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[Middle English climat, from Old French, from Late Latin clima, climat-, from Greek klima, surface of the earth, region.]
noun
A summary of mean weather conditions over a time period, usually based on thirty years of records. Climates are largely determined by location with respect to land- and sea-masses, to large-scale patterns in the general circulation of the atmosphere, latitude, altitude, and to local geographical features.
For more information on climate, visit Britannica.com.
The climate of an area, defined as the aggregate of weather conditions over time, is constructed from monthly, seasonal, and annual averages of weather elements, such as temperature and precipitation, combined with statements about the frequency of extreme events, such as droughts or tornadoes. Historically, climate has had important economic implications for agriculture, transportation, and settlement. Climatology, or the scientific study of climate, dates to the mid-nineteenth century and includes such specialties as applied climatology, climate dynamics, and climate change.
The classical heritage related the climate of an area uniquely to its latitude. Climate, from the Greek klima, meaning "inclination," was originally thought to depend only on the height of the sun above the horizon, modified in part by special local characteristics. Climate and health have also been closely related throughout history. According to the Hippocratic tradition of ancient Greece, a physician should consider the seasons of the year and what effects each of them produces; the location of a city with respect to winds, waters, terrain, and the rising of the sun; and the particulars of the weather. These were keys to diagnosing and treating diseases in a given location.
The Puzzle of the Early American Climate
Because of its seemingly favorable location in latitudes farther south than most European nations, the New World was expected to have a warm, exotic climate. Initially, colonists and their sponsors envisioned a rich harvest of wine, silk, olive oil, sugar, and spices from their investment. In 1588 the colonial promoter Thomas Harriot pointed out that Virginia was located on the same parallel of latitude as many exotic places, including Persia,
China, and Japan in the East and southern Greece, Italy, and Spain in the West. The reality was much different, however. Early settlers in the Americas found the climate harsher and the storms more frequent and more powerful than in the Old World. In 1644 the Reverend John Campanius of Swedes' Fort, Delaware, wrote of violent winds, unknown in Europe, which tore mighty oaks out of the ground. Another colonist in New Sweden, Thomas Campanius Holm, described rainstorms in which the whole sky was filled with smoke and flames. James Mac Sparran, a missionary to Rhode Island between 1721 and 1757, warned against immigrating to America because the climate was unhealthy, with excessive heat and cold, sudden changes of weather, unwholesome air, and terrible thunder and lightning.
Because of such reports, many Europeans held considerable disdain for the New World and for its climate, soil, animals, and indigenous peoples. The noted Parisian naturalist Georges-Louis Leclerc de Buffon speculated that, because of the cool and humid climate, the flora and fauna of the New World were degenerate. The celebrated botanist and traveler Pehr Kalm observed, rightly or not, that every life-form had less stamina in the New World. People died younger, women reached menopause earlier, soldiers lacked the vitality of their English counterparts, and even the imported cattle were smaller. He pointed to climatic influences as the probable cause.
Citizens in colonial and early America were quite defensive about these opinions and argued that clearing the forests, draining the swamps, and cultivating the land would improve the climate by changing the temperature and rainfall patterns. No general agreement, however, emerged about the direction or magnitude of the change. The Reverend Cotton Mather wrote in the Christian Philosopher (1721) that he believed it was getting warmer. Benjamin Franklin agreed, noting that compared to forested lands, cleared land absorbs more heat and melts snow quicker. In his Notes on the State of Virginia (1785), addressed to a European audience, Thomas Jefferson presented an apology for the harsh American climate and an optimistic prognosis for its improvement by human activities. Hugh Williamson of Harvard College spoke for his generation when he wrote in Observations on the Climate in Different Parts of America (1811) that settlement would result in a temperate climate and clear atmosphere that would serve as "a proper nursery of genius, learning, industry and the liberal arts." In his mind such changes added up to a continent better suited to white settlers and less suited to aboriginal inhabitants.
Climate Observations and Medical Meteorology
The first comprehensive series of meteorological observations in America, taken by John Lining, a physician in Charleston, were related to his medical concerns. In 1740, Lining collected the intake and outflow of his own body for a period of one year in an effort to understand how the weather affected bodily humors and epidemic diseases. Related efforts by Lionel Chalmers, An Account of the Weather and Diseases of South Carolina (1776); William Currie, An Historical Account of the Climates and Diseases of the United States of America (1792); and Noah Webster, A Brief History of Epidemic and Pestilential Diseases (1799) linked regional health conditions to climate and extreme weather events.
