Climate, the average weather conditions over a period of at least thirty years, is determined by various factors, the most important of which are the amount of precipitation and the temperature of the air. Climate controls the major ecological community types, or biomes; that is, the climate in a given region determines the flora and fauna that will thrive in that region. In 1900, Wladimir Koppen, a German climatologist, developed what has become the most widely used system for classifying world climates. The Koppen system identifies five major climate zones: tropical moist climates (A zone), dry climates (B zone), humid middle latitude climates (C zone), continental climates (D zone), and cold climates (E zone). Koppen also used two subgroups to more specifically describe the zones.

Tropical moist climates are characterized by year-round high temperatures and large amounts of rain. Rainfall is adequate all year round, and there is no dry season. This zone is typical of northern parts of South America, central Africa, Malaysia, Indonesia, and Papua New Guinea. The dry climate zone has little rain and a wide range of daily temperatures. There is a dry season in the summer and winter, with a mean annual temperature over or under 18œ Celsius, as in the western United States, northern and extreme southern Africa, parts of central Asia, and most of Australia.

The humid middle latitude climate, or temperate zone, has hot-to-warm, dry summers and cool, wet winters, but no dry season as such. Southeastern sections of the United States and South America, westernmost Europe, and the southeast corner of China fit this category. The continental climate zone, in interior regions of large land masses such as Canada and northern Europe and Asia, experience varied seasonal temperatures and moderate rainfall. The cold climate zone, characterized by permanent ice and ever-present tundra, occupies Greenland and the most northerly parts of Asia.

While acknowledging some unknowns and uncertainty, researchers predicts that, if global warming caused by carbon dioxide (CO2) and other greenhouse gas (GHG) emissions continue at the current rate, some of the climate zones recognized in the early twenty-first century could disappear entirely by the end of the century, giving way to new climate zones on up to 39 percent of the world's land surface. Major areas that could be affected are tropical highlands and polar regions. Broad strips of areas labeled tropics and subtropics at the beginning of the twenty-first century could develop new climates that do not resemble any of the zones in categories assigned in the Koppen Climate Classification System. Researchers predict that heavily populated areas such as the southeastern United States, southeastern Asia, parts of Africa such as its mountain ranges, the Amazonian rain forest, and South American mountain ranges are likely to be the most severely affected.

Climate change patterns could affect ecosystems on a global scale. For example, major changes in the forests of North America could result: Four species of tree--the yellow birch, the sugar maple, the hemlock, and the beech--are expected to move northward up to 1,000 kilometers while abandoning entirely their present-day locations. Animals could also be affected. Temperature and rainfall patterns could change breeding and migration patterns.

For humans, a grave concern is global food production. One model predicts that the corn belt in North America will move northward, possibly as far as Canada; winter wheat may replace corn in parts of the present corn belt. Within several decades, the Swiss Alps could become a Mediterranean climate, with wet winters and long, dry, warm summers. Within one hundred years, the climate zone in southern Switzerland may move northward by as much as 500 kilometers. In the western Alps, the climate may come to resemble that found in southern France in the early twenty-first century.

Biodiversity in South Africa is expected to be affected substantially by shifting climate zones: Species will experience extinction on a wide scale; up to half the country will see a climate not known before; succulent karoo, a globally important arid-climate hotspot, and biomes in the fynbos (a Mediterranean-climate thicket) will suffer. While the degree of this change remains speculative, availability of food could affect sub-Saharan West Africa, as vegetation zones move southward.

Deforestation will continue in the Amazonian forest areas of South America, and new climates are expected to be created near the equator. Some researchers predict that mountainous areas such as those found in Peru and the Colombian Andes, as well as regions in Siberia and southern Australia, could experience the disappearance of climates completely. Devastation of critical ecosystems and changes in agricultural patterns could severely affect Australia, New Zealand, and the developing island nations of the Pacific. With so many factors still undetermined or speculative, however, it remains to be seen how climate zone changes will play out in the future.

References:

1)         Burroughs, William James. Climate Change: A Multidisciplinary Approach. 2d ed. New York: Cambridge University Press, 2007.

2)         Diaz, Henry F., and Richard J. Murnane, eds. Climate Extremes and Society. New York: Cambridge University Press, 2008.

3)         Ennis, Christine A., and Nancy H. Marcus. Biological Consequences of Global Climate Change. Sausalito, Calif.: University Science Books, 1996.

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