Absorption of Radiation. The uptake of radiation
by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted. Acid Rain. Also known as "acid deposition." Acidic aerosols
in the atmosphere are removed from the atmosphere by wet deposition (rain,
snow, fog) or dry deposition (particles sticking to vegetation). Acidic aerosols are
present in the atmosphere primarily due to discharges of gaseous sulfur oxides (sulfur
dioxide) and nitrogen oxides from both anthropogenic
and natural sources. In the atmosphere these gases combine with water to form acids.
Aerosols. Particles of matter, solid or liquid, larger
than a molecule but small enough to remain suspended in the atmosphere.
Natural sources include salt particles from sea spray and clay particles as a result of
weathering of rocks, both of which are carried upward by the wind. Aerosols can also
originate as a result of human activities and in this case are often considered pollutants.
See also Sulfate Aerosols.
Albedo. The ratio of reflected to incident light; albedo
can be expressed as either a percentage or a fraction of 1. Snow covered areas have a high
albedo (up to about 0.9 or 90%) due to their white color, while vegetation has a low
albedo (generally about 0.1 or 10%) due to the dark color and light absorbed for photosynthesis.
Clouds have an intermediate albedo and are the most important contributor to the Earth's
albedo. The Earth's aggregate albedo is approximately 0.3.
Alliance of Small Island States (AOSIS). The group of
Pacific and Caribbean nations who call for relatively fast action by developed nations to
reduce greenhouse gas emissions. The AOSIS countries fear the
effects of rising sea levels and increased storm activity predicted to accompany global
warming. Its plan is to hold Annex I Parties to a 20 percent
reduction in carbon dioxide emissions by the year 2005.
Annex I Parties. Industrialized countries that, as parties
to the Framework Convention on Climate Change, have pledged to reduce their greenhouse
gas emissions by the year 2000 to 1990 levels. Annex I Parties consist of countries
belonging to the Organization for Economic Cooperation and Development (OECD) and
countries designated as Economies-in-Transition.
Anthropogenic. Derived from human activities.
Atmosphere. The mixture of gases surrounding the Earth.
The Earth's atmosphere consists of about 79.1% nitrogen (by volume), 20.9% oxygen, 0.036%
carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a
number of layers according to its mixing or chemical characteristics, generally determined
by its thermal properties (temperature). The layer nearest the Earth is the troposphere,
which reaches up to an altitude of about 8 km (about 5 miles) in the polar regions and up
to 17 km (nearly 11 miles) above the equator. The stratosphere, which
reaches to an altitude of about 50 km (31 miles) lies atop the troposphere. The mesosphere
which extends up to 80-90 km is atop the stratosphere, and finally, the thermosphere, or
ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is
relatively little mixing of gases between layers.
Baseline Emissions. The emissions that would occur
without policy intervention (in a business-as-usual scenario). Baseline estimates are
needed to determine the effectiveness of emissions reduction programs (often called
Berlin Mandate. A ruling negotiated at the first Conference
of the Parties (CoP 1), which took place in March, 1995, concluding that the
present commitments under the Framework Convention on Climate Change are not adequate.
Under the Framework Convention, developed countries pledged to take measures aimed at
returning their greenhouse gas emissions to 1990 levels by the
year 2000. The Berlin Mandate establishes a process that would enable the Parties to take
appropriate action for the period beyond 2000, including a strengthening of developed
country commitments, through the adoption of a protocol or other legal instruments.
Biogeochemical Cycle. The chemical interactions
that take place among the atmosphere, biosphere , hydrosphere,
Biomass. Organic nonfossil material of biological origin.
For example, trees and plants are biomass.
Biomass Energy. Energy produced by combusting
renewable biomass materials such as wood. The carbon dioxide emitted
from burning biomass will not increase total atmospheric carbon dioxide if this
consumption is done on a sustainable basis (i.e., if in a given period of time, regrowth
of biomass takes up as much carbon dioxide as is released from biomass combustion).
Biomass energy is often suggested as a replacement for fossil fuel combustion
which has large greenhouse gas emissions.
Biosphere. The region on land, in the oceans, and in the
atmosphere inhabited by living organisms.
Borehole. Any exploratory hole drilled into the Earth or
ice to gather geophysical data. Climate researchers often take ice core
samples, a type of borehole, to predict atmospheric composition in earlier years.
