Climatology (fromGreekκλίμα,klima, "slope"; and-λογία,-logia) orclimate science is the scientific study of Earth'sclimate, typically defined as weather conditions averaged over a period of at least 30 years.[1] Climate concerns the atmospheric condition during an extended to indefinite period of time; weather is the condition of the atmosphere during a relative brief period of time. The main topics of research are the study ofclimate variability,mechanisms of climate changes andmodern climate change.[2][3] This topic of study is regarded as part of theatmospheric sciences and a subdivision ofphysical geography, which is one of theEarth sciences. Climatology includes some aspects ofoceanography andbiogeochemistry.
The Greeks began the formal study of climate; in fact, the word "climate" is derived from the Greek wordklima, meaning "slope", referring to the slope or inclination of the Earth's axis. Arguably the most influential classic text concerning climate wasOn Airs, Water and Places[4] written byHippocrates about 400BCE. This work commented on the effect of climate on human health and cultural differences between Asia and Europe.[4] This idea that climate controls which populations excel depending on their climate, orclimatic determinism, remained influential throughout history.[4] Chinese scientistShen Kuo (1031–1095) inferred that climates naturally shifted over an enormous span of time, after observingpetrifiedbamboos found underground near Yanzhou (modernYan'an,Shaanxi province), a dry-climate area unsuitable at that time for the growth of bamboo.[5]
During the early 20th century, climatology mostly emphasized the description of regional climates. This descriptive climatology was mainly an applied science, giving farmers and other interested people statistics about what the normal weather was and how great chances were of extreme events.[7] To do this, climatologists had to define aclimate normal, or an average of weather andweather extremes over a period of typically 30 years.[8] While scientists knew of past climate change such as theice ages, the concept of climate as changing only very gradually was useful for descriptive climatology. This started to change during the decades that followed, and while thehistory of climate change science started earlier, climate change only became one of the main topics of study for climatologists during the 1970s and afterward.[9]
Map of the average temperature over 30 years. Data sets formed from the long-term average of historical weather parameters are sometimes called a "climatology".
Various subtopics of climatology study different aspects of climate. There are different categorizations of the sub-topics of climatology. TheAmerican Meteorological Society for instance identifies descriptive climatology, scientific climatology and applied climatology as the three subcategories of climatology, a categorization based on the complexity and the purpose of the research.[10] Applied climatologists apply their expertise to different industries such asmanufacturing andagriculture.[11]
Paleoclimatology is the attempt to reconstruct and understand past climates by examining records such asice cores andtree rings (dendroclimatology).Paleotempestology uses these same records to help determine hurricane frequency over millennia.Historical climatology is the study of climate as related to human history and is thus concerned mainly with the last few thousand years.
Boundary-layer climatology concerns exchanges in water, energy and momentum near surfaces.[12] Further identified subtopics are physical climatology, dynamic climatology,tornado climatology, regional climatology,bioclimatology, andsynoptic climatology. The study of thehydrological cycle over long time scales is sometimes termed hydroclimatology, in particular when studying the effects of climate change on the water cycle.[10]
The study of contemporary climates incorporates meteorological data accumulated over many years, such as records of rainfall, temperature and atmospheric composition. Knowledge of the atmosphere and its dynamics is also embodied inmodels, eitherstatistical ormathematical, which help by integrating different observations and testing how well they match. Modeling is used for understanding past, present and potential future climates.
Climate research is made difficult by the large scale, long time periods, and complex processes which govern climate. Climate is governed by physical principles which can be expressed asdifferential equations. These equations are coupled and nonlinear, so that approximate solutions are obtained by using numerical methods to createglobal climate models. Climate is sometimes modeled as astochastic process but this is generally accepted as an approximation to processes that are otherwise too complicated to analyze.
The collection of a long record of climate variables is essential for the study of climate. Climatology deals with the aggregate data that meteorologists have recorded.[13] Scientists use both direct and indirect observations of the climate, fromEarth observing satellites and scientific instrumentation such as a global network ofthermometers, toprehistoric ice extracted fromglaciers.[14] As measuring technology changes over time, records of data often cannot be compared directly. As cities are generally warmer than the areas surrounding,urbanization has made it necessary to constantly correct data for thisurban heat island effect.[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 of the average temperature of the Earth. Most climate models include the radiative effects ofgreenhouse gases such ascarbon dioxide. These models predict a trend of increase ofsurface temperatures, as well as a more rapid increase of temperature at higher latitudes.
Models can range from relatively simple to complex:
A simple radiant heat transfer model that treats the Earth as a single point and averages outgoing energy.
This can be expanded vertically (radiative-convective models), or horizontally.
Coupled atmosphere–ocean–sea iceglobal climate models discretise and solve the full equations for mass and energy transfer and radiant exchange.
