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Climate is the long-term weather pattern in a region, typically averaged over 30 years.[1][2] More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorological variables that are commonly measured are temperature, humidity, atmospheric pressure, wind, and precipitation. In a broader sense, climate is the state of the components of the climate system, including the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere and the interactions between them.[1] The climate of a location is affected by its latitude, longitude, terrain, altitude, land use and nearby water bodies and their currents.[3]

Climates can be

biological diversity and how climate change affects it. The major classifications in Thornthwaite’s climate classification are microthermal, mesothermal, and megathermal.[5]

Finally, the Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.

global warming, which results in redistributions of biota. For example, as climate scientist Lesley Ann Hughes has written: "a 3 °C [5 °F] change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km [190–250 mi] in latitude (in the temperate zone) or 500 m [1,600 ft] in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones."[7][8]


Climate (from

Ancient Greek κλίμα 'inclination') is commonly defined as the weather averaged over a long period.[9] The standard averaging period is 30 years,[10] 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) 2001
glossary definition is as follows:

Climate in a narrow sense is usually defined as the "average weather", or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.[11]


climate normals" as "reference points used by climatologists to compare current climatological trends to that of the past or what is considered typical. A climate normal is defined as the arithmetic average of a climate element (e.g. temperature) over a 30-year period. A 30-year period is used as it is long enough to filter out any interannual variation or anomalies such as El Niño–Southern Oscillation, but also short enough to be able to show longer climatic trends."[12]

The WMO originated from the International Meteorological Organization which set up a technical commission for climatology in 1929. At its 1934 Wiesbaden meeting, the technical commission designated the thirty-year period from 1901 to 1930 as the reference time frame for climatological standard normals. In 1982, the WMO agreed to update climate normals, and these were subsequently completed on the basis of climate data from 1 January 1961 to 31 December 1990.[13] The 1961–1990 climate normals serve as the baseline reference period. The next set of climate normals to be published by WMO is from 1991 to 2010.[14] Aside from collecting from the most common atmospheric variables (air temperature, pressure, precipitation and wind), other variables such as humidity, visibility, cloud amount, solar radiation, soil temperature, pan evaporation rate, days with thunder and days with hail are also collected to measure change in climate conditions.[15]

The difference between climate and weather is usefully summarized by the popular phrase "Climate is what you expect, weather is what you get."

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.[19][20]

Climate classification

Map of world dividing climate zones, largely influenced by latitude. The zones, going from the equator upward (and downward) are Tropical, Dry, Moderate, Continental and Polar. There are subzones within these zones.
Worldwide Köppen climate classifications

Climate classifications are systems that categorize the world's climates. A climate classification may correlate closely with a biome classification, as climate is a major influence on life in a region. One of the most used is the Köppen climate classification scheme first developed in 1899.[21]

There are several ways to classify climates into similar regimes. Originally,

classification schemes
is that they produce distinct boundaries between the zones they define, rather than the gradual transition of climate properties more common in nature.



Paleoclimatology is the study of past climate over a great period of the Earth's history. It uses evidence with different time scales (from decades to millennia) from ice sheets, tree rings, sediments, pollen, coral, and rocks to determine the past state of the climate. It demonstrates periods of stability and periods of change and can indicate whether changes follow patterns such as regular cycles.[24]


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 over the modern time scale, their observation frequency, 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.[25] Long-term modern climate records skew towards population centres and affluent countries.[26] Since the 1960s, the launch of satellites allow records to be gathered on a global scale, including areas with little to no human presence, such as the Arctic region and oceans.

