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For other uses, see Climate (disambiguation).
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Climate is the average and variations of weather in a region over long periods of time. Climate zones can be defined using parameters such as temperature and rainfall. Paleoclimatology focuses on ancient climate information derived from sediment found in lake beds, ice cores, as well as various fauna and flora including tree rings and coral. Climate models can be used to determine the amount of climate change anticipated in the future.
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Annual average surface temperatures from 1961-1990. This is an example of how climate varies with location.
Climate, (from Ancient Greek klima) is commonly defined as the weather averaged over a long period of time.Glossary of Meteorology. Climate. Retrieved on 2008-03-09. The standard averaging period is 30 years,MetOffice. Climate Averages. Retrieved on 2008-03-09. but other periods may be used depending on the purpose. Climate also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. The Intergovernmental Panel on Climate Change (IPCC) glossary definition is:
The main difference between climate and everyday weather is best summarized by the popular phrase "Climate is what you expect, weather is what you get."National Weather Service Office Tucson, Arizona. Main page. Retrieved on 2007-06-01. Over historic time spans there are a number of static variables that determine climate, including: latitude, altitude, proportion of land to water, and proximity to oceans and mountains. Other climate determinants are more dynamic: The thermohaline circulation of the ocean distributes heat energy between the equatorial and polar regions; other ocean currents do the same between land and water on a more regional scale. Degree of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming or global cooling. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least insofar as the determinants of historical climate change are concerned.
There are a couple different ways climate zones are defined. They can be defined by plant hardiness,United States National Arboretum. USDA Plant Hardiness Zone Map. Retrieved on 2008-03-09. or more generally under the Köppen climate classification.
A grassland biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes. Grasslands are dominated by grass and other herbaceous plants. Savannas are grasslands with scattered trees. Shrublands are dominated by woody or herbaceous shrubs.
Rainfall in tropical and subtropical grasslands, savannas, and shrublands is between 300 and 1500 millimeters (20 to 60 inches) a year[citation needed] , and can be highly seasonal, with the entire year\'s rainfall sometimes occurring within a couple of weeks. Much of the plant life on savannas is adapted to seasonal aridity. Adaptations to the dry climate include herbaceous annuals, which die in the dry season and re-grow from seed each year, and perennial plants which grow long tap roots to reach groundwater, or bulbs to store water.
Tropical and subtropical grasslands, savannas, and shrublands occur on all continents but Antarctica. They are widespread on Africa, and are also found in India, the northern parts of South America and Australia, and the southern United States.
A climate zone characterized by hot, humid summers and chilly to mild winters. This climate type covers a broad category of climates, and the term "subtropical" may be a misnomer for the winter climate in the cooler areas within this category. Significant amounts of precipitation occur in all seasons in most areas. Winter rainfall (and sometimes snowfall) is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and an occasional tropical storm, hurricane or cyclone.
Humid subtropical climates lie on the southeast side of all continents except Antarctica, roughly between latitudes 25° and 40° north and south. The only exceptions where this climate zone reaches up to latitude 46° North, are the Po Valley and the Toulouse regions in Europe. The Köppen definition of this climate is for the coldest month to be above 0 °C mean (Köppen: C), and the warmest month to be above 22 °C (Köppen: a); and to be constantly moist with the driest month to get more than 60 mm rain (Köppen: f).The Times Atlas of the World (1993). Times Books ISBN 0-7230-0492-7.
Details of the modern climate record are known through the taking of measurements from such weather instruments as thermometers, barometers, and anemometers during the past few centuries. The instruments used to study weather conditions over the modern time scale, their known error, their immediate environment, and their exposure have changed over the years, which must be considered when studying the climate of centuries past.Spencer Weart. The Modern Temperature Trend. Retrieved on 2007-06-01.
Paleoclimatology is the study of climate change taken on a long scale, spanning a greater section of the Earth\'s history. It uses records from ice sheets, tree rings, sediment, coral, and rocks to determine the past state of the climate system on Earth, and whether or not long term climate cycles exist.National Oceanic and Atmospheric Administration. NOAA Paleoclimatology. Retrieved on 2007-06-01.
Climate change refers to the variation in the Earth\'s global climate or in regional climates over time. It describes changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities.
In recent usage, especially in the context of environmental policy, the term "climate change" often refers only to changes in modern climate, including the rise in average surface temperature known as global warming. In some cases, the term is also used with a presumption of human causation, as in the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations.Climate Change 2001: The Scientific Basis
Earth has undergone periodic climate shifts in the past, including four major ice ages. These consisting of glacial periods where conditions are colder than normal, separated by interglacial periods. The accumulation of snow and ice during a glacial period increases the surface albedo, reflecting more of the Sun\'s energy into space and maintaining a lower atmospheric temperature. Increases in greenhouse gases, such as by volcanic activity, can increase the global temperature and produce an interglacial. Suggested causes of ice age periods include the positions of the continents, variations in the Earth\'s orbit, changes in the solar output, and vulcanism.Illinois State Museum (2002). Ice Ages. Retrieved on 2007-05-15.
Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the weather and climate system to projections of future climate. All climate models balance, or very nearly balance, incoming energy as short wave (including visible) electromagnetic radiation to the earth with outgoing energy as long wave (infrared) electromagnetic radiation from the earth. Any unbalance results in a change in the average temperature of the earth.
The most talked-about models of recent years have been those relating temperature to emissions of carbon dioxide (see greenhouse gas). These models predict an upward trend in the surface temperature record, as well as a more rapid increase in temperature at higher altitudes.
Models can range from relatively simple to quite complex:
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Template:Meteorological variables
| Climate types under the Köppen climate classification | |
|---|---|
| Class A | Equatorial (Af) · Monsoon (Am) · Savanna (Aw, As) |
| Class B | Desert (BWh, BWk) · Semi-arid (BSh, BSk) |
| Class C | Humid subtropical (Cfa, Cwa) · Oceanic (Cfb, Cwb, Cfc) · Mediterranean (Csa, Csb) |
| Class D | Humid continental (Dfa, Dwa, Dfb, Dwb) · Subarctic (Dfc, Dwc, Dfd, Dwd) · Continental (Dsa, Dsb) · Other continental (Dsc, Dsd) |
| Class E | Polar (ET, EF) · Alpine (ET/H) |
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