Reference:Mann and Jones 2003
From Global Warming Art[ Mann, M.E. and P.D. Jones (2003). "Global Surface Temperatures over the Past Two Millennia". Geophysical Research Letters 30 (15): 1820. DOI:10.1029/2003GL017814.
"We present reconstructions of Northern and Southern Hemisphere mean surface temperature over the past two millennia based on high-resolution 'proxy' temperature data which retain millennial-scale variability. These reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the Northern Hemisphere. Conclusions for the Southern Hemisphere and global mean temperature are limited by the sparseness of available proxy data in the Southern Hemisphere at present."
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