Jefferson and the Reverend James Madison began the first simultaneous comparative meteorological measurements in America in 1778. As president of the American Philosophical Society, Jefferson collected weather journals from around the county. He also directed the Lewis and Clark expedition (1804–1806) to take weather observations along the Missouri River and in the Pacific Northwest. Jefferson was a strong advocate for a national meteorological system and encouraged the federal government to supply observers in each county of each state with accurate instruments. Although such a system was not established in his lifetime, many government agencies soon began collecting and compiling observations. During the War of 1812, the surgeon general of the army, James Tilton, ordered the physicians under his command to "keep a diary of the weather" and to file detailed reports on the effects of the climate on the health of the troops. This was because more soldiers were falling ill in camp than were being injured in military engagements. The U.S. Army Medical Department continued its system of taking meteorological measurements at army posts across the country until 1874, in part to document potential changes in the climate. Other early governmental systems included the General Land Office (1817–1821), interested primarily in settlement west of the Appalachian Mountains, and academies in the state of New York (1825–1850), where students collected climatic and phenological statistics. In the 1850s, the U.S. Navy compiled wind and weather charts for the oceans under the direction of Matthew Fontaine Maury.
Under the direction of Joseph Henry, the Smithsonian Institution served as a national center to advance and coordinate meteorological research. The institution conducted storm studies, experimented with telegraphic weather prediction, and collected climate statistics. It also served as a clearinghouse for cooperative observations taken by the navy, the army topographical engineers, the Patent Office, the Coast Survey, the Department of Agriculture, and the government of Canada. Projects completed with Smithsonian data included Climatology of the United States (1857) by Lorin Blodget, Winds of the Globe (1875) by James Henry Coffin, and theoretical studies of the general circulation of the Earth's atmosphere by William Ferrel.
In 1858, Ferrel announced a new theory of fluid mechanics that explained both meridional (E-W) and zonal (N-S) wind flows on the rotating Earth. He wrote equations of motion that accounted for most of the observed features of the general circulation: three vertical circulation cells instead of just one traditional "Hadley cell," high-velocity westerly winds in midlatitudes in both hemispheres, easterly trade winds in the tropics, and low pressure with easterly winds near the poles. Later commentators referred to Ferrel's theory as the "principia meteorologica" because of its fundamental implications for subsequent studies of climate dynamics.
In 1870, Congress established the first national weather service and placed it under the auspices of the Army Signal Office. Colonel Albert J. Myer became the first director of a well-funded national storm warning system employing the nation's telegraphy circuits "for the benefit of commerce and agriculture." In addition to providing daily reports of current conditions and "probabilities" for the next day's weather, the Signal Office collected official climate statistics for the nation. By 1891 the U.S. Weather Bureau had been established in the Department of Agriculture, where it remained until 1940, when it was transferred to the Department of Commerce.
Climate Change in the Nineteenth Century
In 1844, Samuel Forry analyzed data gathered from more than sixty army medical officers and concluded (a) climates are stable and no accurate the rmometrical observations warrant the conclusion of climatic change, (b) climates can be changed by human activity, but (c) these effects are extremely subordinate to physical geography. Elias Loomis studied the temperature of New Haven, Connecticut, and Charles A. Schott constructed national maps of temperature and rainfall. Neither scientist found evidence that humans were changing the climate. Cleveland Abbe, the chief scientist with the National Weather Service, agreed that the old debates about climate change had finally been settled. In an article entitled "Is Our Climate Changing?" published in Forum in February 1889, Abbe defined the climate as "the average about which the temporary conditions permanently oscillate; it assumes and implies permanence."
As the debate over climate change caused by human activities was winding down in the mid-nineteenth century, the discovery that the earth had experienced ice ages produced a plethora of complex but highly speculative theories of climatic change involving astronomical, physical, geological, and paleontological factors. The leading American involved in these discoveries was the prominent glacial geologist T. C. Chamberlin, whose interdisciplinary work on the geological agency of the atmosphere and the effect of carbon dioxide on climate led him to propose a new theory of the formation of the earth and the solar system.
