Cenozoic Tectonics And Climate
Cenozoic global tectonic patterns are dominated by the opening of the Atlantic ocean, closure of the Tethys Ocean and formation of the Alpine-Himalayan Mountain System, and mountain building in western North America. Uplift of mountains and plateaus and the movement of continents severely changed oceanic and atmospheric circulation patterns, altering global climate patterns.
As the North and South Atlantic Oceans opened in the Cretaceous, western North America was experiencing contractional orogenesis. In the Paleocene (66-58 Ma) and Eocene (58-37 Ma), shallow dipping subduction beneath western North America caused uplift and basin formation in the Rocky Mountains, with arc-type volcanism resuming from later Eocene through late Oligocene (about 40-25 Ma). In the Miocene (starting at 24 Ma), the Basin and Range Province formed through crustal extension, and the formerly convergent margin in California was converted into a strike-slip or transform margin, causing the initial formation of the San Andreas fault.
The Cenozoic saw the final breakup of Pangaea and closure of the tropical Tethys Ocean between Eurasia and Africa, Asia, and India and a number of smaller fragments that moved northward from the southern continents. Many fragments of Teth-yan Ocean floor (ophiolites) were thrust upon the continents during the closure of Tethys, including the Semail ophiolite (Oman), Troodos (Cyprus), and many Alpine bodies. Relative convergence between Europe and Africa, and Asia and Arabia plus India continues to this day, and is responsible for the uplift of the Alpine-Himalayan chain of mountains. The uplift of these mountains and the Tibetan Plateau has had important influences on global climate, including changes in the India Ocean monsoon and the cutting off of moisture that previously flowed across southern Asia. Vast deserts such as the Gobi were thus born.
The Tertiary began with generally warm climates, and nearly half of the world's oil deposits formed at this time. By the mid-Tertiary (35 Ma) the Earth began cooling again, and this culminated in the ice house climate of the Pleistocene, with many glacial advances and retreats. The Atlantic Ocean continued to open during the Tertiary, which helped lower global temperatures. The Pleistocene experienced many fluctuations between warm and cold climates, called glacial and interglacial stages (the Earth is currently in the midst of an interglacial stage). These fluctuations are rapid—for instance, in the past 1.5 million years the Earth has experienced 10 major and 40 minor periods of glaciation and interglaciation. The most recent glacial period peaked 18,000 years ago, when huge ice sheets covered most of Canada and the northern United States, and much of Europe.
The human species developed during the Holo-cene Epoch (since 10,000 years ago). The Holocene is just part of an extended interglacial period in the planet's current ice house event, raising important questions about how humans will survive if climate suddenly changes back to a glacial period. Since 18,000 years ago the climate has warmed by several degrees, sea level has risen 500 feet (150 m), and atmospheric C02 has increased. Some of the global warming is human induced. one scenario of climate evolution is that global temperatures will rise, causing some of the planet's ice caps to melt, raising the global sea level. This higher sea level may increase the Earth's reflectance of solar energy, suddenly plunging the planet into an ice house event and a new glacial advance.
See also climate; climate change; mass extinctions; plate tectonics.
Pomerol, Charles. The Cenozoic Era: Tertiary and Quaternary. Chichester, U.K.: Ellis Horwood, 1982. Proterero, Donald, and Robert Dott. Evolution of the
Earth, 6th ed. New York: McGraw Hill, 2002. Stanley, Steven M. Earth and Life through Time. New
York: Freeman, 1986.
climate Climate refers to the average weather of a place or area and its variability over a period of years. The term climate is derived from the Greek work klima, meaning inclination and referring specifically to the angle of inclination of the Sun's rays, a function of latitude. The average temperature, precipitation, cloudiness, and windiness of an area determine its climate. Factors that influence climate include latitude; proximity to oceans or other large bodies of water that could moderate the climate; topography, which influences prevailing winds and may block precipitation; and altitude. All of these factors are linked together in the climate system of any region on the Earth. The global climate is influenced by many additional factors. The rotation of the Earth and latitudinal position determine where a place is located with respect to global atmospheric and oceanic circulation currents. Chemical interactions between seawater and magma significantly change the amount of carbon dioxide in the oceans and atmosphere and may change global temperatures. Pollution from humans also changes the amount of greenhouse gases in the atmosphere, which may be contributing to global warming. Climatology is the field of science concerned with climate, including both present-day and ancient climates. Cli-matologists study a variety of problems, ranging from the classification and effects of present-day climates through to the study of ancient rocks to determine ancient climates and their relationship to plate tectonics. An especially important field actively studied by climatologists is global climate change, with many studies focused on the effects that human activities have had and will continue to have on global climate. Many of these models require powerful supercomputers and computer models known as global circulation models. These models input various parameters at thousands or millions of grid points on a model Earth, and demonstrate how changing one or more variables (e.g., carbon dioxide, or C02, emissions) will affect the others.
Classifications of climate must account for the average, extremes, and frequencies of the different meteorological elements. of the many different ways to classify climate, the most modern classifications are based on the early work of the German clima-tologist Wladimir Koppen. His classification (initially published in 1900) was based on the types of vegetation in an area, assuming that vegetation tended to reflect the average and extreme meteorological changes in an area. He divided the planet into different zones such as deserts, tropics, rain forest, tundra, and the like. In 1928 Norwegian meteorologist Tor Bergeron modified Koppen's classification to include the types of air masses that move through an area and how they influence vegetation patterns. The British meteorologist George Hadley made another fundamental understanding of the factors that influence global climate in the 18 th century. Hadley proposed a simple, convective type of circulation in the atmosphere where heating by the Sun causes the air to rise near the equator and move poleward, where the air sinks back to the near surface, then returns to the equatorial regions. We now recognize a slightly more complex situation, in that there are three main con-vecting atmospheric cells in each hemisphere, named Hadley, Ferrel, and Polar cells. These play important roles in the distribution of different climate zones, as moist or rainy regions are located, in the tropics and at temperate latitudes, where the atmospheric cells are upwelling and release water. Deserts and dry areas are located around zones where the convect-ing cells downwell, bringing descending dry air into these regions.
