Download ATM S 211 Final Examination June 4, 2007 Name This examination

ATM S 211
Final Examination
June 4, 2007
Name _______________________________________
This examination consists of a total of 100 points. In each of the first two sections,
you have a choice of which questions to answer. Please note that you will not get
extra credit by answering more. You must answer all of the last three questions. If
you need more room, feel free to use the back side of the paper. If you do so,
however, indicate clearly which answer is being continued.
Briefly define any 6 of the following 8 terms (actually #8 is a multiple choice question!),
showing that you understand its meaning in the context of this course. You may give examples,
equations, and/or sketches if you think it is helpful. [4 points each, maximum of 24]
1. Catalyst (as it relates to stratospheric ozone chemistry)
A substance (atom, molecule or particle) that increases the rate of a chemical reaction but is
itself unchanged by the reaction.
2. Scattering (as it relates to radiation and the atmosphere)
The redirection of the path of a photon (or light ray) by particles or molecules in its path. Photons may
be scattered in any direction, including straight ahead.
3. Biological pump
The transfer of CO2 and nutrients from the surface waters to the deep ocean as a result of
photosynthesis in shallow waters, settling into the deep waters, and then decomposition
4. Radiative forcing
Change in energy flux into the surface-troposphere system due to a perturbation or change
in some component of the climate system
5. Internal variability of the climate system
Natural oscillations in the climate system caused by non-linear coupling among the various
components of the climate system, such as the ocean and atmosphere (ENSO). This variability arises
independently of any changes in external forcing.
6. Planetary albedo
The fraction of the incident solar radiation that is reflected back to space by a planet. This
reflection may be due to the atmosphere (molecules, clouds, aerosol) or the surface or both.
7. Milankovitch cycles
The periodic changes in the earth orbital parameters (eccentricity, obliquity, and precession)
that lead to variations in the solar radiation received by earth as a function of time.
8. Circle the correct answer: The ozone hole over Antarctica is a result of global warming.
True
False
Debatable
Answer any 5 of the following 6 short questions. [8 points each; maximum of 40]
1. The Antarctic ozone hole is caused by a combination of meteorology and chemistry. Explain
how each of these factors contributes to the ozone hole.
The meteorology of the Southern Hemisphere winter creates an intense symmetric
circulation (vortex) around the SH polar region that prevents horizontal transport of heat
into the region. Because the air continues to cool via thermal radiation, the vortex becomes
very cold, leading to the formation of small nitric acid ice particles.
The ice particles serve as a catalyst creating a large pool of Cl molecules. When the sun
returns, the molecules are split by photons producing a large number of Cl atoms that
rapidly delete the ozone. This process only stops when the vortex breaks down and warmer
air containing additional ozone is advected to the pole.
2. Identify and draw a system diagram for one positive feedback loop and one negative
feedback loop that operates within the Earth's climate system. Label your loops clearly. How
can one tell which one is negative and which one is positive?
Positive feedback: ice-albedo feedback
Negative feedback: silicate weathering
Count the number of negative couplings – if the
number is an odd number, the loop is negative; if the
number is even (or zero), the loop is positive
3. Climate change over the next century has been described as the “wet gets wetter and the dry
gets dryer”. What does this mean and what feature of the atmospheric circulation will
change to make this happen?
Climate models suggest that already climatologically dry areas will become dryer while
already wet areas will become wetter. The primary cause of this is an intensification of the
Hadley circulation. The cells penetrate further poleward, leading to an expanded subtropical
dry zone and reduced moisture. At the same time, the convergence zone becomes more
intense leading to more precipitation there. A similar intensification of precipitation occurs
in the mid-latitudes due to warmer, moister air masses.
4. What changes in snowpack and streamflow do we expect in the Pacific Northwest due to
rising temperatures? Give two examples of how segments of our economy could be affected
by these changes.
We expect that the snowpack will be reduced in amount and the streamflows will peak
earlier in the spring/summer than they currently do.
Segments that may be affected include
• Fishing (salmon)
• Forestry
• Tourism
• Power generation
• Agriculture
5. Explain how aerosols that arise following volcanic eruptions affect climate. Include where in
the atmosphere they can be found, how they interact with radiation, and how long they
persist.
Volcanic eruptions produce dust aerosol that typically is removed from the atmosphere
relatively rapidly and SO2 gas. When injected into the stratosphere, the SO2 gas combines
with water to produce stratospheric sulfate aerosol particles over a period of months. These
particles can then last in the stratosphere for periods of one to several years. The SO2
particles reflect solar radiation, thereby cooling down the earth-atmosphere system.
