Climate

Climate is the pattern and variation of weather conditions in a given place over a long period. It is customary to use a 30-year period to distinguish long-term patterns from short-term fluctuations. Key measurements include temperature, precipitation, humidity, wind, and atmospheric pressure.

Climate and weather are not the same. Weather is the condition at a given hour or day: rain, sun, or wind. Climate is the recurring pattern of those conditions measured over many years. Therefore a single cold day does not change the climate of a region.

Factors that determine climate

First, the amount of solar radiation reaching a place depends on latitude. Areas near the equator receive more direct sunlight, which brings more heat. Also important are land elevation (mountainous areas are cooler), distance from the sea, the flow of warm and cold ocean currents, and patterns of global wind circulation. Mountains deflect wind, which causes rain on one side and drought on the other (rain shadow).

Climate classifications

The most widely used system for classifying climates is the Köppen system, based on temperature, precipitation, and vegetation type. It divides climates into broad categories: tropical wet, arid and semi-arid, temperate, continental, and polar. Somalia and much of East Africa fall within arid and semi-arid zones, where rainfall comes in specific seasons.

Climate change

Climate changes over long periods. Natural causes include variations in Earth's orbit, volcanic eruptions, and fluctuations in solar output. However, the warming observed in recent centuries is largely attributed to increased atmospheric greenhouse gases (carbon dioxide, methane) from fossil fuel combustion and changes in land use. Reported consequences include rising global temperature, rising sea levels, and shifts in rainfall patterns.

Methods of measurement

Climate data are gathered from weather stations, ocean vessels, satellites, and weather balloons. For periods before modern records, scientists rely on physical evidence: ice cores, tree rings, and ocean sediment layers. Computer models are used to simulate how the climate system responds to various changes.