Carbon Cycle. The global scale exchange of carbon
among its reservoirs, namely the atmosphere, oceans, vegetation, soils, and geologic
deposits and minerals. This involves components in food chains, in the atmosphere
as carbon dioxide, in the hydrosphere and in the geosphere.
Carbon Dioxide (CO2). The greenhouse
gas whose concentration is being most affected directly by human activities. CO2
also serves as the reference to compare all other greenhouse gases (see carbon
dioxide equivalents). The major source of CO2 emissions
is fossil fuel combustion. CO2 emissions are also a product of
forest clearing, biomass burning, and non-energy production processes such
as cement production. Atmospheric concentrations of CO2 have been
increasing at a rate of about 0.5% per year and are now about 30% above preindustrial
Carbon Dioxide Equivalent (CDE). A metric
measure used to compare the emissions from various greenhouse gases
based upon their global warming potential (GWP). Carbon dioxide equivalents
are commonly expressed as "million metric tons of carbon dioxide equivalents
(MMTCDE)" or "million short tons of carbon dioxide equivalents (MSTCDE)"
The carbon dioxide equivalent for a gas is derived by multiplying the tons of the gas by
the associated GWP.
MMTCDE= (million metric tons of a gas) * (GWP of the gas)
For example, the GWP for methane is 24.5. This means that emissions of one million
metric tons of methane is equivalent to emissions of 24.5 million metric
tons of carbon dioxide. Carbon may also be used as the reference and other greenhouse
gases may be converted to carbon equivalents. To convert carbon to carbon
dioxide, multiply the carbon by 44/12 (the ratio of the molecular weight of carbon dioxide
Carbon Equivalent (CE). A metric measure used to
compare the emissions of the different greenhouse gases based upon their global
warming potential (GWP). Greenhouse gas emissions in the U.S. are most commonly
expressed as "million metric tons of carbon equivalents" (MMTCE). Global warming
potentials are used to convert greenhouse gases to carbon dioxide equivalents.
Carbon dioxide equivalents can then be converted to carbon equivalents by multiplying the carbon
dioxide equivalents by 12/44 (the ratio of the molecular weight of carbon to
carbon dioxide). Thus, the formula to derive carbon equivalents is:
MMTCE = (million metric tons of a gas) * (GWP of the gas) * (12/44)
Carbon Sequestration. The uptake and storage
of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and
store the carbon. Fossil fuels were at one time biomass and continue to
store the carbon until burned.
Carbon Sinks. Carbon reservoirs and conditions that
take in and store more carbon (carbon sequestration) than they release.
Carbon sinks can serve to partially offset greenhouse gas emissions.
Forests and oceans are common carbon sinks.
Chlorofluorocarbons and Related Compounds.
This family of anthropogenic compounds includes chlorofluorcarbons (CFCs),
bromofluorcarbons (halons), methyl chloroform, carbon tetrachloride, methyl
bromide, and hydrochlorofluorcarbons (HCFCs). These compounds have been shown to deplete
stratospheric ozone, and therefore are typically referred to as ozone
depleting substances. The most ozone-depleting of these compounds are being phased
out under the Montreal Protocol.
Climate. The average weather (usually taken
over a 30-year time period) for a particular region and time period. Climate is not the
same as weather, but rather, it is the average pattern of weather for a particular region.
Weather describes the short-term state of the atmosphere. Climatic elements include
precipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog,
frost, and hail storms, and other measures of the weather.
Climate Change (also referred to as 'global climate
change'). The term 'climate change' is sometimes used to refer to all forms of
climatic inconsistency, but because the Earth's climate is never static, the term is more
properly used to imply a significant change from one climatic condition to another. In
some cases, 'climate change' has been used synonymously with the term, 'global
warming'; scientists however, tend to use the term in the wider sense to also
include natural changes in climate. See also Enhanced Greenhouse Effect.
Climate Change Action Plan (). Unveiled in October, 1993 by
President Clinton, the CCAP is the U.S. plan for meeting its pledge to reduce greenhouse
gas emissions under the terms of the Framework Convention on Climate Change (FCCC). The
goal of the CCAP is to reduce U.S. emissions of anthropogenic greenhouse
gases to 1990 levels by the year 2000. The CCAP, which consists of some 50
voluntary federal programs that span all sectors of the economy, uses a win-win approach
by helping program partners save energy, save money, and gain access to clean technology
while also reducing greenhouse gas emissions.
