Reservoirs speed up Earth's spin.Earth Science People have stored so much water in artificial reservoirs in recent decades that they have subtly altered the planet's rotation. Water impoundment An action taken by the president in which he or she proposes not to spend all or part of a sum of money appropriated by Congress. The current rules and procedures for impoundment were created by the Congressional Budget and Impoundment Control Act of 1974 (2 U.S.C.A. has shortened the length of the day and shifted Earth's spin axis by tiny amounts, reports Ben jamin Fong Chao, a geophysicist at NASA's Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md. Over the last 40 years, people have pooled roughly 10 trillion tons of water in reservoirs, most of them located in the Northern Hemisphere. The process has shifted water from the oceans to the continents, tending to reduce mass around Earth's equator and increase mass in the northern part of the globe. The shift has quickened Earth's spin by placing water closer to the axis of rotation Noun 1. axis of rotation - the center around which something rotates axis mechanism - device consisting of a piece of machinery; has moving parts that perform some function , much as a skater might bring his or her arms close to the body in order to spin faster. Geophysicists measure changes in Earth's spin in terms of the length of the day. A faster spin shortens the day. "Due to the reservoir effect, the day 40 years ago was longer than today by about 8 millionths of a second," says Chao. This change is only one-hundredth the size of annual fluctuations in day length caused by natural forces, says Chao, who reports his findings in the Dec. 15, 1995 Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or . Earth's spin slows down and speeds up in response to many factors, including atmospheric pressure atmospheric pressure or barometric pressure Force per unit area exerted by the air above the surface of the Earth. Standard sea-level pressure, by definition, equals 1 atmosphere (atm), or 29.92 in. (760 mm) of mercury, 14.70 lbs per square in., or 101. systems and ocean currents. Because reservoirs are not placed symmetrically around the globe, water storage has also changed the planet's axis. Since 1940, impoundment has pushed the axis of rotation about 60 centimeters away from the North Pole North Pole, northern end of the earth's axis, lat. 90°N. It is distinguished from the north magnetic pole. U.S. explorer Robert E. Peary is traditionally credited as being the first to reach (1909) the North Pole. In 1926, Richard E. toward western Canada. Such a shift is significant, says Chao. It equals 5 percent of the natural axis drift over the last 100 years. The creation of reservoirs, he says, "is the only human activity that's big enough to cause any appreciable change in these global phenomena." |
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