Regional Climates and Identities
Many regions of the United States experience distinctive climatic phenomena. New England, the Appalachian Highlands, and the upper Mississippi Valley have rigorous winters with snow covering the ground, often for several months. The East Coast has a relatively mild climate due to the proximity of the Atlantic Ocean, but these areas are susceptible to land-falling Atlantic hurricanes and winter "nor'easters." The Deep South has hot summers and mild winters with high humidity because of the proximity of the warm waters of the Caribbean and the Gulf of Mexico; on average this area has the most thunderstorms. The heartland experiences the most violent tornadoes, while the high Plains have the most hailstorms. Monsoonal flows from Mexico water the desert Southwest, while California is susceptible to drying "Santa Anna" winds that can exacerbate wildfires. As scientists have come to realize, all regions of the country may be affected by the El Niño Southern Oscillation of the Pacific Ocean.
It would be foolish to argue that such climatic differences "determined" social relations in these regions, just as it would be futile to argue that the environment made little or no difference to people's lives. It is more productive to ask how the flux of economic and social activities over time changed human relationships with nature in sometimes subtle but often dramatic ways. Horse-drawn sleighs were traditionally safe, enjoyable, and often productive means of winter transportation, yet the widespread use of the automobile transformed snow from a transportation resource into a hazard. Pioneers facing the onset of winter and the possibility of crop failure due to frosts believed that warmer weather was better weather, while contemporary city dwellers in urban heat islands find the weather unbearably hot. Air conditioning undoubtedly stimulated the growth of the Sun Belt, while access to freshwater resources may determine the region's future. In general, social and technological changes and changes in scientific understanding of climate have occurred at much faster rates than have physical changes in the climate system.
Settlers seeking to relocate west of the Appalachian Mountains usually headed due west. They assumed that the climatic zone they were familiar with followed parallels of latitude. Generally, this is not the case, since agricultural hardiness zones gradually slope from northeast to southwest. Thus, for example, settlers from Connecticut established the Western Reserve in Ohio. Further west across the Mississippi River lay the semiarid, treeless prairies that were originally called the "Great American Desert." While farmers on the northern and eastern margins of this area, where annual rainfall totals twenty inches or more, had considerable success, precipitation decreases dramatically to the south and west, attaining true desert conditions in New Mexico and Arizona. The Homestead Act of 1862 encouraged farmers ever westward into marginal lands that were fertile only when it rained. Promoters even resorted to the dubious argument that agriculture somehow increases rainfall, or "rain follows the plow." A succession of drought years could devastate farms, however, as was the case in the decade-long Dust Bowl of the 1930s in the southern Great Plains.
Climate Change in the Twentieth Century
By 1900 most of the chief theories of climate change had been proposed if not yet fully explored: changes in solar output; changes in the earth's orbital geometry; changes in terrestrial geography, including the form and height of continents and the circulation of the oceans; and changes in atmospheric transparency and composition, in part due to human activities. During the International Geophysical Year (1957–1958), Harry Wexler of the U.S. Weather Bureau succeeded in establishing a series of accurate measurements of carbon dioxide. After 1958 these measurements were accurately and faithfully taken at the summit of Mauna Loa volcano in Hawaii by Charles David Keeling. Subsequently, many more international baseline stations have been established. The Keeling curve, the famous saw-toothed curve of rising carbon dioxide concentrations, became the environmental icon of the twentieth century.
In the 1950s, Gilbert Plass developed a computer model of infrared radiative transfer in support of his re-search on carbondioxide and climate. Several years later, in the interest of national security, a climate model known as Nile Blue was developed by the Advanced Research Projects Administration (ARPA) in the Department of Defense. It was hoped that this model could be used to test the sensitivity of the climate to major perturbations, including Soviet tinkering or a major environmental war. In 1967, Syukuro Manabe and Richard T. Wetherald developed a computerized climate model that included the effects of both radiation and convection to calculate temperature as a function of latitude. It predicted a mean warming of 2.3 degrees Celsius for a doubling of carbon dioxide. Two years later, Manabe and Kirk Bryan added basic oceanic features to the model.
