in amplitude or rate, was not unprecedented in the last millennium.

Key words: last two millennia, temperature variation, reconstruction, uncertainty