Physical effects common to all freshwater ecosystems
TEMPERATURE CHANGES
There is widespread consensus that the greenhouse effect will lead to a global rise in air
temperature, with mean surface temperatures increasing 1.5 to 5.8_ C by the year 2100
(Houghton et al., 2001). Temperatures are expected to increase more at higher latitudes,
and in many of these regions the effects of global warming have already been documented;
in Canada, mean air temperatures, water temperatures, and evaporation have all
increased in the past 20-30 years (Schindler, 2001), and ice cover durations over lakes
and rivers have decreased over the entire northern hemisphere by almost 20 days since
the mid-1800’s (Magnuson et al., 2000).