For 10/28/09
From the book:
Chapter 3: 1, 2, 5, 7, 8, 12, 13, 14, 15, 16, 19, 23, 28, 30, 34, 35, 39, 47.
Appendix E of the text has answers to even numbered questions
1. (1) changes in solar radiation reaching the Earth (changes in the Sun’s output or the
Earth’s orbit), (2) changes in the fraction of solar radiation that is reflected (albedo), and
(3) changes in the infrared radiation that is radiated back into space.
5. CO2, CH4, H2O, N2O, halocarbons (Freons, CFCs)
7. Analysis of air trapped in samples of ancient ice at the polar caps.
13. In order to absorb IR radiation, a molecule must undergo a net change in dipole
moment as a result of its vibrational or rotational motion. IR radiation causes most
polyatomic molecules, including greenhouse gases H2O, CH4, and N2O, to vibrate and
absorb IR radiation. Methane has C-H bonds that absorb IR radiation in the 3000 cm-1
and 1250 cm-1 regions. CO2 has C=O bonds that absorb at about 2300 cm-1.
15. You must assume steady state (sources = sinks). Lifetime = reservoir/sinks (flux), so
reservoir = lifetime x flux = 100yr x 5x108kg yr-1 = 5x1010 kg. 5x1010kg (1000g/1kg)
(1mol/62g) = 8.06x1011mol. To find the mixing ratio divide by the total moles of the
atmosphere: (8.06x1011mol/1.8x1020mol) x 109 = 4.5ppbv
19. Carbon dioxide from burning this coal would increase the concentration of CO2 in
the atmosphere and it would act as a green house gas and cause more energy from the sun
to be captured in the atmosphere. The sulfate clouds produced from the sulfur in the coal
are highly reflective and would reflect more incoming light from the sun and would act in
an opposite way to CO2 to reduce the amount of energy in the atmosphere.
23. a) As the greenhouse effect raises the temperature of the Earth, the rate of
anaerobic decay in swamps would increase and thus more methane would be released. In
turn, the additional methane in the atmosphere would absorb IR radiation and itself cause
a further rise in temperature
b) There are large quantities of methane trapped at the bottom of the oceans as
methane-hydrate, which has the formula CH4.6H2O. Greenhouse warming of the oceans,
which extended to their bottoms, could cause the release of methane from methanehydrate.
c) There is the possibility that these positive feedback mechanisms could combine to
release large amounts of methane that would begin a runaway greenhouse effect that
would threaten all life on Earth.
35. Volcanic eruptions and changes in solar output. Solar output is always important.
Currently, there are very few volcanically derived sulfur aerosols in the stratosphere.
39. Mile-long ice cores, dating back 160,000 years, were taken from Antarctic glaciers
and the air trapped in pockets in the ice was analyzed for carbon dioxide. They also
estimated the air temperature at the time the air became locked in the ice, using a
technique based on measurements of the ratio of deuterium (21H) to ordinary hydrogen
(11H) in the ice surrounding the air pockets. Lighter water molecules evaporate more
readily than heavy water molecules. Therefore, the higher the 21H/11H ratio in the frozen
water, the higher the temperature. From their findings, the scientists were able to estimate
temperatures at the time the different layers of ice were formed.
47. Fertilizing the ocean surface with iron sulfate will allow marine phytoplankton to
reproduce more rapidly and remove even more CO2. Although laboratory-scale iron
fertilization experiments have verified that Fe is a limiting nutrient, its effect is shortlived, and the amount of new production exported from the surface layer is small. In
addition, this approach would require continuous seeding of vast areas with outrageous
amounts of Fe, which may cause unknown harm to existing marine ecosystems.
Other Problems:
Assume the average composition of fossil fuel is CH1.6.
How many moles of O2 are used up for every mole of fossil fuel burned?
CH1.6 + 1.4O2 → CO2 + 0.8H2O
How many moles of O2 are produced for every mole of CO2 sequestered via
photosynthesis?
One mole of O2 is produced per one mole of CO2 taken up by photosynthesis.
Is any O2 produced when CO2 dissolves into the ocean?