The rise of the environmental movement in the early 1970s generated interest in global environmental problems, including climate change. In 1971, when some meteorologists were looking into the possibility of a widespread global cooling, a report from the Study of Man's Impact on Climate conducted at the Massachusetts Institute of Technology returned the focus to carbon dioxide emissions, calling them the largest single anthropogenic change that may influence the climate in the foreseeable future. During this period, anthropogenic effects on climate were called "inadvertent" climate modification. Several other regional and global pollution issues also emerged in the 1970s, including acid deposition and possible damage to the stratosphere by ozone-depleting chemicals and by the exhaust gases of a fleet of supersonic transport planes.
In the 1980s, scientists debated the possibility of a "nuclear winter" caused by an all-out nuclear exchange. Discovery of depleted levels of ozone over Antarctica in 1985 led to the international Montreal Protocol on Substances that Deplete the Ozone Layer, signed in 1987. In 1988 the scientist James Hansen of the National Aeronautics and Space Administration announced to Congress and the world, "Global warming has begun." He went on to report that, at least to his satisfaction, he had seen the "signal" in the climate noise and that the earth was destined for global warming, perhaps in the form of a runaway greenhouse effect. Hansen later revised his remarks, but his statement remained the starting point of widespread concerns over global warming. That same year the Intergovernmental Panel on Climate Change was formed as a joint program of the United Nations Environmental Program, the World Meteorological Organization, and the International Congress of Scientific Unions. It has a mandate to prepare regular assessments of what is known and what should be done about anthropogenic climate change.
The 1992 United Nations Conference on Environment and Development (the Earth Summit) in Rio de Janeiro produced the Framework Convention on Climate Change (FCCC), which calls for a stabilization of atmospheric carbon dioxide concentrations at a level that would prevent human-induced changes in the global climate. The 1997 Kyoto Protocol, calling for legally binding greenhouse gas emission targets for all developed countries, remained a contentious issue in the early twenty-first century. These conventions and protocols represent geopolitical interventions in the climate system. Many more policies were initiated. Economics also began to play a role, as taxes and incentives were put in place to reduce unwanted emissions. Meanwhile, green social engineers attempted to convince the general public to live sustainably, while "geoengineers" hold in reserve massive technical fixes for the climate system. Notably, health issues related to possible climate change returned as policy issues.
Conclusion
The climate issues that puzzled colonists and early Americans were eventually resolved by government-supported scientists who compiled climate statistics for the continent. Changes in human-climate relations were typically caused not by climate change but by people migrating to new regions or by changes in social relations or technology. Anolder medical geography of "airs, waters, and places" was replaced by the germ theory of disease. Yet as Americans gained control of their microclimatic environments through irrigation, central heating, and air conditioning, they began to lose control of the damage they inflicted on the environment, for example, by excessive burning of fossil fuels. In the second half of the twentieth century, new reasons for climate apprehension emerged in the form of local, regional, and global threats to the atmosphere and to human health. By the dawn of the twenty-first century, the social aspects of the climate had grown to encompass scientific, economic, governmental, and diplomatic initiatives regarding the health and future of the planet.
Bibliography
Fleming, James Rodger. Meteorology in America, 1800–1870. Baltimore: Johns Hopkins University Press, 1990.
———. Historical Perspectives on Climate Change and Culture. New York: Oxford University Press, 1998.
Fleming, James Rodger, ed. Historical Essays on Meteorology, 1919–1995. Boston: American Meteorological Society, 1996.
Kupperman, Karen Ordahl. "The Puzzle of the American Climate in the Early Colonial Period." American Historical Re-view 87 (1982): 1262–1289.
Ludlum, David M. The American Weather Book. Boston: Houghton Mifflin, 1982.
Mergen, Bernard. Snow in America. Washington, D.C.: Smithsonian Institution Press, 1997.
Meyer, William B. Americans and Their Weather. New York: Oxford University Press, 2000.