6. If we want to stabilize atmospheric CO2 concentrations, what has to happen to
anthropogenic emissions? Describe 3 technological options that can help achieve this goal of
stabilization.
In order to stabilize emissions, all anthropogenic emissions must cease. [not just be reduced,
but actually stop]. Among options to help achieve this goal are:
• Conservation – home insulation, use of energy efficient appliances etc.
• Improved fuel efficiency of cars and trucks
• Use of renewable power – biofuels, solar, wind, tides, etc.
• Use of nuclear power
• CO2 capture and storage
Answer each of the following three questions. Each one is worth 12 points. [Total of 36]
1. Answer the following global warming questions,
•
Approximately how much (in °C) has the earth warmed over the last 100 to 150 years?
What measurements are used to assess this warming?
•
Cite two other changes in the earth system that support climate warming.
•
How does the temperature warming over the last century compare to temperature
changes over the last 1000 years? What do we use to reconstruct temperature records
over the last 1000 years? (Give one or two examples.)
•
Is the warming caused by humans? Cite evidence to support your answer.
•
List two possible impacts that could result as average surface temperatures increase.
Earth has warmed about 0.8 °C over the past 100-150 years
Melting of land glaciers, increase in length of growing season, sea level rise, bore hole
temperatures
The recent rise in temperature (last 25 years and last 10 in particular) has pushed the surface
air temperature higher than at any time in the last 1000 years. The current rise is more than
3 standard deviations above that expected by random fluctuations
Yes. Evidence is the rise in greenhouse concentrations such as CO2, N2O and CH4, all
produced by human activity. Also IPCC summary reports.
Impacts
Enhanced droughts in the dry areas of the northern hemisphere
Flooding in mid latitudes due to increased precipitation
Expansion of the sub-tropical dry areas
Sea level rise due to thermal expansion
Melting of a major piece of the Greenland Ice Sheet leading to catastrophic sea level rise
Ocean acidification
2. The present atmosphere contains approximately 790 Gt (C) in the form of CO2, thus the
atmospheric CO2 concentration is about 380 ppmv. Assume that the Earth's total
recoverable fossil fuel reserves (mostly as coal) are 4800 Gt (C). At present, about half the
CO2 produced by the burning of fossil fuels stays in the atmosphere. The other half
dissolves in the oceans or is taken up by the terrestrial biosphere.
•
If this ratio of ½ remained constant and we burned up all of our fossil fuel reserves, by
how much would the atmospheric CO2 concentration rise? (Express your answers in
terms of the new CO2 level divided by the old one.)
The pre-industrial atmospheric CO2 concentration was about 285 ppmv. Climate models
suggest that doubling that concentration to about 550 ppmv will raise the global mean
surface temperature by about 3 °C.
•
Assuming that the same linear relationship exists between the atmospheric CO2
concentration and temperature, how much would the global mean surface temperature
be expected to rise given the concentration obtained above? (You will need to convert
your answer to the first part of this question to a value in ppmv.)
•
If the current rate of fossil fuel use is raising the atmospheric CO2 concentration at the
rate of 3.5 ppmv/year, how many years will it take us to reach a concentration of 550
ppmv?
•
Do you expect this rate of 3.5 ppmv per year to stay the same or increase with time?
Why?
New atmospheric burden of C after burning all the fossil fuel is
790 + ½ (4800) = 3190 Gt(C)
The ratio of new to old is 3190 / 790 = 4.0
New atmospheric concentration is then 4 x (380) = 1,520 ppmv
Linear rate of temperature rise is 3 C / (550 – 285 ppmv) = 0.011 C/ppmv
Temperature rise going from 285 to 1520 is (1520 – 285) ppmv x 0.011 C/ppmv = 13.6 C
Time to reach 550 ppmv is (550 – 380) ppmv / (3.5 ppmv/year) = 49 years
We expect the rate of 3.5 ppmv / year to actually increase unless real steps to mitigate fossil
fuel use are taken. More people using more energy will increase the annual rate of
production of CO2.
3. Draw two separate diagrams of the energy flow into the earth system from top of atmosphere
through the atmosphere to the surface and then out of the system.
•
Label the processes in your diagrams clearly.
•
If 100 units of solar energy enter the top of atmosphere, what happens to this energy in
the earth system?
•
Indicate the greenhouse effect in your diagram
Of the 100 units incident on the earth, 30 units are reflected back to space, 45 are
absorbed at the surface and 25 are absorbed in the atmosphere.
The greenhouse effect (the downward emission from the atmosphere is labeled in the
diagram.