The Earth's Climate

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Climates and biomes

The climate of a region is defined by the average values and variations of its meteorological data. The distribution of living organisms in a given zone is determined primarily by its temperature and precipitation (rain, hail or snow).
Temperatures on Earth vary according to the location, season, and time of day. They can range from -80 degrees Celsius in the depth of the Antarctic winter to +60 degrees Celsius in certain desert zones at midday in the summer. The distribution of average annual temperatures on the continents' surface divides the globe into five main zones: a warm zone located between the two Tropics, two frigid zones around the poles and two temperate zones in between.
Rainfall is essentially governed by atmospheric circulation. Desert regions are associated with zones of downward atmospheric motion, near the Tropics, and with the very cold zones near the poles. Rainy regions are associated with zones of upward atmospheric motion, located around the Equator and in the low-pressure zones of the middle latitudes. Rainfall averages 2 meters per year at the Equator, 70 centimeters in the semi-arid zones of the Tropical latitudes, 1 centimeter in the Subtropical deserts, and 1 meter in the middle latitudes.
The climate map shows the temperature and rainfall zones associated with the different latitudes: in red for the warm and humid Equatorial zone, yellow for the arid zones, green for the temperate zones and blue for the frigid zones.
Knowing the arrangement of these major climatic zones makes it easier to understand the distribution of living organisms in biomes.
A biome is a set of ecosystems characteristic of a biogeographic area, named for its predominant plant and animal species. For simplification purposes 11 major biomes can be defined.
The polar cap regions of Greenland and the Antarctic are a sterile desert in which no life can be sustained.
The tundra only exists in the circumpolar regions. It hosts a modest flora of moors, grasses, mosses and lichens, and a fauna that, albeit not highly diversified, is well adapted to the extreme climatic conditions.
In the taiga, or subarctic boreal forest, the flora consists primarily of conifers, which can withstand the frigid climate. This is the northernmost wooded zone on the planet.
The temperate forest, or mixed forest, is made up mostly of deciduous trees. The specific tree species are determined by the climate, which can be oceanic, continental or mixed. Found in Europe, Asia and North America, this type of biome accommodates an abundant and highly varied fauna.
The prairie, which includes the steppes of Asia, the pampas of Argentina and the South African Veld, is characterized by the profuse growth of annual herbaceous plants.
The chaparral biome is found around the Mediterranean and in regions with comparable climates in California, Chile, South Africa and southern Australia. The vegetation is adapted to a climate that is warm and dry in the summer and mild in winter.
The desert is an arid region with almost no flora or fauna. Depending on its altitude and latitude, a desert can be very hot or very cold. The savanna is found in tropical climates that alternate between a rainy season and a shorter dry season. This biome consists of tall grasses, interspersed more or less densely with trees or shrubs.
The tropical rainforest, or equatorial forest, is typical of the intertropical Torrid Zone. It is characterized by tall trees and a profusion of plant and animal species. Today, all of the planet's equatorial rainforests are threatened by deforestation.
The temperate rainforest is characteristic of temperate regions with heavy precipitation. Its flora consists largely of conifers or deciduous trees. This biome can be found in the North West of the United States as well as in southwestern Canada, southern Chile, Tasmania and New Zealand.
The mountain biome is actually a set of biomes that differ according to altitude rather than latitude. Deciduous trees in the lower zones give way to conifers and then to alpine tundra, while the peaks are snow-capped or rocky deserts.
These different environments influence the presence, activities and lifestyles of a large proportion of humankind. The deserts, high plateaux and subarctic regions where living conditions are particularly harsh have very low densities of population. In contrast, the temperate zones are very hospitable to human populations. The regions near the oceans are also increasingly populated, even though they are exposed to the significant climatic risk of repeated natural disasters.