The rotation of the Earth sets up systems of prevailing winds that modify the global convective atmospheric (and oceanic) circulation patterns. The spinning of the Earth sets up latitude-dependent airflow patterns, including the trade winds and westerlies. In addition, uneven heating of the Earth over land and ocean regions causes regional airflow patterns such as rising air over hot continents that must be replenished by air flowing in from the sides. The Coriolis force results from the rotation of the Earth and causes any moving air mass in the Northern Hemisphere to be deflected to the right and masses in the Southern Hemisphere to be deflected to the left. These types of patterns tend to persist for long periods of time and move large masses of air around the planet, redistributing heat and moisture and regulating the climate of any region.
Temperature, largely determined by latitude, is a major factor in the climate of any area. Polar regions experience huge changes in temperature between winter and summer months, largely a function of the wide variations in amount of incoming solar radiation and length of days. The proximity to large bodies of water such as oceans influences temperature, as water heats up and cools down much more slowly than land surfaces. Proximity to water therefore moderates temperature fluctuations. Altitude also influences temperature, with temperature decreasing with height.
Climate may change in cyclical or long-term trends, as influenced by changes in solar radiation, orbital variations of the Earth, amount of greenhouse gases in the atmosphere, or other phenomena such as El Niño or La Niña.
See also atmosphere; climate change; El Niño and the Southern Oscillation (ENSO); glacier, glacial systems; greenhouse effect; ice ages; Milankovitch cycles; plate tectonics; sea-level rise.
Ahrens, C. D. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 6th ed. Pacific Grove, Calif.: Brooks/Cole, 2000. Douglas, B., M. Kearney, and M. and S. Leatherman. Sea Level Rise: History and Consequence. San Diego, Calif.: Academic Press, International Geophysics Series 75, 2000.
Intergovernmental Panel on Climate Change 2007. Climate Change 2007: The Physical Science Basis. Contributions of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.) Cambridge: Cambridge University Press, 2007. Also available online. URL: http://www.ipcc.ch/index.htm. Accessed October 10, 2008.
National Aeronautic and Space Administration (NASA).
"Earth Observatory." Available online. URL: http://
earthobservatory.nasa.gov/. Accessed October 9,
2008, updated daily.
climate change The Earth has experienced many episodes of dramatic climate change, with different periods in Earth history seeing the planet much hotter or much colder than the present. There have been periods when the entire planet was covered in ice in a frozen, seemingly perpetual winter, then other times the Earth's surface was scorchingly hot and dry, and others when much of the planet felt like a hot, wet sauna. Scientists, including those from the Intergovernmental Panel on Climate Change, warn that the planet is currently experiencing global warming at a rapid pace, and there will be significant consequences for the people and ecosystems on the planet, as explained in sections below.
Many different variables control climate and can change the planet rapidly from one condition to another. Most of these are related to variations in the amount of incoming solar radiation caused by astronomical variations in the Earth's orbit. Other variables that can strongly influence long-term climate change include the amount of heat retained by the atmosphere and oceans, and on timescales of tens to hundreds of millions of years, the distribution of landmasses as they move about the planet from plate tectonics. Each of these changes operates with different time cycles, alternately causing the climate to become warmer and colder.
Significant long-term climate changes include the gradual alteration of the Earth's atmosphere from a global hothouse dominated by carbon dioxide (CO2) and other greenhouse gases when the Earth was young to an atmosphere rich in nitrogen and oxygen over the next couple billion years. Fortunately, during the early history of the Earth the Sun was less luminous, and the planet was not exceedingly hot. The motion of the continents has over time alternately placed them over the poles, which causes the continent to be covered in snow, reflecting more heat back to space and causing global cooling. Plate tectonics also has a complex interaction with concentrations of CO2 in the atmosphere, for instance, by uplifting carbonate rocks to be exposed to the atmosphere during continental collisions. The calcium carbonate (CaCO3) then combines with atmospheric CO2, depositing it in the oceans. Thus continental collisions and times of supercontinent formation are associated with drawdown and reduction of CO2 from the atmosphere, global cooling, and sea-level changes.
Orbital variations are the main cause of climate variations on more observable geological timescales.
The main time periods of these variations induce alternations of hotter and colder times, varying with frequencies of 100,000, 41,000, 23,000, and 19,000 years. To understand the complexity of natural climate variations, the contributions from each of these factors must be added together, forming a complex curve of climate warming and cooling trends. Built on top of these long-term climate variations that can change rapidly are shorter-term variations caused by changes in ocean circulation, sunspot cycles, and, finally, the contribution in the last couple of hundred years from the industry of humans, called anthropogenic changes. Deciphering which of these variables causes a particular percentage of the present global warming is no simple matter, and many political debates focus on who is to blame. Perhaps it is just as appropriate to focus on how we humans need to respond to global warming. Coastal cities may need to be moved, crop belts are migrating, climate zones are changing, river conditions will change, and many aspects of life that we are used to will be different. scientists are expending considerable effort to understand the climate history of the past million years in order to predict the future.
Continue reading here: Natural Longterm Climate Change
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