This information was published in 2013 and involves hard data obtained from ice core analysis. (legalinsurrection.com)
Ice core analysis by Dansgaard's group, confirmed by the Americans, showed rapid oscillations of temperature repeatedly at irregular intervals throughout the last glacial period. (history.aip.org)
We rely on ice core analysis to discover temperature trends of the past millennia because there was no reliable measurement system prior to 1714 when Daniel Fahrenheit invented the first mercury - in - glass thermometer. (thenewamerican.com)