—James Fleming
There are five climates in Russia. The Polar climate hugs the Arctic coast and yields a 60-day growing season, with July and August averaging temperatures over freezing. Tundra vegetation prevails. South of the tundra, blanketing two-thirds of Russia, is the Subarctic climate with its brief cool summers and harsh cold, mostly dry, winters. With a growing season of sixty to ninety days, the dominant vegetation is taiga (northern coniferous forest), 90 percent of which is underlain by permafrost. In European Russia and Western Siberia, the Subarctic climate merges southward with the Humid Continental Warm-to-Cool Summer climate. Here the winters become less harsh, although much snowier, and the summers become longer and warmer. Growing seasons reach 90 to 120 days, and the vegetation is a temperate mixed forest that joins the broadleaf forests and grasslands to the south. Along the Lower Volga and in the North Caucasus, the climate becomes sub-humid. Here summers become equal to winters, a Semiarid Continental climate prevails, the growing season reaches 120 to 160 days, and grassland, or steppe, vegetation dominates. Particular to Russia's "bread-basket," a terrain with rich black loams, this climate suffers from insufficient precipitation. A tiny strip of Arid Continental climate fringes the Russian shoreline of the Caspian Sea. With hot, dry summers and rather cold, shorter winters, this climate yields a 160- to 200-day growing season. A true desert, it reflects a severe soil-moisture deficit.
Russia's massive landmass, northerly location, and flat-to-rolling terrain dramatically influence these climates. Because three-fourths of Russia is more than 250 miles (400 kilometers) away from a largely frozen sea, the climates are continental, not maritime. Continental climates exhibit wide ranges of temperature (the difference between the warmest and coldest monthly averages) and low average annual precipitation that peaks in summer instead of spring. Climatic harshness increases from west to east as the moderating influence of the warm North Atlantic Ocean decreases. St. Petersburg on the Gulf of Finland has a 45° F (25° C) difference between the July and January mean temperatures and 19 inches (48 centimeters) of annual precipitation. Yakutsk in Eastern Siberia contrasts with a 112° F (65° C) range of temperature and only 4 inches (10 centimeters) of precipitation.
Russia's high-latitude position enhances continentality. Nine-tenths of the country is north of 50° N Latitude. Moscow is in the latitude of Edmonton, Alberta; St. Petersburg equates with Anchorage, Alaska. Russia thus resembles Canada in climate more than it does the United States. High-latitude countries like Russia and Canada suffer low-angle (less-intense) sunlight and short growing seasons that range from 60 days in the Arctic to 200 days along the Caspian shore.
Low relief also augments the negative effects on Russia's climates. Three-fourths of Russia's terrain lies at elevations lower than 1,500 feet (450 meters) above sea level. This further diminishes the opportunities for rain and snow because there is less friction to cause orographic lifting. The country's open western border, uninterrupted except for the low Ural Mountains, permits Atlantic winds and air masses to penetrate as far east as the Yenisey River. In winter, these air masses bring moderation and relatively heavy snow to many parts of the European lowlands and Western Siberia. Meanwhile, a semi-permanent high-pressure cell (the Asiatic Maximum) blankets Eastern Siberia and the Russian Far East. This huge high-pressure ridge forces the Atlantic air to flow northward into the Arctic and southward against the southern mountains. Consequently, little snow or wind affects the Siberian interior in winter. The exceptions are found along the east coast (Kamchatka, the Kurils, and Maritime province).
As the Eurasian continent heats faster in summer than the oceans, the pressure cells shift position: Low pressure dominates the continents and high pressure prevails over the oceans. Moist air masses flow onto the land, bringing summer thunderstorms. The heaviest rains come later in summer from west to east, often occurring in the harvest seasons in Western Siberia. In the Russian Far East, the summer monsoon yields more than 75 percent of the region's average annual precipitation. Pacific typhoons often harry Kamchatka, the Kurils, and Sakhalin Island.
Winter temperatures plunge from west to east. Along Moscow's 55th parallel, average January temperatures fall from a high of 22° F ( - 6° C) in Kaliningrad to 14° F ( - 10° C) in the capital to 7° F ( - 14° C) in Kazan to - 6° F ( - 20° C) in Tomsk. Along the same latitude in the Russian Far East, the temperatures reach low averages of - 29° F ( - 35° C). Northeast Siberia experiences the lowest average winter temperatures outside of Antarctica: - 50° F ( - 45° C), with one-time minima of - 90° F ( - 69° C).
In July, the averages cool with higher latitudes. Thus, the Caspian desert experiences averages of near 80° F (25° C), whereas the Arctic tundra records means of 40° F (5° C). Moscow averages 65° F (19°C) in July.
