Geog 372 Global Climate Change


Second Midterm Study Guide

First Midterm Thursday, Oct. 1, Stv. 3036

Exam and Explanations

The first midterm will consist of ten multiple choice questions (1 pt each), ten short answer questions (3 pts each) and one short essay (10 pts). The short answer questions should be answered briefly, with a few words or phrases, and possibly a sketch. You will have several choices of topic for the short essay question, and will answer it in one or two short paragraphs for a total of no more than one page of text. You may also want to use a sketch or diagram to illustrate your essay. This midterm will cover Ruddiman, Chapters 1-4. You should also look at the 1st edition Chapter 2 of Ruddiman on line for review of modern climate.


Multiple Choice. Choose the best answer if more than one appears correct. Read each answer carefully. (1 pt each)

1. Which of the following is NOT a major control on climate distribution from place to place?
a. general atmospheric circulation
b. continentality, distribution of continental masses and relief
c. proximity to water, especially oceans
d. tectonic activity
e. elevation and topography

2. The shape and depth of ocean basins are controlled by ______ and influence rates of _______ .
a. rates of sea floor spreading; carbon dioxide emissions by volcanoes
b. continental drift; rock weathering
c. tectonic uplift; sea surface temperature change
d. wandering of the poles; sea level change
e. sea floor spreading and continental drift; carbon dioxide released to atmosphere and sea level change.

Short Answer. Answer each with a few words or phrases or brief paragraph. Include diagrams where helpful or requested. (3 pts)

1.What are the three independent forcing mechanisms that cause climate change over time? Describe each briefly.

Short Essay. Write an essay in one or two paragraphs, using full sentences and proper grammar and spelling. Use diagrams where useful. Be sure to answer all parts of the question. (10 pts) FOR THE EXAM, I WILL PICK ONE OF THE FOLLOWING ESSAY PROMPTS. You can prepare outlines of each in order to be prepared to answer any of these questions on the exam.

A. Why are accurate dating methods important to the reconstruction of past climate? What kinds of assumptions must be made when using and interpreting different dating methods? Which dating methods are most precise and which are less precise? Use examples of different dating methods to illustrate your answer.

B. Discuss the range of proxy indicators used to reconstruct past climate. What are the characteristics of a good proxy for climate? Why, and in what ways, is vegetation a good proxy for climate? What sorts of proxy information can be obtained from lake sediments and shorelines? What sorts of proxy information can be obtained from ocean sediments and shorelines?

C. Discuss the role of feedbacks, both positive and negative, in climate change over long time periods. Include a discussion of variations in solar intensity, tectonic change, atmospheric chemistry (particularly CO2). How do weathering rates and vegetation respond and thus play a role in these feedbacks? What role does the ocean play?


The following topics and concepts will be covered on the first midterm.

How to study: go over your notes carefully, review illustrations in the text, re-read portions of the text that are not clear, ask questions of your fellow students and Prof Freidel, via email or in class.

Climate -- basic processes

See Fig. 1-5, page 9, Ruddiman, be able to discuss
Climate forcing -- tectonic, orbital variations, solar radiation variations, anthropogenic
Response to forcing (see Table 1.1, page 12), fast, slow
Feedbacks: Positive (reinforces and amplifies change); Negative (suppresses change, reduces response)
Uniformitarianism -- Present is key to the past; past is the key to the future

Solar radiation as driving force for general atmospheric circulation
Energy balance of earth (See Fig. 2-3, page 20, Ruddiman)
incoming shortwave (solar, insolation)
portions reflected, scattered, absorbed (by what?)
outgoing long wave (heat) radiation
portions absorbed and reradiated (by what?)

Earth’s albedo, albedo of different surfaces (high or low) (Table 2-1, p. 23)
Albedo-temperature feedback, positive when ice forming, positive when ice melting

Electromagnetic spectrum
compare earth and solar energy outputs
radiation laws re wavelength, energy emitted, energy intercepted with distance

Latitudinal differences in energy --
Differences in solar angle (angle of incidence)
low latitudes - high energy input -- surplus
high latitudes - low energy input -- deficit
Energy transported from surplus to deficit areas by ocean currents, winds,
Latent heat storage and release during evaporation and condensation

Controls on climate distribution from place to place
General atmospheric circulation
continental masses, distribution and relief
ocean circulation, shape and size of ocean basins
thermohaline circulation
cold water upwelling
elevation and topography
surface cover, vegetation

Hydrologic cycle

Greenhouse effect
Gasses in the atmosphere that absorb outgoing longwave radiation
CO 2, H 2O, CH 4, N­ 2O.
About 50% of Incoming solar radiation passes through atmosphere without absorption; about 20% is absorbed by clouds and atmosphere
Total of about 70% of insolation heats surface and atmosphere; 30% is earth's albedo
Outgoing Longwave energy (heat) is recycled by clouds, absorbing gases,
reradiated back toward earth’s surface and radiated out to space

