The record
of observed temperature at Amos, Quebec, shows how changes in sites and their
surrounding environment can affect the estimation of long-term changes in the
climate. Between 1927 and 1963, the Stevenson screen at the Amos station was
located at the bottom of a hill (see Figure 4.2a) and was moved after 1963 (see
Figure 4.2b) to level ground several metres away from its original place. The
site was sheltered by trees and a building between 1927 and 1963, which could
have prevented the cold air from draining freely during nighttime. The current
site has an open exposure and is more representative of its surrounding region.
Careful comparison of the temperature data at this site with those at a nearby
station revealed two step-changes, one of −0.8ºC in 1927 and another of 1.3ºC
in 1963 (see Figure 4.2c). The station history files do not provide information
on the cause of the first step, but it is possible that the screen was also
relocated at that time. These differences resulted in the original temperature
data showing an increasing trend of 2.4ºC for 1951–1995 (see Figure 4.2d),
whereas, after the artifact in temperature reading was removed, a warming of
only 0.8ºC was shown
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