Download Climate Change-1: Greenhouse Effect and the Role of CO 1. What is

Climate Change-1:
Greenhouse Effect and the Role of CO2
CHEM/ENVS 380
1.  What is the greenhouse effect, and how does it work?
2.  What is the enhanced greenhouse effect? How is it different from the
greenhouse effect?
3.  What are the key chemical properties of greenhouse gases? Be able to
identify major greenhouse gases.
4.  Which greenhouse gas contributes the most to the greenhouse effect?
Enhanced greenhouse effect?
4.  What is the atmospheric window? What is its environmental significance?
5.  What happens to anthropogenic CO2 after emission into the atmosphere?
Some relevant topics from General Chemistry:
electromagnetic radiation, photons, wavelength
electronegativity, polar bonds, dipole and dipole moments
molecular vibrations, absorption spectra
Fig. 1. Time series of departures
from the 1961 to 1990 base period
for an annual mean global
temperature of 14.0°C (bars) and
for a carbon dioxide mean of 334
ppmv (solid curve) during the base
period, using data from ice cores
and (after 1958) from Mauna Loa
(4). The global average surface
heating approximates that of
carbon dioxide increases, because
of the cancellation of aerosols and
other greenhouse gas effects, but
this does not apply regionally (2).
Many other factors (such as the
effects of volcanic eruptions and
solar irradiance changes) are also
important.
Karl and Trenberth (2003) Modern global climate change, Science, 302: 1719-1723.
1963: Mt. Agung
1991 Mt. Pinatubo
Houghton JT et al. (2001) Climate Change 2001: The Scientific Basis, IPCC Third Assessment Report.
Houghton JT et al. (2001)
Climate Change 2001:
The Scientific Basis, IPCC
Third Assessment Report.
Tiny Bubbles Tell All, E. J. Brook.
References 2 and 3:
2. U. Siegenthaler et al.,
Science, 310, 1313 (2005).
3. R. Spahni et al., Science,
310, 1317 (2005).
Incoming Solar Radiation
•  Less than 1 billionth of the total energy emitted by the Sun is
intercepted by the Earth.
•  Fate of solar radiation reaching the Earth:
Absorbed at the
Earth’s surface
30 %
50 %
20 %
Reflected by
clouds, ice, snow,
etc. (albedo)
including
O3!
Absorbed by the
atmosphere (gases
and water droplets)
The Earth’s Annual Energy Balance
235 outgoing radiation
107
albedo
342 incoming radiation
67
195
window
The Atmosphere
324
168
40 atmospheric
Back Radiation
492 surface radiation +
convection + latent heat
The Earth’s Surface
At steady-state, incoming radiation = outgoing radiation.
Units: Watts m-2; after Beade et al. (2001) in IPCC Third Assessment Report, Houghton et al. eds.
Wavelengths of Incoming and Outgoing Radiation
UV
Baird (2003), 2nd ed., Fig. 4-1
VIS
IR
Thermal IR
Baird and Cann, Figure 1-6.
In order for an atmospheric gas
to function as a greenhouse
gas, in which region of the
electromagnetic spectrum must
the gas absorb?
For a gas to absorb in the IR....
• 
must be able to undergo internal vibrational motions
–  Stretching vibrations
–  Bending vibrations
• 
vibration must alter the dipole moment of the molecule
–  Dipole moment is a measure of asymmetry in charge distribution, and is
determined by the magnitude of the charge difference and the distance
between the two centers of charge
H2O
HF
http://www.chem.tamu.edu/organic/Spring99/
dipolemoments.html
CO2
Which of these gases absorb IR
due to internal vibrational motions? N2
H2
CCl4
H 2O
O2
CO
CH4
Ar
O3
N 2O
Which of these are greenhouse
gases? N2
H2
CCl4
H 2O
O2
CO
CH4
Ar
O3
N 2O
Salby S. (2012) Physics of the Atmosphere and Climate, Cambridge University Press.
“LW radiation”
refers to
radiation
emitted by the
Earth’s surface.
Gases in Remote Continental Areas
(from Spiro and Stigliani, 2003)
Constituent
Concentration (ppmv) Greenhouse Gas?
Nitrogen
N2
780,900
Oxygen
O2
209,400
Argon
Ar
9,300
Water (average)
H 2O
~4,000
Carbon Dioxide
CO2
370
Neon
Ne
18
Helium
He
5.2
Methane
CH4
1.7
Krypton
Kr
1.1
Hydrogen
H2
0.5
Nitrous Oxide
N 2O
0.3
Carbon Monoxide CO
0.04-0.08
Ozone
0.01-0.04
CFCs
O3
0.0002
Absorption
of Outgoing IR
by
H2O and CO2
Spiro and Stigliani (2003) Chemistry of the Environment, Prentice Hall
Water vapor contributes most to the GHE
responsible responsible
for
for GHE
enhanced
GHE
Sarmiento JL and Gruber N (2006) Ocean Biogeochemical Dynamics, Princeton University Press.