Climate Feedback. An atmospheric, oceanic,
terrestrial, or other process that is activated by the direct climate change
induced by changes in radiative forcing. Climate feedbacks may increase (positive
feedback) or diminish (negative feedback) the magnitude of the direct climate change.
Climate Lag. The delay that occurs in climate
change as a result of some factor that changes only very slowly. For example, the
effects of releasing more carbon dioxide into the atmosphere
may not be known for some time because a large fraction is dissolved in the ocean and only
released to the atmosphere many years later.
Climate Model. A quantitative way of representing the
interactions of the atmosphere, oceans, land surface, and ice. Models can range from
relatively simple to quite comprehensive. Also see General Circulation Model.
Climate Modeling. The simulation of the climate
using computer-based models. Also see General Circulation Model.
Climate Sensitivity. The equilibrium response
of the climate to a change in radiative forcing; for example,
a doubling of the carbon dioxide concentration.
Climate System (or Earth System). The atmosphere,
the oceans, the biosphere, the cryosphere, and the geosphere,
together make up the climate system.
Cogeneration. The process by which two different and
useful forms of energy are produced at the same time. For example, while boiling water to
generate electricity, the leftover steam can be sold for industrial processes or space
Compost. Decayed organic matter that can be used as a
fertilizer or soil additive.
Conference of the Parties (CoP). The CoP is the
collection of nations which have ratified the Framework Convention on Climate Change
(FCCC), currently over 150 strong, and about 50 Observer States. The primary role
of the CoP is to keep the implementation of the Convention under review and to take the
decisions necessary for the effective implementation of the Convention. The first CoP (CoP
1) took place in Berlin from March 28th to April 7th, 1995, and was attended by over 1000
observers and 2000 media representatives.
Cryosphere. The frozen part of the Earth's surface. The
cryosphere includes the polar ice caps, continental ice sheets, mountain glaciers, sea
ice, snow cover, lake and river ice, and permafrost.
Deforestation. Those practices or processes that
result in the change of forested lands to non-forest uses. This is often cited as one of
the major causes of the enhanced greenhouse effect for two reasons: 1) the
burning or decomposition of the wood releases carbon dioxide; and 2) trees
that once removed carbon dioxide from the atmosphere in the process of photosynthesis
are no longer present and contributing to carbon storage.
Desertification. The progressive destruction or
degradation of existing vegetative cover to form desert. This can occur due to
overgrazing, deforestation, drought, and the burning of extensive areas.
Once formed, deserts can only support a sparse range of vegetation. Climatic effects
associated with this phenomenon include increased albedo, reduced
atmospheric humidity, and greater atmospheric dust (aerosol) loading.
El Nino. A climatic phenomenon occurring irregularly, but
generally every 3 to 5 years. El Ninos often first become evident during the Christmas
season (El Nino means Christ child) in the surface oceans of the eastern tropical Pacific
Ocean. The phenomenon involves seasonal changes in the direction of the tropical winds
over the Pacific and abnormally warm surface ocean temperatures. The changes in the
tropics are most intense in the Pacific region, these changes can disrupt weather patterns
throughout the tropics and can extend to higher latitudes, especially in Central and North
America. The relationship between these events and global weather patterns are currently
the subject of much research in order to enhance prediction of seasonal to interannual
fluctuations in the climate.
Emissions. The release of a substance (usually a gas
when referring to the subject of climate change) into the atmosphere.
Enhanced Greenhouse Effect. The natural greenhouse
effect has been enhanced by anthropogenic emissions of greenhouse
gases. Increased concentrations of carbon dioxide, methane,
and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically
important gases caused by human activities such as fossil fuel consumption and adding
waste to landfills, trap more infra-red radiation, thereby exerting a
warming influence on the climate. See Climate Change and
Evapotranspiration. The sum
of evaporation and plant transpiration. Potential evapotranspiration is the amount of
water that could be evaporated or transpired at a given temperature and humidity, if there
was plenty of water available. Actual evapotranspiration can not be any greater than
precipitation, and will usually be less because some water will run off in rivers and flow
to the oceans. If potential evapotranspiration is greater than actual precipitation, then
soils are extremely dry during at least a major part of the year.
