HAVE you ever wondered why one area of the world is a desert, another a grassland, and another a rainforest? The answer is climate. Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It is the long-term weather of that area (for at least 30 years). This includes the region's general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. The climate of a region will determine what plants will grow there, and what animals will inhabit it.

　　Arctic Climate 寒带气候

　　The main features of this climate are low amounts of precipitation with a summer maximum, mild summers and very cold winters. This extreme climate produces the type of scenery known as the Tundra. The winters in the Tundra as well as being very cold are also very dark. In north of the Arctic circle there are days when the sun does not shine. Precipitation is very low in this season as the cold temperatures reduce evaporation and the air only holds very low amounts of water vapour.

　　Regions with an arctic climate: northern Alaska, northern Canada, coastal areas of Greenland, northern Scandinavia (Norway, Sweden and Finland) and Siberia in northern Russia.

　　Temperate Climate 温带气候

　　Temperate climates are those without extremes of temperature and precipitation. There are two types of temperate climate: maritime and continental.

　　Maritime climates experience generally cool summers and mild winters, with a much smaller annual temperature range. This is because water has a much higher heat capacity than soil and rock. Seawater takes a long time to warm up in summer, but once heated it retains its energy long after the surrounding land has cooled down, helping to moderate the climate.

　　Regions with a maritime climate: Western Europe, in particular the UK, and western North America at latitudes between 40 °and 60°north.

　　Continentality is a measure of the degree to which the climate of a region typifies that of the interior of a large landmass. Such regions usually experience hot summers and cold winters, since they are far away from the moderating influence of the ocean, which keeps climates milder in winter and cooler in summer. This is because soil and rock have a much lower heat capacity than water, and therefore gain and lose heat much more quickly.

　　Regions with a continental climate: Siberia and central Russia, and much of North America.

　　Subtropical Climate 亚热带气候

　　At about 30°north and south of the equator there is a subtropical climate belt of generally dry descending air, associated with high atmospheric pressure and clear skies. Subtropical climates are characterized by hot, humid summers and cool to mild winters. Rainfall is distributed fairly evenly throughout the year. Winter rainfalland sometimes snowfallis associated with large storm systems that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and an occasional tropical storm or hurricane. Humid subtropical climates lie on the southeast side of continents, roughly between 24 degrees and 37 degrees latitude.

　　Regions with a subtropical climate: the southeastern United States, southeastern South America; coastal southeastern South Africa; eastern Australia; Asia from northern India through south China to Japan.

　　Tropical Climate 热带气候

　　Much of the equatorial belt within the tropical climate zone experiences hot and humid weather. There is abundant rainfall due to the active vertical uplift or convection of air found there, and during certain periods, thunderstorms can occur every day. Nevertheless, this belt still receives considerable sunshine, and with the excessive rainfall, provides ideal growing conditions for luxuriant vegetation.

　　The seasons, when they do exist, are distinguished not as warm and cold periods but by variation of rainfall and cloudiness. Greatest rainfall occurs when the midday sun is overhead. On the equator this occurs twice a year, in March and September, and consequently there are two wet and two dry seasons. Farther away from the equator, the two rainy seasons merge into one, and the climate becomes more monsoonal, with one wet season and one dry season. In the Northern Hemisphere, the wet season occurs from May to July, in the Southern Hemisphere, from November to February.

　　Regions with a tropical climate: the Amazon Basin in Brazil, the Congo Basin in West Africa and Indonesia.