Most scientists now agree that the Earth is hotter than it has been for at least a thousand years.
Reconstructions of the fossil record, and more recently from tree rings and ice cores, are giving some tantalising clues about the Earth's more distant past. Tales of Norse seafarers settling on Greenland have led many to believe that there was a Medieval warm period - but this has turned out to be a myth. It was certainly warmer than now 6,000 years ago, with much of Northern Europe basking in temperatures 2 degrees or so higher than now. In addition, scientists are certain that this natural warming several millennia ago does not explain the temperature rise of today. Changes in the Earth's orbit also explain why temperatures in the 'Penultimate Interglacial Period' about 125,000 years ago were higher than today.