Revista Chilena de Historia Natural 77 (3): 439-453, 2004
RESEARCH ARTICLE
Potential effects of climate change on the temperate zones of North and South
America
Under current conditions, large areas of temperate western North America and temperate
southern South America have arid to subhumid climates that make them vulnerable to changes as a result of human-induced climate
change. Predictions of climate change from global circulation models with a doubling of present atmospheric levels of
CO<sub>2</sub> suggest large changes in mean annual temperature and small to no changes in mean annual precipitation
and the proportion of precipitation received during the summer. Our objective here was to evaluate how predictions of climate change
from global circulation models will influence climatic patterns and by inference the distribution of temperate zone ecosystems in North
and South America. Calculations of annual water deficits suggest that the area affected by very dry conditions will double as a result of
climate change. This expansion will take place in the vicinity of the currently dry areas. Monthly water deficit calculations suggest that
approximately half of the temperate zone on each continent is affected by at least one month of deficit. Under a doubled
CO<sub>2</sub> climate, these areas would expand to cover up to 77 % of the temperate zone of North America and up to
80 % of South America. The resulting changes to the current distribution of ecosystems will likely be an expansion of deserts at the
expense of grasslands in North and South America and an expansion of grasslands at the expense of deciduous and boreal forest in
North America. Our analyses assumed that future climatic changes will be encompassed by the predictions of our three doubled
CO<sub>2</sub> scenarios. The most likely situation is that actual changes, if they occur, will be different from our
scenarios. Therefore, our analyses should be interpreted as indications of the sensitivity of portions of the North and South American
temperate zones to increases in temperature. The key conclusion from our analyses is that any increase in temperature caused by
climate change will result in expansion of the driest portions of both continents.
Key words:
climate change,
temperate ecosystems, global circulation model, CO<sub>2</sub>