Bibliography
Borisov, A. A. (1965). Climates of the USSR. Chicago: Aldine Publishing Co.
Lydolph, Paul E. (1977). Climates of the USSR: World Survey of Climatology. Amsterdam: Elsevier.
Mote, Victor L. (1994). An Industrial Atlas of the Soviet Successor States. Houston, TX: Industrial Information Resources.
—VICTOR L. MOTE
Primary Influence on Climate
The major influence governing the climate of a region is its latitude. A broad latitudinal division of the earth's surface into climatic zones based on global winds includes the equatorial zone, or doldrums, characterized by high temperatures with small seasonal and diurnal change and heavy rainfall; the subtropical, including the trade-wind belts and the horse latitudes, a dry region with uniformly mild temperatures and little wind; the intermediate, the region of the prevailing westerlies that, because of several secondary influences, displays wide temperature ranges and marked changeability of weather; and the polar, a region of short summers and long winters, where the ground is generally perpetually frozen (see permafrost). The transitional climate between those of the subtropical and intermediate zones, known as the Mediterranean type, is found in areas bordering the Mediterranean Sea and on the west coasts of continents. It is characterized by mild temperatures with moderate winter rainfall under the influence of the moisture-laden prevailing westerlies and dry summers under the influence of the horse latitudes or the trade winds.
Secondary Influences on Climate
The influence of latitude on climate is modified by one or more secondary influences including position relative to land and water masses, altitude, topography, prevailing winds, ocean currents, and prevalence of cyclonic storms. Climatic types combining the basic factor of latitude with one or more secondary influences include the continental and the marine. Except in the equatorial region, the continental type is marked by dry, sunny weather with low humidity and seasonal extremes in temperature; noteworthy are the Sahara (with the highest temperature on record, 136°F, or 58°C, at Tripoli) and Siberia (with the lowest recorded surface temperature, −93.6°F, or −70°C, at Verkhoyansk). Marine climates are characterized by small annual and diurnal temperature variation and by copious rainfall on the windward side of coastal highlands and mountainous islands; notable is the mean annual precipitation of 451 in. (1146 cm) at Mt. Waialeale, Hawaii.
The coastal, or littoral, climate is one in which the direction of the prevailing winds plays a dominant role—the east coasts having generally the heavier rainfall in the trade-wind belts, the west coasts in westerly belts. Both coasts have a climate resembling the continental during the season when the wind is blowing from the interior of the continent. An instance of the coastal type, in which the precipitation is accentuated by the nearness of a mountain barrier, is the west coast of North America from Alaska to Oregon, where the mean annual precipitation averages 80 to 100 in. (203 to 254 cm), almost all of it falling during the winter months. Elevation is the dominant factor in mountain and plateau climates, with the temperature decreasing about 3°F per 1,000 ft (1.7°C per 305 m) of ascent and rainfall increasing with altitude up to about 6000 ft (1829 m), then decreasing with further elevation.
Climatology and Climatic Change
Climatology, the science of climate and its relation to plant and animal life, is important in many fields, including agriculture, aviation, medicine, botany, zoology, geology, and geography. Changes in climate affect, for example, the plant and animal life of a given area. The presence of coal beds in North America and Europe along with evidence of glaciation in these same areas indicates that they must have experienced alternately warmer and colder climates than they now possess.
Despite yearly fluctuations of climatic elements, there has been, apparently, little overall change during the period of recorded history. Numerous climatic cycles (variations in weather elements that recur with considerable regularity) have been claimed to exist, including an 11-year cycle related to sunspot activity. There is currently much concern that human activities are changing the earth's climate in harmful ways. Computer models of climate changes have been developed in recent years; some examine potential parameters that effect global warming or cooling.
Bibliography
See H. H. Lamb, Climate History and the Future (1985); J. R. Herman and R. A. Sun, Weather and Climate (1985).
Middle Eastern climatic conditions vary greatly, depending on the season and the geography.
