Glossary - Global Environmental Issues - page 193

3.5 million years ago and persisted until 10,000
years ago causing major disruption of land-forms,
drainage, animal communities and vegetation.
index cycle See zonal index .
Industrial Revolution A period of rapid transition from
an agricultural to an industrial society, beginning
in Britain in the mid-eighteenth century, and
spreading to other parts of the world in the next
two hundred years. It was characterized by a major
expansion in the use of coal as a fuel, in the steam
engine and in the iron industry. Although the
Industrial Revolution was a period of great
technical achievement and economic development,
it also marked the beginning of increasingly serious
environmental deterioration. Current
environmental issues such as acid rain, global
warming and atmospheric turbidity have their roots
in activities initiated or expanded during the
Industrial Revolution.
infrared radiation Low-energy, long-wave radiation
with wavelengths between 0.7 and 1,000 µm.
Terrestrial radiation is infrared. It is captured by
the atmospheric greenhouse gases and as a result
is responsible for the heating of the earth/
atmosphere system.
insolation Solar radiation entering the atmosphere.
interactive models General circulation models which
are programmed to deal with the progressive
change set in motion when one or more of the
components of the atmosphere is altered.
Intergovernmental Panel on Climate Change
(IPCC) A group of eminent scientists brought
together in 1988 by the World Meteorological
Organization (WMO) and the United Nations
Environment Program (UNEP) . It was charged
with assessing the overall state of research on
climate change so that potential environmental
and socio-economic impacts might be
evaluated, and appropriate response strategies
developed. Three reports were produced in
1990 and 1991.
Intertropical Convergence Zone (ITCZ) A thermal
low-pressure belt which circles the earth in
equatorial latitudes. It owes its origin to convective
uplift caused by strong surface heating, augmented
by converging air-flows from the northeast and
southeast Trade Winds. It lies between the tropical
Hadley Cells positioned north and south of the
equator. The ITCZ moves north and south with
the seasons bringing the rains to areas of seasonal
drought to areas such as the Sahel, India and
northern Australia.

invisible drought A form of drought that can be
identified only by sophisicated instrumentation and
statistical techniques. There may be no obvious lack
of precipitation, but moisture requirements are not
being met, the crops are not growing at their
optimum rate, and the potential yield is therefore
reduced.
ion An atom or group of atoms that has become
electrically charged by picking up or losing
electrons. Ions formed from metals are generally
positively charged (cations); those from non-metals
are negatively charged (anions).
IPCC Supplementary Report A report issued in 1992
by the Intergovernmental Panel on Climate Change
which generally confirmed the results of its earlier
assessments.
irrigation The provision of water for crops in areas
where the natural precipitation is inadequate for
crop growth.
isothermal layer An atmospheric layer in which the
lapse rate is neutral, that is the temperature remains
constant with increasing altitude. (See also
environmental lapse rate .)

J
jet stream A fast flowing stream of air in the upper
atmosphere at about the level of the tropopause .
Two well-defined jet streams, flowing from west
to east in a sinuous path around the earth, are
located in sub-tropical latitudes (the sub-tropical
jet) and in mid to high latitudes (the polar front
jet). An easterly tropical jet has also been
identified.

K
Krakatoa A volcanic island in the Sunda Strait,
Indonesia which erupted explosively in 1883
sending several tonnes of debris high into the
atmosphere. The volcanic dust circled the earth,
remaining in the upper atmosphere for several years
where it increased atmospheric turbidity .

L
La Niña An intermittent cold current flowing from
east to west across the equatorial Pacific Ocean, in
those years when El Niño is absent. It is caused by
strong equatorial easterly winds pushing cold water
upwelling off the South American coast, far out
into the ocean. Its influence appears to extend
beyond the Pacific, being associated with increased
precipitation in the Sahel and India.