Page 391 - Earth's Climate Past and Future

GLOSSARY 367

daughter isotope An isotope produced by radiometric decay equilibrium A state of climatic stability toward which the cli-
of another isotope. mate system is moving and at which it will eventually remain,
unless disturbed.
deforestation Cutting of forests by humans to clear land for
agriculture and other processes. equilibrium line The level in the atmosphere separating the
zones of net addition and loss of ice.
deglacial two-step The irregular melting of ice sheets dur-
ing the most recent deglaciation: fast-slow-fast. equinoxes The two times during each year (spring and
autumn) when the lengths of days and nights are equal.
d13C aging The gradual shift toward more negative d13C
values in slow-moving deep water caused by the downward equivalent CO Changes in all greenhouse gases expressed
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rain of 12C-rich organic matter from overlying surface water. in terms of an equivalent change in atmospheric CO concen-
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trations.
dendroclimatology The methods used to extract climate
signals from changes in the width or density of tree rings, eustatic Characterized by changes in sea level that are global
both of which are sensitive to extremes of temperature and in scale, rather than the result of local factors such as tectonic
precipitation. uplift or subsidence of the land.
dew point The temperature at which cooling air becomes evaporites Minerals or rocks formed by precipitation of
fully saturated with water vapor and permits condensation. crystals from water evaporating in restricted basins in arid cli-
mates.
diatoms Silt-sized algae that live in surface waters of lakes,
rivers, and oceans and form shells of opal (SiO ·H O). evolution The process by which particular forms of life give
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rise to other similar forms by gradual genetic changes.
diffusion The transfer of a property such as heat by random,
small-scale movements from a region of higher to lower con- faculae Bright rings that surround sunspots and emit large
centration. amounts of solar radiation.
diluvial hypothesis The hypothesis that unsorted sediments Fahrenheit A temperature scale on which water freezes at
found on northern continents resulted from a great flood; 32° and boils at 212°.
these deposits are now recognized as deposits from glaciers. faint young Sun paradox The paradox in which astronomical
dissolution A form of chemical weathering in which rocks models indicate a much weaker Sun through Earth’s early his-
such as limestone (CaCO ) or rock salt (NaCl) are dissolved tory but geologic evidence shows that Earth never froze.
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by water and produce ions that are removed by rivers. feedback A process internal to Earth’s climate system that
divergent margin A boundary between two lithospheric plates acts either to amplify changes in climate (positive feedback) or
that are moving apart, usually at the crest of an ocean ridge. to moderate them (negative feedback).
filtering The technique of extracting and isolating the shape of
Earth system The complex system of Earth’s atmosphere, cycles at specific wavelengths or periods from complex signals.
hydrosphere, biosphere, and lithosphere, through which fluvial sediments Sediments deposited by the action of water.
energy and matter circulate. forcing Any process or disturbance that drives changes in cli-
eccentricity The extent to which Earth’s orbit around the mate.
Sun departs from a perfect circle. fractionation A process favoring the transfer of one isotope
elastic Capable of deforming rapidly under pressure (as is of an element more than another.
bedrock under the pressure of a glacier) and rebounding when frequency The number of full wave forms (each with one
the pressure is removed. peak and one trough) that occur within a defined interval of
electromagnetic radiation Self-propogating electric-mag- time (usually one year). Also, the inverse of the period.
netic waves, which include visible light as well as infrared and
ultraviolet waves. Gaia hypothesis A hypothesis that life regulates climate
electromagnetic spectrum The complete range of electro- on Earth.
magnetic radiation at differing wavelengths. general circulation model (GCM) A three-dimensional
El Niño A climatic pattern that recurs at intervals of 2 to 7 computer model of the global atmosphere (or ocean) that
years and is marked by warm sea surface temperatures in the simulates temperature, precipitation, winds, and atmospheric
eastern tropical Pacific, off the west coast of South America. pressure.
enhanced greenhouse effect Trapping of Earth’s back radi- geochemical model A model that quantifies the movement
ation by greenhouse gases produced by humans, in addition to of geochemical tracers (minerals, elements, or isotopes)
the warming caused by natural greenhouse gases. among reservoirs in the climate system.
ENSO (El Niño Southern Oscillation) The combined geochemical tracer A chemical element or isotope whose
oscillations of El Niño (temperature changes in the eastern movement between reservoirs in the climate system can be
Pacific) and the southern oscillation (atmospheric pressure quantitatively tracked.
changes in the western and south-central Pacific). geological–geochemical proxy An index of past climate
eolian sediments Fine sediments deposited by the action change based on measurable variations in physical or chemical
of wind. properties of sediments, ice, or other archives.