Feedback Mechanisms. A mechanism that connects one aspect
of a system to another. The connection can be either amplifying (positive feedback) or
moderating (negative feedback). See also Climate Feedback.
Carbon Dioxide Fertilization. An expression
(sometimes reduced to 'fertilization') used to denote increased plant growth due to a
higher carbon dioxide concentration.
Fertilization. A term used to denote efforts to
enhance plant growth by increased application of nitrogen-based fertilizer or increased
deposition of nitrates in precipitation.
Fluorocarbons. Carbon-fluorine compounds that often
contain other elements such as hydrogen, chlorine, or bromine. Common fluorocarbons
include chlorofluorocarbons and related compounds (also know as ozone
depleting substances), hydrofluorocarbons (HFCs), and perfluorcarbons
Forcing Mechanism. A process that alters the energy
balance of the climate system, i.e. changes the relative balance between
incoming solar radiation and outgoing infrared radiation from
Earth. Such mechanisms include changes in solar irradiance, volcanic eruptions, and
enhancement of the natural greenhouse effect by emission of carbon dioxide.
See also Radiative Forcing.
Fossil Fuel. A general term for combustible geologic
deposits of carbon in reduced (organic) form and of biological origin, including coal,
oil, natural gas, oil shales, and tar sands. A major concern is that they emit carbon
dioxide into the atmosphere when burnt, thus significantly
contributing to the enhanced greenhouse effect.
Fossil Fuel Combustion. Burning of coal, oil
(including gasoline), or natural gas. This burning, usually to generate energy, releases carbon
dioxide, as well as combustion by products that can include unburned hydrocarbons,
methane, and carbon monoxide. Carbon monoxide, methane, and many of the
unburned hydrocarbons slowly oxidize into carbon dioxide in the atmosphere. Common sources
of fossil fuel combustion include cars and electric utilities.
Framework Convention on Climate Change (). The landmark
international treaty unveiled at the United Nations Conference on Environment and
Development (UNCED, also known as the "Rio Summit"), in June 1992. The FCCC
commits signatory countries to stabilize anthropogenic (i.e.,
human-induced) greenhouse gas emissions to 'levels that would
prevent dangerous anthropogenic interference with the climate system'. The FCCC also
requires that all signatory parties develop and update national inventories of
anthropogenic emissions of all greenhouse gases not otherwise controlled by the Montreal
Protocol. Out of 155 countries that have ratified this accord, the U.S. was the
first industrialized nation to do so.
General Circulation Model (GCM). A global,
three-dimensional computer model of the climate system which can be used to simulate
human-induced climate change. GCMs are highly complex and they represent the effects of
such factors as reflective and absorptive properties of atmospheric water vapor,
greenhouse gas concentrations, clouds, annual and daily solar heating, ocean temperatures
and ice boundaries. The most recent GCMs include global representations of the atmosphere,
oceans, and land surface.
Geosphere. The soils, sediments, and rock layers of the
Earth's crust, both continental and beneath the ocean floors.
Global Warming. An increase in the near surface
temperature of the Earth. Global warming has occurred in the distant past as the result of
natural influences, but the term is most often used to refer to the warming predicted to
occur as a result of increased emissions of greenhouse gases. Scientists generally agree
that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years.
The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased
concentrations of greenhouse gases are causing an increase in the Earth's
surface temperature and that increased concentrations of sulfate aerosols have led to
relative cooling in some regions, generally over and downwind of heavily industrialized
areas. Also see Climate Change and Enhanced Greenhouse Effect.
Global Warming Potential (GWP). The index
used to translate the level of emissions of various gases into a common
measure in order to compare the relative radiative forcing of different
gases without directly calculating the changes in atmospheric concentrations. GWPs are
calculated as the ratio of the radiative forcing that would result from the
emissions of one kilogram of a greenhouse gas to that from emission of one
kilogram of carbon dioxide over a period of time (usually 100 years). Gases
involved in complex atmospheric chemical processes have not been assigned GWPs due to
complications that arise. Greenhouse gases are expressed in terms of Carbon Dioxide
Equivalent. The International Panel on Climate Change (IPCC) has
presented these GWPs and regularly updates them in new assessments. The chart below shows
the original GWPs (assigned in 1990) and the most recent GWPs (assigned in 1996) for the
most important greenhouse gases.
