Page 393 - Earth's Climate Past and Future

GLOSSARY 369

Kelvin A scale on which temperature is measured in Celsius mass balance model A model that tracks the movement of
degree intervals and on which water freezes at 273 K and boils materials within Earth’s climate system using conservation of
at 373K, and all motion ceases at 0 K. mass to balance inputs and outputs among different reservoirs.
mass spectrometer An instrument that measures different
La Niña A pattern opposite from that of El Niño, in which isotopes of the same element (such as 16O vs. 18O and 12C
sea surface temperatures in the tropical eastern Pacific, off the vs. 13C) by separating them by mass.
west coast of South America, become unusually cold.
mass wasting A downhill movement of rock or soil under
lapse rate The rate at which temperature falls with elevation in the force of gravity.
the atmosphere, averaging 6.5°C of cooling for each kilometer Maunder sunspot minimum An interval between 1645 and
of altitude, but more for dry air and less for moist air.
1715 A.D. when astronomers observed very few sunspots on
latent heat The quantity of heat gained or lost as a substance the Sun’s surface.
changes state (liquid, solid, or gas) at a given temperature and
pressure. medieval climatic optimum An interval between 1100 and
1300 A.D. in which some northern hemisphere regions were
latent heat of melting The amount of heat gained as ice warmer than in the Little Ice Age that followed.
melts or released as water freezes.
Mediterranean overflow water A water mass that forms in
latent heat of vaporization The amount of heat gained
the northern Mediterranean Sea by winter chilling of salty
when water turns to water vapor or released when water vapor
surface waters and flows into the North Atlantic at a depth of
condenses back to water.
1 km.
Laurentide ice sheet The largest of the northern hemi- methane clathrate A partly frozen slushy mix of methane
sphere ice sheets that grow and shrink at orbital cycles, cover- gas (CH ) and ice.
ing east-central Canada and the northern United States east 4
of the Rockies. Mg/Ca ratios The ratio of the elements Mg and Ca in shells
of foraminifera, an index of past temperature changes.
lichen Primitive mosslike vegetation that lives on bare rock
surfaces, uses sunlight to secrete acids and weather the rock, Milankovitch theory The theory that orbitally controlled
and slowly grows in a nearly circular shape. fluctuations in high-latitude solar radiation (insolation) dur-
ing summer control the size of ice sheets through their effect
lithosphere The outer rigid shell of Earth (including the on melting.
upper mantle and oceanic and continental crust), characterized
by strong, rocklike properties and divided into plates that millennial oscillations Fluctuations in climate lasting thou-
move as rigid units during plate tectonic processes. sands of years and generally larger during glacial than inter-
glacial intervals.
Little Ice Age An interval between approximately 1400 and
1900 A.D. when temperatures in the northern hemisphere modulation The tendency for peaks and troughs in a wave
were generally colder than today’s, especially in Europe. form to vary in size in a regular way, such that clusters of large
peaks and troughs alternate with clusters of smaller ones.
loess Silt-sized windblown glacial sediment.
moraine A pile of unsorted rubble (till) deposited by a gla-
longwave radiation Energy emitted in the infrared part of
the electromagnetic spectrum by materials having a tempera- cier at its margin.
ture above absolute zero (0 K). monsoon Winds that reverse direction seasonally, blowing
onshore in summer and offshore in winter because of different
macrofossils Larger fragments of vegetation (such as needles, rates of heating and cooling of land and water.
twigs, or cones) that prove the local presence of vegetation on Monterey hypothesis The hypothesis that increased rates of
past landscapes, used as a supplement to pollen analysis. burial of organic carbon on the margins of the Pacific Ocean
magnetic field The lines of force that are generated by 17 Myr ago reduced CO levels in the surface ocean and
2
motion in Earth’s outer core and cause iron-bearing materials atmosphere.
to align in specific directions in relation to the magnetic north mountain glacier A body of ice tens to hundred of meters
pole. thick and kilometers in length confined to a valley at a high
magnetic lineations Long, stripelike regions of ocean crust elevation. A mountain ice cap is a similar-sized body of ice
marked by stronger or weaker magnetism acquired when the lying on the rounded summit of a mountain.
crust formed by cooling from molten magma at a ridge crest.
mantle The middle (and largest) layer of the solid Earth, no-analog vegetation A combination of types of vegetation
lying beneath the crust and above the core and composed in the past for which no similar (analogous) combination
of silicate minerals. exists today.
marine ice sheet An ice sheet whose base lies below sea nonlinear response A climatic response that occurs on other
level, as in western Antarctica. than a simple one-for-one basis in relation to the forcing.
mass balance The method of tracking the movement of North Atlantic deep water A water mass that forms in the
materials within Earth’s climate system by applying the law high-latitude North Atlantic Ocean by winter chilling of salty
of conservation of mass. surface water, sinks, and flows southward at depths of 2 to 4 km.