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).


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.