* Not Applicable. GWP was not yet estimated for this gas.
**This figure is an average GWP for the two PFCs, CF4 and C2F6.
Greenhouse Effect. The effect produced as greenhouse
gases allow incoming solar radiation to pass through the Earth's atmosphere,
but prevent most of the outgoing infra-red radiation from the surface and
lower atmosphere from escaping into outer space. This process occurs naturally and has
kept the Earth's temperature about 59 degrees F warmer than it would otherwise be. Current
life on Earth could not be sustained without the natural greenhouse effect.
Greenhouse Gas. Any gas that absorbs infra-red
radiation in the atmosphere. Greenhouse gases include water
vapor, carbon dioxide (CO2), methane (CH4),
nitrous oxide (N2O), halogenated fluorocarbons
(HCFCs) , ozone (O3), perfluorinated carbons
(PFCs), and hydrofluorocarbons (HFCs).
Halocarbons. Chemicals consisting of carbon, sometimes
hydrogen, and either chlorine, fluorine bromine or iodine.
Halons. These man-made substances (also known as
bromofluorocarbons) are chlorofluorocarbons that contain bromine. See also Chlorofluorocarbons
and Related Compounds.
Hydrocarbons. Substances containing only hydrogen and
carbon. Fossil fuels are made up of hydrocarbons. Some hydrocarbon compounds
are major air pollutants.
Hydrofluorocarbons (HFCs). These chemicals
(along with perfluorocarbons) were introduced as alternatives to ozone
depleting substances in serving many industrial, commercial, and personal needs.
HFCs are emitted as by-products of industrial processes and are also used in
manufacturing. They do not significantly deplete the stratospheric ozone
layer, but they are powerful greenhouse gases with global warming
potentials ranging from 140 (HFC-152a) to 12,100 (HFC-23).
Hydrosphere. The part of the Earth composed of water
including clouds, oceans, seas, ice caps, glaciers, lakes, rivers, underground water
supplies, and atmospheric water vapor.
Ice Core. A cylindrical section of ice removed from a glacier
or an ice sheet in order to study climate patterns of the past. By performing chemical
analyses on the air trapped in the ice, scientists can estimate the percentage of carbon
dioxide and other trace gases in the atmosphere at that time.
Infra-red Radiation. The heat energy that is emitted
from all solids, liquids, and gases. In the context of the greenhouse issue, the term
refers to the heat energy emitted by the Earth's surface and its atmosphere. Greenhouse
gases strongly absorb this radiation in the Earth's atmosphere,
and reradiate some back towards the surface, creating the greenhouse effect.
Intergovernmental Panel on Climate Change. The IPCC was
established jointly by the United Nations Environment Programme and the World
Meteorological Organization in 1988. The purpose of the IPCC is to assess information in
the scientific and technical literature related to all significant components of the issue
of climate change. The IPCC draws upon hundreds of the world's expert scientists as
authors and thousands as expert reviewers. Leading experts on climate change and
environmental, social, and economic sciences from some 60 nations have helped the IPCC to
prepare periodic assessments of the scientific underpinnings for understanding global
climate change and its consequences. With its capacity for reporting on climate change,
its consequences, and the viability of adaptation and mitigation measures, the IPCC is
also looked to as the official advisory body to the world's governments on the state of
the science of the climate change issue. For example, the IPCC organized the development
of internationally accepted methods for conducting national greenhouse gas emission
Joint Implementation. Agreements made between two or more
nations under the auspices of the Framework Convention on Climate Change to
help reduce greenhouse gas emissions.
Lifetime (Atmospheric). The lifetime of a greenhouse
gas refers to the approximate amount of time it would take for the anthropogenic
increment to an atmospheric pollutant concentration to return to its natural level
(assuming emissions cease) as a result of either being converted to another chemical
compound or being taken out of the atmosphere via a sink. This time depends
on the pollutant's sources and sinks as well as its reactivity. The lifetime of a
pollutant is often considered in conjunction with the mixing of pollutants in the
atmosphere; a long lifetime will allow the pollutant to mix throughout the atmosphere.
