Climate and the climate system
Climate refers to the long-term patterns of atmospheric conditions and weather phenomena in a specific area, typically assessed over a thirty-year period. It encompasses key variables such as temperature, precipitation, humidity, winds, and the occurrence of extreme weather events. Climate classification can be achieved through empirical methods, which focus on the observable effects of climate, or genetic methods that examine its underlying causes. Two main classification systems exist: the Köppen system, which categorizes climate based on temperature and precipitation alongside vegetation types, and the Bergeron system, which emphasizes the characteristics of air masses based on moisture and temperature.
The climate system is a complex interplay of five major components: the atmosphere, hydrosphere, cryosphere, land surface, and biosphere. These elements interact through various physical, chemical, and biological processes, influencing global climate patterns. For example, the atmosphere is where most weather events occur, while the oceans play a crucial role in regulating climate due to their thermal properties. The interactions among these components contribute to vital cycles such as the hydrologic and carbon cycles, which are essential for maintaining climate stability. Changes within any part of the climate system can trigger feedback mechanisms, leading to further climate shifts, underscoring the intricate balance and sensitivity of this system.
Subject Terms
Climate and the climate system
Definition
Climate is an aggregation of near-surface atmospheric conditions and weather phenomena over an extended period in a given area. It is characterized by statistical means and such variables as air temperature, precipitation, winds, humidity, and frequency of weather extremes. The time period is typically thirty years, as described by the World Meteorological Organization (WMO).
World climate is classified by either the empirical method, focusing on the effects of climate, or the genetic method, emphasizing the causes of climate. The empirical Köppen system, based on annual mean temperature and precipitation combined with vegetation distribution, divides world climate into five groups: tropical, dry, temperate, continental, and polar. Each group contains subgroups, depending on moisture and geographical location.
The genetic Bergeron, or air-mass, classification system is more widely accepted among atmospheric scientists, as it directly relates to climate formation and origin. Air-mass classification uses two fundamental attributes—moisture and thermal properties of air masses. Air masses are classified into dry continental (C) or moist maritime (M) categories. A second letter is assigned to each mass to describe the thermal characteristic of its source region: P for polar, T for tropical, and (less widely used) A for Arctic or Antarctic. For example, the dry cold CP air mass originates from a continental polar region. Sometimes, a third letter is used to indicate the air mass being cold (K) or warm (W) relative to the underlying surface, implying its vertical stability.
Climate System
In a broad sense, climate often refers to an intricate system consisting of five major components: the atmosphere, hydrosphere, cryosphere, land surface (a portion of the lithosphere), and biosphere, all of which are influenced by various external forces such as Earth-Sun orbit variations and human activities. The atmosphere, where weather events occur and most climate variables are measured, is the most unstable and rapidly changing part of the system. The Earth’s atmosphere is composed of 99 percent permanent gases (nitrogen and oxygen) and 1 percent trace gases, such as and water vapor. All weather and climate phenomena are associated with the trace gases called greenhouse gases (GHG). Long-term increases in GHG concentration warm the climate, while day-to-day variations in atmospheric thermal and dynamic structures are responsible for daily weather events.
The hydrosphere comprises all fresh and saline waters. Freshwater runoff from land returning to the ocean influences the ocean’s composition and circulation, while transporting a large amount of chemicals and energy. Because of their great thermal inertia and huge moisture source, oceans regulate the Earth’s climate. The cryosphere consists of those parts of the Earth’s surface covered by permanent ice in polar regions, alpine snow, sea ice, and permafrost. It has a high reflectivity (albedo), reflecting solar radiation back into space, and is critical in driving deep-ocean circulation.
Land surfaces and the terrestrial biosphere control how energy received at the surface from the Sun is returned to the atmosphere, in terms of heat and moisture. The partitioning between heating and moistening the atmosphere has profound implications for the initiation and maintenance of convection and thus for precipitation and temperature. Marine and terrestrial biospheres have major impacts on the atmosphere’s composition through the uptake and release of GHG during and organic material decomposition.
Interactions Among Climate System Components
The individual components of the climate system are linked by physical, chemical, and biological interactions over a wide range of space and time scales. The atmosphere and oceans are strongly coupled by moisture and heat exchange. This coupling is responsible for El Niño, the North Atlantic Oscillation, and the Pacific Decadal Oscillation, resulting in climate swings on interannual to interdecadal scales. The terrestrial and atmosphere exchange gases and energy through transpiration, photosynthesis, and radiation reflection, absorption, and emission.
These interactions form the global water, energy, and carbon cycles. The hydrologic cycle leads to clouds, precipitation, and runoff, redistributing water among climate components. Oceans and land surfaces absorb solar radiation and release it into the atmosphere by diffusion and convection. Global carbon and other gas cycles are completed by photosynthesis fixing CO2 from the atmosphere and depositing it into the biosphere, soil, and oceans as organic materials, which are then decomposed by microorganisms and released back into the atmosphere.
Any change or disturbance to the climate system can lead to chain reactions that may reinforce or suppress initial perturbation through interactive feedbacks. If the climate warms, melting of glaciers and will accelerate, and the surface will absorb more solar radiation, further enhancing warming. On the other hand, warmer air temperatures result in more moisture in the atmosphere, increasing cloud cover, which increases and reduces the absorbed solar radiation. This leads to cooling, compensating for the initial warming. There exist many such positive and negative feedback mechanisms, which makes the causality of climate change complex.
Bibliography
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Bridgman, Howard A., and John E. Oliver. The Global Climate System: Patterns, Processes, and Teleconnections. New York: Cambridge University Press, 2006.
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McKnight, Tom L., and Darrel Hess. Physical Geography: A Landscape Appreciation. 9th ed. Upper Saddle River, N.J.: Prentice Hall, 2008.
Oliver, John E., and John J. Hidore. Climatology: An Atmospheric Science. 2d ed. Upper Saddle River, N.J.: Prentice Hall, 2002.
Regoto, Clara, et al. "What Do We Mean by 'Climate' and 'Climate Change'?" Frontiers, 28 Mar. 2022, kids.frontiersin.org/articles/10.3389/frym.2022.671886. Accessed 13 Dec. 2024.