No. CO2 dissolving into the ocean is a purely physical process and no chemistry occurs.
Over a 3 year period, global CO2 increased by 3.2 ppmv and global O2 decreased by 8.8
ppmv. Global fossil fuel consumption during this period was 6.3x1012 kg C yr-1.
Assuming that fossil fuel consumption was the only thing affecting CO2 and O2
concentrations, by how much should CO2 and O2 mixing ratios have changed?
The atmosphere contains 1.8x1020 moles of air.
3 x 6.3x1012 kg C yr-1 = 18.9x1012 kg C = 1.6x1015moles of CO2. Divide by 1.8x1020
moles of air and get 8.9ppmv increase in CO2. Multiply this by 1.4 (stoichiometry from
above) and get a 12.4ppmv decrease in O2.
From the observations, determine what fraction of CO2 carbon emitted from
burning fossil fuels ended up in the biosphere, the oceans, and the atmosphere.
The difference between the observed and expected change in O2 is due to uptake of CO2
by the biosphere through photosynthesis (12.4 – 8.8 = 3.6ppmv). From the stoichiometry
for photosynthesis this equates to 3.6ppmv of CO2 taken up by the biosphere which is
40% of the CO2 emitted. The remainder of the difference in the expected and observed
CO2 must be due to the ocean (8.9 – 3.6 = 5.3; and 5.3 – 3.2 = 2.1ppmv went to the
ocean) Therefore, 24% dissolved into the ocean, and the remaining 36% accumulated in
the atmosphere.
The solar constant for Mars is 594 Wm-2 and it has an albedo of 0.15. What is the black
body temperature of Mars? The surface temperature of Mars is 220 K. What can you
conclude about the Martian atmosphere?
πr2F(1-A) = 4πr2σT4, so 594Wm-2(1-0.15) = 4(5.67x10-8Wm-2K-4)T4, solve for T to get
217K. This is close to the actual surface temperature, which means that Mars does not
have a very strong greenhouse affect.
Why does the loss of ozone in the stratosphere result in stratospheric cooling and
tropospheric warming?
The absorption of ultraviolet light in the stratosphere is a main source of heat to the
stratosphere, so loss of ozone should lead to cooling of the stratosphere. The increased
amount of radiation reaching the Earth's surface should cause a net increase in the amount
of heat contained in the troposphere.
List two positive climate feedbacks, and two negative climate feedbacks.
Positive:
As temperature increases, water vapor in the atmosphere increases, which causes a
further increase in temperature.
As temperature increases, polar ice melts, which reveals ocean water below. The ocean
water has a lower albedo than the ice and therefore, less solar radiation is reflected back
to space. This results in further heating.
Negative:
As water vapor in the atmosphere increases due to higher temperatures, more clouds
form, which reflect solar radiation back to space increasing the Earth's albedo. The
reduction in solar radiation leads to cooling.
As CO2 concentrations increase leading to higher temperatures, both the higher
temperatures and increased CO2 lead to greater rates of photosynthesis in the biosphere.
The uptake of CO2 leads to lower atmospheric concentrations and negative forcing
leading to cooling.
How could radiative forcing due to CO2 emitted from volcanoes over thousands of years
bring the Earth out of an ice age, but not lead to global warming during an interglacial
period?
During an ice age the CO2 from volcanoes will accumulate in the atmosphere over a long
period of time and lead to warming, which could lead to ice melt. During an interglacial
period, the CO2 emitted would be absorbed by the ocean and would not accumulated in
the atmosphere, therefore less warming would be expected due to the volcanic emissions.
The key here is that the emission of CO2 from the volcanoes is slow enough for the ocean
to keep up.
Why does anthropogenic radiative forcing due to the cloud albedo effect have the highest
uncertainties with respect to other sources of anthropogenic radiative forcing?
Clouds are a natural phenomenon, and trying to determine the fraction of cloud cover that
is due to anthropogenic activities is not simple. The issue is compounded due to the fact
that the chain of events that occur between the emission of an anthropogenic aerosol and
cloud formation is very complicated and currently poorly understood.
Also review previous questions regarding the carbon cycle.