Deep borehole temperature profiles have been analyzed to determine ground temperature histories in central and eastern Canada. Clear signs of a cold period between 1500 and 1800 A.D., corresponding to the little ice age, have been found. A warming trend after 1800 A.D. was detected throughout eastern and central Canada. Temperature profiles from western Ontario are consistent and were inverted simultaneously to yield a regional ground temperature history. The recent warming appears to be correlated with the increase of atmospheric CO2 reported for a Greenland ice core. ¿ American Geophysical Union 1992