The field of paleoclimatology includes ancient temperature records. (en.wikipedia.org)
Paul Nurse (voice over): Tree rings have been shown to be a good way of measuring ancient temperatures, and they've mostly matched instrumental measurements since the advent of thermometers. (wattsupwiththat.com)
Comparing these records with ancient temperature reconstructions, the researchers found that warm - blooded animals had much greater success at expanding their ranges and adapting to new climate conditions. (scientificamerican.com)