Earth system models further include the biosphere.
Additionally, they are available with different resolutions ranging from >100 km to 1 km. High resolutions in global climate models are computational very demanding and only few global datasets exists. Examples are ICON[16] or mechanistically downscaled data such as CHELSA (Climatologies at high resolution for the Earth's land surface areas).[17][18]
Various factors affect the average state of the atmosphere at a particular location. For instance, midlatitudes will have a pronouncedseasonal cycle of temperature whereastropical regions show little variation of temperature over a year.[20] Another major variable of climate is continentality: the distance to major water bodies such asoceans. Oceans act as a moderating factor, so that land close to it has typically less difference of temperature betweenwinter and summer than areas further from it.[21] The atmosphere interacts with other parts of theclimate system, with winds generatingocean currents that transport heat around the globe.[22]
Classification is an important method of simplifying complicated processes. Differentclimate classifications have been developed over the centuries, with the first ones inAncient Greece. How climates are classified depends on what the application is. Awind energy producer will require different information (wind) in a classification than someone more interested in agriculture, for whom precipitation and temperature are more important.[23] The most widely used classification, theKöppen climate classification, was developed during the late nineteenth century and is based on vegetation. It uses monthly data concerning temperature andprecipitation.[24]
There are different types of variability: recurring patterns of temperature or other climate variables. They are quantified with different indices. Much in the way theDow Jones Industrial Average, which is based on the stock prices of 30 companies, is used to represent the fluctuations of stock prices in general, climate indices are used to represent the essential elements of climate. Climate indices are generally devised with the twin objectives of simplicity and completeness, and each index typically represents the status and timing of the climate factor it represents. By their very nature, indices are simple, and combine many details into a generalized, overall description of the atmosphere or ocean which can be used to characterize the factors which effect the global climate system.
El Niño–Southern Oscillation (ENSO) is a coupled ocean-atmosphere phenomenon in the Pacific Ocean responsible for much of the global variability of temperature,[22] and has a cycle between two and seven years.[25] TheNorth Atlantic oscillation is a mode of variability that is mainly contained to the lower atmosphere, thetroposphere. The layer of atmosphere above, thestratosphere is also capable of creating its own variability, most importantly theMadden–Julian oscillation (MJO), which has a cycle of approximately 30 to 60 days. TheInterdecadal Pacific oscillation can create changes in the Pacific Ocean and lower atmosphere on decadal time scales.
Climate change occurs when changes of Earth'sclimate system result in newweather patterns that remain for an extended period of time. This duration of time can be as brief as a few decades to as long as millions of years. The climate system receives nearly all of its energy from the sun. The climate system also gives off energy toouter space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determinesEarth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.[26] Climate change also influences the averagesea level.
In contrast tometeorology, which emphasises short termweather systems lasting no more than a few weeks, climatology studies the frequency and trends of those systems. It studies the periodicity of weather events over years to millennia, as well as changes of long-term average weather patterns in relation to atmospheric conditions.Climatologists study both the nature of climates – local, regional or global – and the natural or human-induced factors that cause climates to change. Climatology considers the past and can helppredict futureclimate change.
A relative difficult method of forecast, the analog technique requires remembering a previous weather event which is expected to be mimicked by an upcoming event. What makes it a difficult technique is that there is rarely a perfect analog for an event of the future.[28] Some refer to this type of forecasting as pattern recognition, which remains a useful method of estimating rainfall over data voids such as oceans using knowledge of how satellite imagery relates to precipitation rates over land,[29] as well as the forecasting of precipitation amounts and distribution of the future. A variation of this theme, used for medium range forecasting, is known asteleconnections, when systems in other locations are used to help determine the location of a system within the regime surrounding.[30] One method of using teleconnections are by using climate indices such as ENSO-related phenomena.[31]
^Weart, Spencer (2008)."Climatology as a Profession".history.aip.org. American Institute of Physics.Archived from the original on 9 May 2020. Retrieved25 October 2019.
^Dipankar, A.; Heinze, Rieke; Moseley, Christopher; Stevens, Bjorn; Zängl, Günther; Brdar, Slavko (2015). "A Large Eddy Simulation Version of ICON (ICOsahedral Nonhydrostatic): Model Description and Validation".Journal of Advances in Modeling Earth Systems.7.
Jenny Uglow, "What the Weather Is" (review of Sarah Dry,Waters of the World: The Story of the Scientists Who Unraveled the Mysteries of Our Oceans, Atmosphere, and Ice Sheets and Made the Planet Whole, University of Chicago Press, 2019, 332 pp.),The New York Review of Books, vol. LXVI, no. 20 (19 December 2019), pp. 56–58.
KNMI Climate Explorer The Royal Netherlands Meteorological Institute's Climate Explorer graphs climatological relationships of spatial and temporal data.
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