Glossary - Global Environmental Issues - page 197

and oxygen is released, helping to maintain the
oxygen/carbon dioxide balance in the atmosphere.
phytoplankton Microscopic plants which live in the
upper layers of the oceans.
polar stratospheric clouds Clouds of ice particles which
form in the stratosphere above the poles during
the winter, (see also heterogeneous chemical
reactions .)
pollution (environmental) The contamination of the
physical and biological components of the earth/
atmosphere system to such an extent that normal
environmental processes are adversely affected.
polymer foams Synthetic foam produced by bubbling
chlorofluorocarbons through liquid plastic.
potential evapotranspiration (PE) The amount of
evaporation and transpiration that will take place
if sufficient moisture is available to fill the
environment's capacity for evapotranspiration .
Measurable evaporation ceases when water is no
longer available, but the environment may retain
the ability to cause additional evapotranspiration
through such elements as temperature, radiation,
humidity and wind. Potential evapotranspiration
is the theoretical value that represents that ability.
pre-Cambrian Shield An area of ancient, acidic rocks,
mainly igneous and metamorphic in origin, formed
perhaps as early as 4.5 billion years ago. Long
exposure to erosion has worn them down to the
subdued rounded landscapes found in northern
Canada, Sweden and Finland.
precipitation Any solid or liquid water particles falling
to the earth's surface from the atmosphere. It
includes rain, snow, hail and sleet.
precipitation scavenging A process by which rain and
snow wash particulate matter out of the
atmosphere, thus helping to cleanse it.
primary aerosols Large particles with diameters
between 1 and 100 µm. They include soil, dust and
a variety of industrial emissions formed by the
breakup of material at the earth's surface.
Pueblo drought A serious drought which struck the
territory of the Pueblo group of Indian tribes in the
south-western United States in the thirteenth century.

radiation blindness Loss of sight caused by damage to
the eye from exposure to excess solar radiation. It
usually takes the form of cataracts in which the
normally clear lens of the eye becomes opaque,
causing reduced light transmission and loss of visual
perception.
radiation scattering The disruption of the smooth flow
of radiation through the atmosphere, usually as a
result of paniculate matter in the energy path.
radiation spectrum see electromagnetic spectrum .
radiative-convective models One-dimensional climate
models incorporating global-scale radiative and
convective processes at different levels in the
atmosphere, used to estimate temperature change
initiated by changing atmospheric aerosol levels.
radiative forcing agent Any factor capable of
disturbing the energy balance of the earth/
atmosphere system.
RAINS A computer model developed to study acid
rain in Asia. Similar to a model developed for the
European Community, it will allow researchers to
alert Asian governments to the extent and intensity
of the problem.
recharge rate The rate at which water withdrawn from
the groundwater system is replaced by
precipitation .
recycling The recovery of waste material for
reprocessing into new products, or the reuse of
discarded products.
remote sensing The observation of the surface of the
earth from a distance by means of sensors. Aerial
photography was the earliest form of remote
sensing, but satellite observation is now most
common, involving the creation of simple
photographic images or the collection of data in
digital form.
retrofitting The adaptation of an existing structure or
appliance to meet needs which did not exist when
the structure or appliance was first constructed.
Rio Declaration A declaration of global principles on
the theme of economically and environmentally
sound development. Along with Agenda 21, it
represented the culmination of the activities of the
United Nations Conference on Environment and
Development (UNCED) .
Rossby waves Longwaves in the circumpolar westerly
airflow in the upper atmosphere, first described by
Carl Rossby in the 1930s. The flow pattern
followed by the waves is quite variable and difficult

R
radiation absorption The intake of radiant energy by
an object, causing the temperature of the object to
rise, and allowing it to become a radiating body in
its own right.