Climate is the weather conditions of a place or region prevailing over a long period of time. The major factors influencing climate are surface and atmospheric temperatures, the movements of air masses in the atmosphere, incoming and outgoing radiation, and the cycle and transportation of moisture both vertically and horizontally.


Climates are defined on different scales, ranging from macroclimates which cover the broad climatic zones of the globe, down to microclimates which refer to the conditions in a small area such as a wood or a field.


Classification of climates

Climates may be classified into groups. The system most used today is that of Vladimir Köppen, with five categories (A, B, C, D, E), broadly defined as follows:


A    Equatorial and tropical rainy climates;
B    Arid climates;
C    Warmer forested (temperate) climates;
D    Colder forested (temperate) climates; and
E    Treeless polar climates.


These categories correspond to a great extent to zoning by latitude; this is because the closer to the equator an area is, the more direct the sunlight it receives and the less the amount of atmosphere through which that sunlight must pass. Other factors are the rotation of the Earth on its axis (diurnal differences) and the revolution of Earth about the Sun (seasonal differences).


Continental climate

A continental climate is a type of climate found in the interior of large continents, that is, hot summers with convectional rainfall and very cold, dry winters, with only light falls of snow. Summer temperatures are about 20°C (68°F), and winter temperatures are -10°C to -20°C (14°F to -4°F) in the coldest month. Total annual precipitation is about 500 mm (20 in). The natural vegetation consists of grassland. Areas of continental climate are found in Poland and Hungary, and on the steppes of Russia, and the prairies of North America. In the Southern Hemisphere there are no areas of real continental climate because the land masses are relatively narrow, so that oceanic influences are present throughout.


Maritime climate

A maritime climate is a climate that is strongly influenced by proximity to the sea. Britain has a maritime climate, which means that it has mild climate for its latitude. Oceans warm up more slowly than land, because the heat of the Sun is spread out through a great depth of water and because ocean currents allow the heat to move vertically as well as horizontally. However, oceans also retain heat for much longer than land. For this reason, climatic conditions near an ocean tend to be much warmer in winter and slightly cooler in summer than in inland areas at the same latitudes. In addition to the effects on temperature, the sea also influences precipitation, which is greater than in inland locations.


The maritime climate in Britain is most marked in the Isles of Scilly, Cornwall, where the average temperature in winter is about 7°C (45°F) – about the same as the Mediterranean coat of France. In the summer, the temperature averages 16°C (61°F), and the total annual rainfall is about 800 mm (32 in). Moving eastwards into Europe, along similar latitudes, the climate gradually changes to a continental climate, such as that in Germany, where the corresponding figures would be about 0°C (32°F), 19°C (66°F), and 550 mm (22 in).


Mediterranean climate

A Mediterranean climate is a type of climate associated with the countries surrounding the Mediterranean Sea, but also found in southern California, central Chile, and parts of Australia. Summers are hot and sunny, averaging 25°C (77°F) or more; winters are mild, ranging from 5°C to 15°C (41°–57°F). Summers are very dry but winters can be quite wet, with up to 600 mm (24 in) of rainfall, some of which come as thunderstorms at the end of the summer.


Branches of climatology

Climatology is the study of Earth's climates. Physical climatology investigates the relationships between temperature, pressure, winds, precipitation, and other weather phenomena. Regional climatology considers latitude and other geographical factors, e.g., the influence of large land masses in the climatic study of a particular place or region.


Climate modeling

Climate modeling is the use of a computer to simulate Earth's climate. Physical data, such as temperature, pressure, wind direction, and so on are manipulated mathematically by a powerful computer to give a model of Earth's whole climatic system. Researchers can vary various parameters to see what changes occur. In this way they can study the effects of the greenhouse effect and global warming, or what would happen if there was a significant change in the amount of radiation from the Sun. Such modeling can be limited by scientists' understanding of the key factors controlling climates.