9860 W. Saanich Rd. Analyses of temperatures from boreholes in previously forested areas in western Canada disclose sudden increases of one to two degrees in ground surface temperature at the times of deforestation at each site. A warming of the ground surface over a large area of Central Canada, synchronous with the deforestation of southern Ontario and neighboring regions in the nineteenth century, may be an example of climate change linked to the widespread creation of agricultural lands. A 227-year record shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska. The recent warming exceeds that of prior centuries, extending back to A.D. 1600.
Results illustrate two features of general interest.
First, a city with constant population still shows a temperature trend due to changes in urban morphology and energy consumption. This means that regional data sets including urban records may have a bias associated with temperature trends, as well as a bias due to urban growth. For the U.S. during 1901-1984, the two types of bias could be of the same order but opposite sign. Simulations with a land surface process model coupled to an atmosphere general circulation model show that the climate of the U.S. with modern vegetation is significantly different from that with natural vegetation. The climate change caused by land use practices is comparable to other anthropogenic climate forcings.