http://www.americanthinker.com/2013/08/a_tale_of_two_climate_hockeysticks.html
The false “hockeystick” graph with which (in 2001) the UN climate panel claimed that current surface temperatures are “unprecedented” in a millennium is at odds with hundreds of scientific papers and with their own previous position. There is nothing unusual about today’s temperatures; the world was warmer in the Middle Ages. However, the “hockeystick” graph showing a rapid increase in 20th century CO2 concentration is genuine.
The Third Assessment Report (2001) of the UN-sponsored IPCC (Intergovernmental Panel on Climate Change) espouses a temperature history over the last thousand years that resembles a ‘hockeystick’ (HS). The ‘shank’ is the smooth decline of temperature from 1000 to 1900AD, followed by an apparent sharp rise in the 20th century (forming the ‘blade’ of a hockeystick). IPCC-AR3 promoted this rise as definitive evidence of human influence on climate; emission of carbon dioxide was supposed to cause the 20th century warming. But this temperature history is fake; it is contradicted by much other evidence.