Climate and the climate system
Definition (Encyclopedia of Global Warming)
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....
(The entire section is 237 words.)
Climate System (Encyclopedia of Global Warming)
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 carbon dioxide (CO2) 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 circulations, 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...
(The entire section is 299 words.)
Interactions Among Climate System Components (Encyclopedia of Global Warming)
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 biosphere 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 sea ice will accelerate, and the surface will absorb more solar radiation, further...
(The entire section is 258 words.)
Further Reading (Encyclopedia of Global Warming)
Ahrens, Donald C. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 9th ed. Belmont, Calif.: Brooks/Cole, 2009. Textbook with many colorful illustrations of how climate and weather systems work. The last two chapters present concise summaries of the climate system and changes.
Bridgman, Howard A., and John E. Oliver. The Global Climate System: Patterns, Processes, and Teleconnections. New York: Cambridge University Press, 2006. Covers regional climate anomalies, global teleconnections, recent climate change, and human impacts upon the climate system.
Hartmann, Dennis L. Global Physical Climatology. San Diego, Calif.: Academic Press, 1994. Rigorous presentation of the physical principles that govern the energetics and gas exchanges within the climate system; focuses on the atmosphere.
McKnight, Tom L., and Darrel Hess. Physical Geography: A Landscape Appreciation. 9th ed. Upper Saddle River, N.J.: Prentice Hall, 2008. Covers all five components of the climate system; chapter 8 is devoted to climatic zones and types.
Oliver, John E., and John J. Hidore. Climatology: An Atmospheric Science. 2d ed. Upper Saddle River, N.J.: Prentice Hall, 2002. A descriptive textbook mainly for nonscientists who have a basic working understanding of the climate system.
(The entire section is 184 words.)