Average lifetimes can vary from about a week (sulfate aerosols) to more than a century
(CFCs, carbon dioxide).
Mauna Loa. A volcano on the island of Hawaii where
scientists have maintained the longest continuous collection of reliable daily atmospheric
Meteorology. The science of weather-related phenomena.
Methane (CH4). A hydrocarbon that
is a greenhouse gas with a global warming potential most
recently estimated at 24.5. Methane is produced through anaerobic (without oxygen)
decomposition of waste in landfills, animal digestion, decomposition of animal wastes,
production and distribution of natural gas and oil, coal production , and incomplete fossil
fuel combustion. The atmospheric concentration of methane has been shown to be
increasing at a rate of about 0.6% per year and the concentration of about 1.7 parts per
million by volume (ppmv) is more than twice its preindustrial value. However, the rate of
increase of methane in the atmosphere may be stabilizing.
Metric Ton. Common international measurement for the
quantity of greenhouse gas emissions. A metric ton is equal to 2205 lbs or 1.1 short
Mount Pinatubo. A volcano in the Philippine Islands that
erupted in 1991. The eruption of Mount Pinatubo ejected enough particulate
and sulfate aerosol matter into the atmosphere to block some
of the incoming solar radiation from reaching Earth's atmosphere. This
effectively cooled the planet from 1992 to 1994, masking the warming that had been
occurring for most of the 1980s and 1990s.
Nitrogen Oxides (NOx). Gases consisting of one molecule
of nitrogen and varying numbers of oxygen molecules. Nitrogen oxides are produced in the emissions
of vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can
contribute to formation of photochemical ozone (smog), can impair visibility, and have
health consequences; they are thus considered pollutants.
Nitrous Oxide (N2O). A powerful greenhouse
gas with a global warming potential of 320. Major sources of nitrous
oxide include soil cultivation practices, especially the use of commercial and organic
fertilizers, fossil fuel combustion, nitric acid production, and
Ozone (O3). Ozone consists of three atoms of
oxygen bonded together in contrast to normal atmospheric oxygen which consists of two
atoms of oxygen. Ozone is an important greenhouse gas found in both the stratosphere
(about 90% of the total atmospheric loading) and the troposphere (about
10%). Ozone has other effects beyond acting as a greenhouse gas. In the stratosphere,
ozone provides a protective layer shielding the Earth from ultraviolet radiation
and subsequent harmful health effect on humans and the environment. In the troposphere,
oxygen molecules in ozone combine with other chemicals and gases (oxidization) to cause
Particulates. Tiny pieces of solid or liquid matter,
such as soot, dust, fumes, or mist.
Perfluorocarbons (PFCs). A group of human-made
chemicals composed of carbon and fluorine only: CF4 and C2F6. These chemicals,
specifically CF4 and C2F6, (along with hydrofluorocarbons) were introduced
as alternatives to the ozone depleting substances. In addition, they are
emitted as by-products of industrial processes and are also used in manufacturing. PFCs do
not harm the stratospheric ozone layer, but they are powerful greenhouse
gases: CF4 has a global warming potential (GWP) of 6,300 and C2F6
has a GWP of 12,500.
Photosynthesis. The process by which green plants
use light to synthesize organic compounds from carbon dioxide and water. In
the process oxygen and water are released. Increased levels of carbon dioxide can increase
net photosynthesis in some plants. Plants create a very important reservoir for carbon
Pollutant. Strictly, too much of any substance in the
wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution
may be defined as the presence of substances in the atmosphere, resulting
from man-made activities or from natural processes that cause adverse effects to human
health, property, and the environment.
Precautionary Approach. The approach promoted under
the Framework Convention of Climate Change to help achieve stabilization of greenhouse
gas concentrations in the atmosphere at a level that would prevent
dangerous interference with the climate system.
Precession. The tendency of the Earth's axis to wobble
in space over a period of 23,000 years. The Earth's precession is one of the factors that
results in the planet receiving different amounts of solar energy over
extended periods of time.
Radiation. Energy emitted in the form of electromagnetic
waves. Radiation has differing characteristics depending upon the wavelength. Because the
radiation from the Sun is relatively energetic, it has a short wavelength (ultra-violet,
visible, and near infra-red) while energy re-radiated from the Earth's surface and the atmosphere
has a longer wavelength (infra-red radiation) because the Earth is cooler
than the Sun.