Climate variability

Climate variability is the term to describe variations in the mean state and other characteristics of climate (such as chances or possibility of extreme weather, etc.) "on all spatial and temporal scales beyond that of individual weather events."[27] Some of the variability does not appear to be caused systematically and occurs at random times. Such variability is called random variability or noise. On the other hand, periodic variability occurs relatively regularly and in distinct modes of variability or climate patterns.[28]

There are close correlations between Earth's climate oscillations and astronomical factors (

climate proxy data, positive feedback processes or anthropogenic emissions of substances such as greenhouse gases.[29]

Over the years, the definitions of climate variability and the related term climate change have shifted. While the term climate change now implies change that is both long-term and of human causation, in the 1960s the word climate change was used for what we now describe as climate variability, that is, climatic inconsistencies and anomalies.[28]

Climate change

Average surface air temperatures from 2011 to 2021 compared to the 1956–1976 average. Source: NASA
Observed temperature from NASA[30] vs the 1850–1900 average used by the IPCC as a pre-industrial baseline.[31] The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability.[32]

Climate change is the variation in global or regional climates over time.[33] It reflects 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.[34][35] In recent usage, especially in the context of

Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations.[36]

Earth has undergone periodic climate shifts in the past, including four major ice ages. These consist 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 period. Suggested causes of ice age periods include the positions of the continents, variations in the Earth's orbit, changes in the solar output, and volcanism.[37] However, these naturally-caused changes in climate occur on a much slower time scale than the present rate of change which is caused by the emission of greenhouse gases by human activities.[38]

Climate models

atmosphere,[39] oceans
, land surface and ice through a series of physics equations. They are used for a variety of purposes; from the 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 imbalance results in a change in the average temperature of the earth.

Climate models are available on different resolutions ranging from >100 km to 1 km. High resolutions in

global climate models require significant computational resources, and so only a few global datasets exist. Global climate models can be dynamically or statistically downscaled to regional climate models to analyze impacts of climate change on a local scale. Examples are ICON[40] or mechanistically downscaled data such as CHELSA (Climatologies at high resolution for the earth's land surface areas).[41][42]

The most talked-about applications of these models in recent years have been their use to infer the consequences of increasing greenhouse gases in the atmosphere, primarily

global mean surface temperature
, with the most rapid increase in temperature being projected for the higher latitudes of the Northern Hemisphere.

Models can range from relatively simple to quite complex. Simple radiant heat transfer models treat the earth as a single point and average outgoing energy. This can be expanded vertically (as in radiative-convective models), or horizontally. Finally, more complex (coupled) atmosphere–ocean–

global climate models discretise and solve the full equations for mass and energy transfer and radiant exchange.[43]

See also


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  2. ^ Shepherd, J. Marshall; Shindell, Drew; O'Carroll, Cynthia M. (1 February 2005). "What's the Difference Between Weather and Climate?". NASA. Archived from the original on 22 September 2020. Retrieved 13 November 2015.
  3. ISSN 2674-0494
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  5. ^ "All About Climate". Retrieved 2023-09-25.
  6. ^ "paleoclimatology | science | Britannica". Archived from the original on 2022-09-01. Retrieved 2022-09-01.
  7. ^ Hughes, Lesley (2000). Biological consequences of globalwarming: is the signal already. p. 56.
  8. from the original on 12 October 2013. Retrieved November 17, 2016.
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  10. ^ "Climate averages". Met Office. Archived from the original on 2008-07-06. Retrieved 2008-05-17.
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  14. ^ "WMO Climatological Normals". World Meteorological Organization. Archived from the original on 2022-08-21. Retrieved 2022-08-21.
  15. from the original on 2022-08-08. Retrieved 2022-08-20.
  16. ^ National Weather Service Office Tucson, Arizona. Main page. Archived 2017-03-12 at the Wayback Machine Retrieved on 2007-06-01.
  17. ^ Rahmstorf, Stefan. "The Thermohaline Ocean Circulation: A Brief Fact Sheet". Potsdam Institute for Climate Impact Research. Archived from the original on 2013-03-27. Retrieved 2008-05-02.
  18. ^ de Werk, Gertjan; Mulder, Karel (2007). "Heat Absorption Cooling For Sustainable Air Conditioning of Households" (PDF). Sustainable Urban Areas Rotterdam. Archived from the original (PDF) on 2008-05-27. Retrieved 2008-05-02.
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  28. ^ a b Rohli & Vega 2018, p. 274.
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  35. ^ Gillis, Justin (28 November 2015). "Short Answers to Hard Questions About Climate Change". The New York Times. Archived from the original on 22 September 2020. Retrieved 29 November 2015.
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Further reading

External links

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