Page 389 - Earth's Climate Past and Future

GLOSSARY

(Many definitions apply specifically to their use in climate Barents ice sheet An ice sheet that covered the present-day
studies.) Barents Sea, north of Scandinavia, during orbital-scale glacia-
tion cycles.
ablation The loss of snow or ice from a glacier by melting,
calving, and other processes. basal slip Rapid sliding of an ice sheet across its water-
lubricated bed, especially in a region where ice streams lie
accumulation The addition of snow to a glacier.
above water-saturated sediment.
adiabatic Having to do with an increase in pressure that
raises the temperature of a parcel of air (adiabatic warming) or bedrock pinning point A high-standing protrusion of
a decrease in pressure that lowers that temperature (adiabatic bedrock that lies beneath the margin of an ice sheet and slows
cooling). the flow of ice into the ocean by frictional resistance.
benthic foraminifera Sand-sized organisms (protozoans)
aerosols Extremely small particles or droplets carried in sus-
pension in the air. that live on and in the seafloor and form shells of CaCO .
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albedo The decimal fraction or percentage of incoming solar biomass The amount of living matter in a region; also,
radiation reflected from a surface. organic matter used as a source of energy.
albedo-temperature feedback A positive feedback that biome A region on Earth with a distinctive community
amplifies an initial temperature change by altering the of plants.
amount of snow cover or sea ice and changing the amount biome model A vegetation model that simulates the major
of solar radiation absorbed by Earth’s surface. vegetation type (for example, grassland or desert scrub) that
aliasing The misleading (unrepresentative) signals that re- can exist in a region under a given set of climatic conditions.
sult from sampling a record of climate change at too low a biosphere The part of the Earth system that supports life,
resolution. including the oceans, land surfaces, soils, and atmosphere.
alkenones Complex organic molecules found in fossil shells biotic proxy An index of past climate change based on
of plant plankton and used to reconstruct past temperature. measurable variations in the type or abundance of climate-
amplitude Half of the height between peaks and troughs in a sensitive organisms.
regular wave form. Black Sea flood hypothesis The hypothesis that melting ice
Antarctic bottom water A dense, cold water mass that forms sheets caused rising ocean waters to flood into an ancient
near the Antarctic continent by extreme chilling of surface glacial lake, displacing humans and forming the Black Sea.
waters, sinks, and flows along the seafloor below a depth of 4 km. BLAG (spreading rate) hypothesis The hypothesis that
Antarctic intermediate water A water mass that forms tectonic-scale climate changes are driven by variations in the
in the Southern Ocean by chilling of seawater exposed in global average rate of seafloor spreading, which alter the
or near sea ice, sinks, and flows northward at depths of amount of CO introduced into the atmosphere.
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1to2km. boundary conditions The initial configuration of Earth’s
anthropogenic CO increase The steadily increasing con- properties chosen for a model simulation (such as land-sea
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centration of CO in the atmosphere over the last 200 years distribution, mountain elevation, and atmospheric CO con-
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due to human activities. centration).
anthropogenic forcing All human-related factors that cause Brown Cloud Haze of carbon aerosols emitted by human
climate change. activities, especially from cities in Asia.
aphelion The point in Earth’s slightly eccentric orbit at burial flux The rate of deposition of a substance in a sedi-
which it is farthest from the Sun. mentary reservoir measured in units of mass per unit of area
per unit of time.
asthenosphere A partially molten layer of rock in the upper
mantle that is weak enough to flow and cause movement of
the overlying lithospheric plate. C3 pathway The means by which trees and most shrubs
axial precession The wobbling movement of Earth’s axis of (about 95% of all land plants) obtain CO from the air during
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rotation, which causes it to point in different directions over a the initial step of photosynthesis.
cycle of 26,000 years. C4 pathway The means by which grasses that grow during
the warm season (about 5% of all land plants) obtain CO
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back radiation Electromagnetic energy at long (infrared) from the air during the initial step of photosynthesis.
wavelengths emitted from any material with a temperature calibration interval The interval of time (usually 50–100
above absolute zero (0 K). years) over which the width or density of tree rings can be
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