nitrous oxide (N 2 O), halogenated fluorocarbons (HCFCs), ozone (O 3 ),
perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs), water vapor, and
sulfur hexafluoride. Each of them and its related process or technologies are
discussed below.
3.1.1 Carbon Dioxide
Carbon dioxide is a naturally occurring gas and also a by-product of burning fossil
fuels and biomass, as well as land-use changes and other industrial processes. It is
the principal human-caused greenhouse gas that affects the earth’s radiative balance.
It is the reference gas against which other greenhouse gases are measured and
therefore has a global warming potential of 1.
Carbon dioxide’s ability to absorb heat is characterized by the molecular structure, the wavelength, and radiative properties. Visible light from the sun is able to
pass the carbon dioxide molecules without its energy being absorbed since the
frequency of visible light does induce a dipole moment on the atmospheric CO 2
molecules. Carbon dioxide does however absorb infrared radiation (heat from the
earth’s surface) and also reemits that energy at the same wavelength as what was
absorbed (also as heat) [6]. As for its molecular structure, “Carbon dioxide doesn’t
have a molecular dipole in its ground state. However, some CO 2 vibrations produce
a structure with a molecular dipole. Because of this, CO 2 strongly absorbs infrared
radiation.” [7]
On the electromagnetic spectrum, infrared lies in the range of 700 nm to 1 mm
(1000,000 nm). Carbon dioxide has absorption wave numbers of 667 cm
À1 and
2349 cm
À1 [11]. When converted to wavelengths, it is equal to ~15,000 nm
and ~ 4257 nm, respectively, and is well within the infrared range. Coincidently
15,000 nm also corresponds to the maximum intensity of the Planck function [6].
The energy of a molecule can change due to a change in the energy state of the
electrons of which it is composed. Thus, the molecule also has electronic energy.
The energy levels are quantized and take discrete values only. Absorption and
emission of radiation takes place when the atoms or molecules undergo transitions
from one energy state to another. In general, these transitions are governed by
selection rules. Atoms exhibit line spectra associated with electronic energy levels.
The dipole moment is determined by the magnitude of the charge difference and
the distance between the two centers of charge. If there is a match in frequency of the
radiation and the natural vibration of the molecule, absorption occurs and this alters
the amplitude of the molecular vibration. This also occurs when the rotation of
asymmetric molecules around their centers results in a dipole moment change, which
permits interaction with the radiation field. Dipole moment is a vector quantity and
depends on the orientation of the molecule and the photon electric vector [12].
Carbon dioxide equivalent is 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 (MMTCO 2 Eq).” The carbon dioxide equivalent for a
1 Effect of Global Warming and Climate Change on Glaciers and Salmons
5
perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs), water vapor, and
sulfur hexafluoride. Each of them and its related process or technologies are
discussed below.
3.1.1 Carbon Dioxide
Carbon dioxide is a naturally occurring gas and also a by-product of burning fossil
fuels and biomass, as well as land-use changes and other industrial processes. It is
the principal human-caused greenhouse gas that affects the earth’s radiative balance.
It is the reference gas against which other greenhouse gases are measured and
therefore has a global warming potential of 1.
Carbon dioxide’s ability to absorb heat is characterized by the molecular structure, the wavelength, and radiative properties. Visible light from the sun is able to
pass the carbon dioxide molecules without its energy being absorbed since the
frequency of visible light does induce a dipole moment on the atmospheric CO 2
molecules. Carbon dioxide does however absorb infrared radiation (heat from the
earth’s surface) and also reemits that energy at the same wavelength as what was
absorbed (also as heat) [6]. As for its molecular structure, “Carbon dioxide doesn’t
have a molecular dipole in its ground state. However, some CO 2 vibrations produce
a structure with a molecular dipole. Because of this, CO 2 strongly absorbs infrared
radiation.” [7]
On the electromagnetic spectrum, infrared lies in the range of 700 nm to 1 mm
(1000,000 nm). Carbon dioxide has absorption wave numbers of 667 cm
À1 and
2349 cm
À1 [11]. When converted to wavelengths, it is equal to ~15,000 nm
and ~ 4257 nm, respectively, and is well within the infrared range. Coincidently
15,000 nm also corresponds to the maximum intensity of the Planck function [6].
The energy of a molecule can change due to a change in the energy state of the
electrons of which it is composed. Thus, the molecule also has electronic energy.
The energy levels are quantized and take discrete values only. Absorption and
emission of radiation takes place when the atoms or molecules undergo transitions
from one energy state to another. In general, these transitions are governed by
selection rules. Atoms exhibit line spectra associated with electronic energy levels.
The dipole moment is determined by the magnitude of the charge difference and
the distance between the two centers of charge. If there is a match in frequency of the
radiation and the natural vibration of the molecule, absorption occurs and this alters
the amplitude of the molecular vibration. This also occurs when the rotation of
asymmetric molecules around their centers results in a dipole moment change, which
permits interaction with the radiation field. Dipole moment is a vector quantity and
depends on the orientation of the molecule and the photon electric vector [12].
Carbon dioxide equivalent is 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 (MMTCO 2 Eq).” The carbon dioxide equivalent for a
1 Effect of Global Warming and Climate Change on Glaciers and Salmons
5