The Middle East and North Africa are perceived as both homogeneous and intensely arid, but the region is best characterized by its climatic variation. Although the hot arid, or desert, climate predominates in the region, the well-watered highlands of Turkey and the mountains of Iran and Ethiopia are important as sources of the region's major rivers. Climatic variation finds further expression in the temperature regimes of the northern and southern parts of the area. Average July maxima for inland
locations near 30° north latitude are as high as 108°F (42°C), while summer maximum temperatures in northern locations such as Ankara, Turkey, do not exceed 86°F (30°C). Black Sea coastal stations' (e.g., Trabzon, Turkey) average summer maxima may be as low as 79°F (26°C). January average minimum temperatures fall to 50°F (10°C) in Aswan, but reach 10°F ( - 12.5°C) in Erzurum on the Anatolian plateau.
Desert conditions are primarily the result of the subtropical zone of high pressure that coincides with 30° north latitude. In this area, cold, subsiding air warms as it approaches the earth, thus increasing its ability to hold moisture. This results in extreme evaporation from all surfaces, and under such conditions, very little rain falls. During the summer solstice, the sun is directly overhead at 23° 30′ at north latitude (e.g., at Aswan, Egypt). Annual periods of high sun in combination with clear skies through much of the year allow intense solar radiation with subsequent extreme evapotranspiration demands.
Evapotranspiration refers to the water needed by vegetation to withstand the energy of incoming solar radiation. This is accomplished through the mechanism of heat transfer by means of evaporation from inert surfaces and transpiration from stomata (pores) on leaf surfaces. Total demands made upon an individual plant are termed potential evapotranspiration (PE). Actual evapotranspi-ration (AE) is the amount of water actually available and used by the plant and reflects climatic conditions rather than optimal plant requirements. The difference between PE and AE defines the degree of aridity or drought and also the amount of irrigation water that would have to be applied for such vegetation to survive.
In the deserts of North Africa and Southwest Africa, total annual precipitation is between 2 inches (50 mm) and 14 inches (350 mm). The area from Aden to Baghdad receives from less than 2 inches (50 mm) annually to about 6 inches (150 mm). More than 39 inches (1 m) of water would be required in those places to sustain rain-fed agriculture. Under such conditions, sparse natural vegetation allows animals some seasonal grazing at best. Hyperarid areas, which seldom if ever receive rain, have no vegetation at all. Rainfall variability within the area of desert climate exceeds 40 percent, reducing to 20 percent on the moist margins of the semiarid zone, which forms a transition between the true desert to the south and the more humid areas farther north.
Precipitation on the semiarid margins of Middle Eastern deserts ranges from 14 inches (350 mm) to 30 inches (750 mm) annually. Dry farming of grains employing alternate years of fallow can be carried out with 16 inches (400 mm) or more of rain. It should be remembered that, while rainfall variability is greatest in the desert, this also means that aridity there has high predictability. Thus, the semiarid transition between regions of predictable aridity and predictable rainfall is one where rain-fed agriculture is possible but has a high chance of failure. This is biblical country - years of plenty followed by years of famine - and one to which pastoral nomadism was a practical adaptation.
The Black Sea coast of Turkey receives from 78 inches (2,000 mm) to 101 inches (2,600 mm) per year, although the transition from the windward, watered side of the Pontic range to the leeward, dry side can be very abrupt due to the topography. The Mediterranean climate, which is limited to a narrow coastal strip reaching from Gaza to Istanbul and from Tunis in the west to the Atlantic, is marked by mild winters with ample rain and long, hot summers when Sahara-like conditions prevail.
Precipitation results from three different processes. Orographic precipitation occurs on the Pontic and Taurus mountains of Turkey; the Elburz and Zagros mountains of Iran; the peaks of Lebanon and the hills of Israel, the West Bank, and Jordan; the highlands of Ethiopia; and the Atlas and Anti-Atlas mountains of northwest Africa. Such precipitation occurs as warm, moisture-bearing winds are forced to higher elevations over the mountains. When the air cools, it loses its ability to hold moisture, and rain or snow falls on the wind-ward sides of those ranges.
The Anatolian plateau and the steppes of northern Syria experience small quantities of rain in the form of convectional summer showers from thunderstorms. Equatorial convectional rains provide the waters of the White Nile.
