But the graph was questioned by sceptics who pointed out that is it impossible to know for certain the global temperature going back beyond modern times because there were no accurate readings.
The issue became a central argument in the climate change debate and was dragged into the 'climategate' scandal, as the sceptics accused Prof Mann and his supporters of exaggerating the extent of global warming.
However, speaking to the BBC recently, Prof Mann, a climatologist at Pennsylvania State University, said he had always made clear there were "uncertainties" in his work.
"I always thought it was somewhat misplaced to make it a central icon of the climate change debate," he said.
Really? I never heard him say it.