Carbon cycle, sources of CO2 storage and release

Evidence of past climate
Proxy indicators -- (be able to define term)
Dendroclimatology -- tree rings
Fossil vegetation --
pollen -- how collected, interpreted
plant assemblages
plant macrofossils -- especially in
packrat middens -- where found, how preserved, etc.
lake levels of closed-basin lakes, water balance proportional to climate change
lake varves
ice cores
marine cores, plankton, forams, radiolarian, diatoms
Stratigraphic layers -- relative age
Stratigraphic markers -- tephras (volcanic ash)

Dating methods
Numerical dating methods--
Instrumental, back to a couple of hundred years, poorly distributed globally
Also annual layers: tree rings (dendrochronology), sediment varves, ice layers, corals
Radiometric -- based on breakdown of isotopes, radioactive decay
Halflife -- what does this mean? Useful dating period for each isotope
Types of material dated for each isotope -- e.g. organics by C-14
Radiocarbon (C-14 into N-14)
Uranium series; Potassium-Argon;
Cosmogenic isotopes -- C-14, also Cl-36 in rocks
Relative and Correlative Dating methods--
Tephrachronology -- id tephras by oxides of elements
Paleomagnetism -- correlate variations in earth's magnetic field over time, place to place

Climate Models
Physical climate models -- 1-D, 2-D, 3-D Global Circulation Models (GCMs)
Purposes, resolution, time periods

History of climate fluctuations through time
Range of time scales (see Figure1.2 and 1.3 pages 5-6, Ruddiman)
Do not memorize dates, but focus on patterns of climate variations through time
e.g. major glaciations lasting several million years every several hundred million year periods (not cyclic)
Know names, terms, geologic time periods:
Quaternary (last ~1.6 my),
Pleistocene (ice age, 1.6 my-10,000 C-14 yr BP),
Wisconsinan glaciation (~80,000-10,000 yrs BP),
Eemian, last interglacial, (~125,000 yrs BP)
Holocene (last 10 ky),

Possible Causes of past climate fluctuations -- on range of time scales, long term to short term
Continental drift (distribution of continents at high or low latitudes, scattered or concentrated)
Mountain building (orographic precipitation, change in atmospheric circulation, weathering)
Weathering, chemical (See Fig. 3-21, p. 70)
Changes in ocean circulation patterns
Changes in CO2 in atmosphere and oceans
Orbital parameters (briefly)--
eccentricity of orbit-- circular to elliptical -- ~100,000 year cycle
tilt of earth's axis -- ~21.5 to 24.5 degrees -- 41,000 year cycle
Precession of equinoxes: timing of perihelion and aphelion -- ~23,000 yr cycle
Changes in solar output -- sun spots, or lack of sun spots
random: meteor strikes, volcanic eruptions (short term)

Tectonic Scale Climate Change, Carbon Cycle
The greenhouse effect -- Why is Venus so hot while the Earth has maintained a more moderate temperature?
The Faint Young Sun Paradox -- what could have allowed the earth to maintain a moderate temperature over the past 4 plus billion years despite the fact that the sun was about 30% cooler during the earliest billion or two?
Evolution of the Earth's atmosphere through time
Carbon cycle -- what are the sources of carbon dioxide in the atmosphere? What can cause carbon dioxide percentages to vary throughout Earth's history?
Carbon exchanges between rocks and the atmosphere --- how does CO2 get removed from the atmosphere? How is it put back into the atmosphere? What are the various residence times for CO2 in rocks, deep ocean, surface ocean, vegetation, atmosphere?
Chemical weathering -- role in CO2 balance in rocks, atmosphere; role in climate variations over long periods of time
Relationship between rates of tectonic uplift, sea floor spreading, global and latitudinal climate, and rates of chemical weathering as a response
Gaia Hypothesis -- What is the basic hypothesis? Does the earth have a thermostat of feedbacks that keeps the Earth's temperature and climate in balance over time, despite changes in solar output, changes in rates of tectonic activity, and changes in earth's orbital parameters? What is the role that the biosphere might play in this hypothesis? What was the role of primitive life forms 3.5 billion years ago in creating a more habitable environment for life to thrive on Earth?
Snowball Earth? Is there good evidence that the Earth went through a phase in which much or all of the planet was frozen over?

Plate Tectonics and Long Term Climate Change
Basics of plate tectonics -- oceanic (basaltic) and continental (granitic) masses, differences in rock densities;
Tectonic deformation -- earthquakes, faults, volcanoes -- distribution relative to plate boundaries
Convergent plate margins -- ocean trenches, island arcs of volcanoes, high mountain ranges, uplifted plateaus, etc.
Divergent plate margins -- oceanic spreading zones, rift zones on continents
Paleomagnetism -- global patterns, especially in ocean floor spreading zones -- magnetic reversals provide evidence of plate movement through time; oldest sea floors no more than ~170 million yrs old -- why?
Hypotheses regarding role of plate tectonics in climate change through time:
Polar position of Continents -- influence on glaciations? Gondwana glaciation as evidence, or not?
Pangaea -- supercontinent as cause of glaciation, or not? Why or why not? evidence versus models?
Tectonic control of CO2 in the atmosphere, oceans? -- Sea floor spreading rates as control on CO2? Fast seafloor spreading versus Slow seafloor spreading? How could this cause changes in global climate?
Uplift weathering as a cause of glaciations? What is the ultimate cause of such weathering? Weathering as both forcing and feedback?

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