World Climate Zones

Climate is the average weather of a place over a long period, usually thirty years, while weather is the condition of the atmosphere at a particular time. Climate zones are broad bands defined mainly by temperature and rainfall, which in turn depend on latitude, altitude, distance from the sea, ocean currents and prevailing winds. The simplest division is into tropical, temperate and polar zones, separated by the Tropics of Cancer and Capricorn and the Arctic and Antarctic Circles, but geographers use finer classifications, the best known being that of Wladimir Köppen, which divides climates by temperature, precipitation and vegetation.

The equatorial climate, found near the equator in the Amazon, Congo basin and South-East Asia, is hot and wet all year, with heavy convectional rainfall almost daily and dense evergreen rainforest. The tropical monsoon climate, found in South and South-East Asia, has a sharp wet and dry season driven by seasonal wind reversal. The hot desert climate, found in the Sahara, Arabia, the Thar and the Australian outback, has very low rainfall and large daily temperature ranges, because dry air and clear skies allow rapid heating by day and cooling by night. The Mediterranean climate, found around the Mediterranean Sea and in California, Chile, South Africa and south-west Australia, has wet winters and dry summers, suiting olives, grapes and citrus fruit.

Temperate climates, in the mid-latitudes, have four distinct seasons and moderate rainfall, supporting deciduous forests, grasslands and intensive farming. Continental climates in the interiors of large landmasses have hot summers and very cold winters, because land heats and cools faster than sea. Polar and tundra climates, near the poles and on high mountains, are cold year-round, with frozen ground and only brief growing seasons. Altitude creates similar changes: climbing a mountain is like travelling towards the poles, with temperature falling as height increases.

For civil studies, climate zones explain where people live, what they grow, and what risks they face. They explain why rice suits monsoon Asia, wheat suits temperate plains, and pastoralism suits dry grasslands; why some regions face drought, others flood, and others cold; and why climate change does not affect all places equally. A warming world shifts zones, expands deserts, melts ice and changes rainfall, so the map of climate zones is not fixed. Policy on agriculture, water, migration and disaster preparedness must therefore read climate as a moving pattern, not a permanent label.