Radiative Forcing. A change in the balance between
incoming solar radiation and outgoing infra-red
radiation. Without any radiative forcing, solar radiation coming to the Earth
would continue to be approximately equal to the infra-red radiation emitted from the
Earth. The addition of greenhouse gases traps and increased fraction of the
infra-red radiation, reradiating it back toward the surface and creating a warming
influence (i.e., positive radiative forcing because incoming solar radiation will exceed
outgoing infra-red radiation).
Residence Time. The average time spent in a reservoir by
an individual atom or molecule. Also, the age of a molecule when it leaves the reservoir.
With respect to greenhouse gases, residence time usually refers to how long
a particular molecule remains in the atmosphere.
Respiration. The process by which animals use up
stored foods (by combustion with oxygen) to produce energy.
Short Ton. Common measurement for a ton in the United
States. A short ton is equal to 2,000 lbs or 0.907 metric tons.
Sink. A reservoir that uptakes a pollutant from
another part of its cycle. Soil and trees tend to act as natural sinks for carbon.
Solar Radiation. Energy from the Sun. Also referred to as
short-wave radiation. Of importance to the climate system, solar radiation includes
ultra-violet radiation, visible radiation, and infra-red radiation.
Stratosphere. The part of the atmosphere
directly above the troposphere. See Atmosphere.
Sulfate Aerosol. Particulate matter that
consists of compounds of sulfur formed by the interaction of sulfur dioxide
and sulfur trioxide with other compounds in the atmosphere. Sulfate aerosols
are injected into the atmosphere from the combustion of fossil fuels and the
eruption of volcanoes like Mt. Pinatubo. Recent theory suggests that sulfate
aerosols may lower the earth's temperature by reflecting away solar radiation
(negative radiative forcing). Global Climate Models which
incorporate the effects of sulfate aerosols more accurately predict global temperature
Sulfur Dioxide (SO2). A compound composed of one sulfur and
two oxygen molecules. Sulfur dioxide emitted into the atmosphere through
natural and anthropogenic processes is changed in a complex series of
chemical reactions in the atmosphere to sulfate aerosols. These aerosols
result in negative radiative forcing (i.e., tending to cool the Earth's
Sulfur Hexafluoride (SF6). A very powerful greenhouse
gas used primarily in electrical transmission and distribution systems. SF6 has a
global warming potential of 24,900.
Trace Gas. Any one of the less common gases found in the
Earth's atmosphere. Nitrogen, oxygen, and argon make up more than 99 percent
of the Earth's atmosphere. Other gases, such as carbon dioxide, water
vapor, methane, oxides of nitrogen, ozone, and ammonia, are
considered trace gases. Although relatively unimportant in terms of their absolute volume,
they have significant effects on the Earth's weather and climate.
Troposphere. The lowest layer of the atmosphere. The
troposphere extends from the Earth's surface up to about 10-15 km. See also Atmosphere.
Tropospheric Ozone (O3). Ozone that
is located in the troposphere and plays a significant role in the greenhouse
gas effect and urban smog. See Ozone for more details.
Tropospheric Ozone Precursor. Gases
that influence the rate at which ozone is created and destroyed in the
atmosphere. Such gases include: carbon monoxide (CO), nitrogen oxides (NOx),
and nonmethane volatile organic compounds (NMVOCs).
Water Vapor. The most abundant greenhouse gas,
it is the water present in the atmosphere in gaseous form. Water vapor is an
important part of the natural greenhouse effect. While humans are not
significantly increasing its concentration, it contributes to the enhanced
greenhouse effect because the warming influence of greenhouse gases leads to a
positive water vapor feedback. In addition to its role as a natural
greenhouse gas, water vapor plays an important role in regulating the temperature of the
planet because clouds form when excess water vapor in the atmosphere condenses to form ice
and water droplets and precipitation.
Weather. Weather is the specific condition of the
atmosphere at a particular place and time. It is measured in terms of such things as wind,
temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most
places, weather can change from hour-to-hour, day-to-day, and season-to-season. Climate
is the average of weather over time and space. A simple way of remembering the difference
is that 'climate' is what you expect (e.g., cold winters).