A third cause of precipitation, particularly in the wintertime, is the passage of frontal systems from west to east across the region bringing alternating high and low pressure cells with associated cold, clear, or moist warm air masses. Frontal systems are propelled eastward by the subtropical jet stream, the position of which varies latitudinally by as much as 15° from a winter position in the north to its summer position in the south. Summer months find the path of the jet stream located from central Turkey northeastward to central Asia. Six months later the jet stream is at its maximum along a path traced across the Gulf of Suez to the head of the Gulf of Aqaba and beyond. This shift accounts for the changes in temperature and precipitation noted above.
Surface winds in the Middle East have distinctive qualities and have received local names famous throughout the region. The cold northern wind blowing from the Anatolian plateau to the southern Turkish shore in the winter is the Poyraz (derived from the Greek: bora, i.e., north); the warm on-shore wind in the same location is known as the meltem. Searing desert winds are infamous: The Egyptian khamsin, which blows in from the desert, is matched by the ghibli in Libya and the simoon in Iran.
Bibliography
Beaumont, Peter; Blake, Gerald H.; and Wagstaff, J. Malcolm. The Middle East: A Geographical Study, 2d edition. New York: Halsted Press, 1988.
Blake, Gerald; Dewdney, John; and Mitchell, Jonathan. The Cambridge Atlas of the Middle East and North Africa. Cambridge, U.K., and New York: Cambridge University Press, 1987.
Goudie, Andrew, and Wilkinson, Jon. The Warm Desert Environment. Cambridge, U.K., and New York: Cambridge University Press, 1977.
Grigg, David. The Harsh Lands: A Study in Agricultural Development. London: Macmillan; New York: St. Martin's, 1970.
— JOHN F. KOLARS
A region's usual weather patterns. The climate at any point on Earth is determined by things such as the general movement of the atmosphere, the proximity of the oceans, and the altitude of the location.
The total environmental effect of ambient temperature, barometric pressure, radiation, oxygen concentration, water precipitation, humidity, wind speed, wind direction and sunlight hours or cloud cover. Called also weather.
The climate in Hawaii always seems to be perfect.
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Climate is the average and variations of weather 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.
Climate (from Ancient Greek klima) is commonly defined as the weather averaged over a long period of time. The standard averaging period is 30 years 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."[2] 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
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.[3]
Paleoclimatology is the study of climate change taken on a longer 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.[4]
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.[5]
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.[6]
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:
| Meteorological data and variables |
|---|
| Atmospheric pressure · Baroclinity · Cloud · Convection · CAPE · CIN · Dew point · Heat index · Humidex · Humidity · Lifted index · Lightning · Pot T · Precipitation · Sea surface temperature · Surface solar radiation · Surface weather analysis · Temperature · Theta-e · Visibility · Vorticity · Wind chill · Water vapor · Wind |
| 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) · Mediterranean continental (Dsa, Dsb) . Other continental (Dsc, Dsd) |
| Class E | Polar (ET, EF) · Alpine (ETH) |
| Elements of nature | |
|---|---|
| Earth | History of Earth · Earth science · Structure of the Earth · Plate tectonics · Geological history of Earth · Geology |
| Weather | Climate · Earth's atmosphere |
| Biosphere · Origin of life · Microbe · Plants · Fungus · Fauna · Animals · Biology · Evolutionary history of life | |
| Environment | Wilderness · Ecology · Ecosystem |
| Universe | Matter · Energy · Extraterrestrial life · Outer space |
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Dansk (Danish)
n. - klima, egn, stemning
idioms:
Nederlands (Dutch)
klimaat(gordel), sfeer
Français (French)
n. - climat, (fig) atmosphère, (Écon, Pol) climat
idioms:
idioms:
Ελληνική (Greek)
n. - (μετεωρ.) κλίμα, (μτφ.) ατμόσφαιρα, ιδιάζουσες συνθήκες
idioms:
Italiano (Italian)
clima, atmosfera
idioms:
Português (Portuguese)
n. - clima (m)
idioms:
Русский (Russian)
климат, атмосфера
idioms:
Español (Spanish)
n. - clima, ambiente, atmósfera
idioms:
Svenska (Swedish)
n. - klimat, atmosfär (bildl.)
中文（简体） (Chinese (Simplified))
气候, 思潮, 风土
idioms:
中文（繁體） (Chinese (Traditional))
n. - 氣候, 思潮, 風土
idioms:
