Botkin Environmental Science Earth as Living Planet 8th txtbk

Glossary G-19
Time series The set of estimates of some variable over a
number of years.
Tolerance The ability to withstand stress resulting from exposure
to a pollutant or other harmful condition.
Tornado A funnel-shaped cloud of violently rotating air that
extends downward from large thunder storms to contact
the surface of earth.
Total fertility rate (TFR) The average number of children
expected to be born to a woman during her lifetime. (Usually
defined as the number born to a woman between the
ages of 15 and 44, taken conventionally as the lower and
upper limit of reproductive ages for women.)
Toxic Harmful, deadly, or poisonous.
Toxicology The science concerned with the study of poisons
(or toxins) and their effects on living organisms. The subject
also includes the clinical, industrial, economic, and legal
problems associated with toxic materials.
Transuranic waste Radioactive waste consisting of human-made
radioactive elements heavier than uranium. Includes clothing,
rags, tools, and equipment that has been contaminated.
Trophic level In an ecological community, all the organisms
that are the same number of food-chain steps from the
primary source of energy. For example, in a grassland the
green grasses are on the first trophic level, grasshoppers are
on the second, birds that feed on grasshoppers are on the
third, and so forth.
Trophic level efficiency The ratio of the biological production
of one trophic level to the biological production of the next
lower trophic level.
Troposphere The atmospheric zone from the surface of the
Earth to an altitude of approximately 20 kilometers above
the Earth. The troposphere is the zone of the atmosphere
we are most familiar with because we spend most of our
lives in it.
Tundra The treeless land area in alpine and arctic areas characterized
by plants of low stature and including bare areas
without any plants and areas covered with lichens, mosses,
grasses, sedges, and small flowering plants, including low
shrubs.
Ubiquitous species Species that are found almost anywhere
on Earth.
Ultraviolet A (UVA) The longest wavelength of ultraviolet
radiation (0.32–0.4 micrometers), not affected by stratospheric
ozone, and transmitted to the surface of Earth.
Ultraviolet B (UVB) Intermediate-wavelength radiation
which is the ozone problem. Wavelengths are approximately
0.28–0.32 micrometers and are the most harmful
of the ultraviolet radiation types. Most of this radiation is
absorbed by stratospheric ozone, and depletion of ozone
has led to increased ultraviolet B radiation reaching Earth.
Ultraviolet C (UVC) The shortest wavelength of the ultraviolet
radiation with wavelengths of approximately 0.2–0.28
micrometers. It is the most energetic of the ultraviolet radiation
and is absorbed strongly in the atmosphere. Only a negligible
amount of Ultraviolet C reaches the surface of Earth.
Ultraviolet (UV) index An index based on the exposure to
ultraviolet radiation to humans. Varies from low to ex-
treme and is useful for people wishing recommendation of
how much exposure to the sun they should incur and how
much sun block to use.
Undernourishment The lack of sufficient calories in available
food, so that one has little or no ability to move or work.
Uneven-aged stands A forest stand with at least three distinct
age classes.
Unified soil classification system A classification of soils,
widely used in engineering practice, based on the amount
of coarse particles, fine particles, or organic material.
Uniformitarianism The principle stating that processes that
operate today operated in the past. Therefore, observations
of processes today can explain events that occurred in the
past and leave evidence, for example, in the fossil record or
in geologic formations.
Urban dust dome Polluted urban air produced by the
combination of lingering air and abundance of particulates
and other pollutants in the urban air mass.
Urban forestry The practice and profession of planting and
maintaining trees in cities, including trees in parks and
other public areas.
Urban-runoff naturalization An emerging bioengineering
technology with the objective to treat urban runoff before
it reaches streams, lakes, or the ocean.
Utilitarian justification for the conservation of nature An
argument for the conservation of nature on the grounds
that the environment, an ecosystem, habitat, or species
provides individuals with direct economic benefit or is
directly necessary to their survival.
Utility Value or worth in economic terms.
UVA See Ultraviolet A.
UVB See Ultraviolet B.
UVC See Ultraviolet C.
Vadose zone Zone or layer above the water table where water
may be stored as it moves laterally or down to the zone of
saturation. Part of the vadose zone may be saturated part
of the time.
Variable, dependent A variable that changes in response to
changes in an independent variable; a variable taken as the
outcome of one or more other variables.
Variable, independent In an experiment, the variable that is
manipulated by the investigator. In an observational study,
the variable that is believed by the investigator to affect an
outcome, or dependent, variable.
Variable, manipulated See Variable, independent.
Variable, responding See Variable, dependent.
Virgin forest A forest that has never been cut.
Virtual water The amount of water necessary to produce a
product, such as rice or, in industry, an automobile.
Volcanic eruption Extrusion at the surface of Earth of molten
rock (magma). May be explosive and violent or less energetic
lava flows.
Vulnerable species Another term for threatened species—
species experiencing a decline in the number of individuals.
Waldsterben German phenomenon of forest death as the
result of acid rain, ozone, and other air pollutants.