Page 392 - Earth's Climate Past and Future

368 GLOSSARY

Gondwana The large continent that existed in the southern hydrothermal Characterized by the circulation of hot fluids
hemisphere before the creation of the giant continent Pangaea. through rocks in Earth’s outer crust, as at the Mid-Ocean
Ridge system.
greenhouse debate The controversy over the extent to
which rising levels of atmospheric greenhouse gases have hypothesis An explanation of observations based on physical
warmed Earth’s climate during the last 200 years. principles.
greenhouse effect The warming of Earth’s surface and hypsometric curve A graph that summarizes the proportions
lower atmosphere that occurs when its own emitted infrared of Earth’s surface that lie at various altitudes above and depths
heat is trapped and reradiated downward by greenhouse gases. below sea level.
greenhouse era An interval of warm climate on Earth, such
ice dome A high, gently sloping central region of an ice sheet
as the Cretaceous, with ice sheets absent even in polar regions.
in which snow accumulates and away from which ice flows
greenhouse gases Gases such as water vapor (H Ov), carbon
2 slowly.
dioxide (CO ), and methane (CH ), which trap outgoing
2 4 ice-driven response A climate change produced by fluctua-
infrared radiation emitted by Earth’s surface and warm the
atmosphere. tions in the size of an ice sheet.
ice-elevation feedback The positive feedback that results
greenhouse surprise A climate change in the greenhouse
world of the future that cannot be predicted. when an ice sheet grows to a higher elevation at which accu-
mulation exceeds ablation.
grid boxes Geometric units within climate models that have
ice flow model A model that simulates ice sheet processes of
uniform climatic characteristics and exchange heat, energy,
snow accumulation, internal ice flow, and ablation.
and other properties with adjoining grid boxes.
icehouse era An interval of cold climate on Earth, such as
Gulf Stream A narrow current of warm water that emerges the present, with ice sheets present in polar regions.
from the Gulf of Mexico through the Florida Straits and
flows northward along the southeastern coast of the United ice lobe A rounded or arc-shaped outward protrusion of the
States. margin of an ice sheet.
ice-rafted debris Sediments of widely ranging sizes eroded
gyre A spinning cell of water in an ocean basin, particularly at
a subtropical latitude. from the land by ice, carried to the ocean, and deposited on
the seafloor.
ice saddle A ridge that connects multiple domes of an ice
Hadley cell An atmospheric circulation cell in which air rises
in the tropics, flows to the subtropics, sinks near 30° latitude, sheet at a slightly lower elevation.
and flows back toward the tropics as surface trade winds. ice shelf A wide body of ice usually hundreds of meters thick
that is fed by ice flowing off a continent, partially floats on
half-life The time required for half the number of atoms of a
radioactive isotope to decay. seawater, and produces icebergs as blocks of ice break off.
ice stream A region of an ice sheet in which the motion of
harmonics Secondary cycles related to a wavelike climatic ice is unusually rapid, generally because of water-saturated
response with a period N, occurring at periods of N/2, N/3, sediments at the base of the ice.
N/4, and so on.
igneous rock Rock formed by the cooling and solidification
hardwood forest A forest comprising leaf-bearing (decidu- of molten magma.
ous) trees.
insolation The amount of solar radiation arriving at the top
heat capacity The amount of heat energy required to raise of Earth’s atmosphere by latitude and by season.
the temperature of 1 gram of a substance by 1°C.
instrument records Records of climate change measured by
Heinrich event An interval of rapid flow of icebergs from devices made by humans, from early thermometers through
the margins of ice sheets into the North Atlantic Ocean, caus- modern satellite-mounted instruments.
ing deposition of sediment layers rich in debris eroded from
the land. Intergovernmental Panel on Climate Change (IPCC) A
large international group of scientists who reflect the current
historical archives Sources of information on climate based scientific consensus on the impact of greenhouse gases.
on human observations of natural phenomena made before intertropical convergence zone (ITCZ) A narrow region
the era of instrument measurements.
within the tropics where warm moist air rises, cools, and loses
hot spot A point on the surface of a lithospheric plate where its water vapor in heavy tropical rainfall.
magma rising from below causes frequent volcanic activity.
iron fertilization hypothesis The hypothesis that iron-rich
hydrologic cycle The movement of water and water vapor dust blown from the continents during glaciations enhances the
among the atmosphere, land, and ocean through evaporation, productivity of the surface ocean, sends CO into the deep ocean,
2
precipitation, runoff, and subsurface groundwater flow. and reduces the concentration of CO in the atmosphere.
2
hydrolysis A form of chemical weathering in which water
reacts with silicate minerals rich in silicon and oxygen to jet stream A narrow meandering stream of air moving
produce dissolved ions removed in rivers and clays left on the rapidly (generally from west to east) at a high latitude and at
landscape. an altitude averaging 10 km.