ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
We’ll have the final exam in ATS 150 on Wednesday May 12 from 11:20 to 1:20, in
the regular classroom. The exam will count 25% of your grade for the course. You
will need to bring a pencil or pen to the exam, but you won’t need a “blue book.” The
format of the exam will be pretty much the same as the in-class exams.
I’m mainly trying to see that you understand concepts presented in the lectures. I
don’t want you to memorize a bunch of stuff from the notes or the textbook. The
exam will be “open notes,” meaning you can use printed copies of the lecture
notes, or books, or stuff you’ve written down during the exam. You may not
consult one another, or look stuff up on the internet. The exam will cover stuff we’ve
talked about in class. The textbook may or may not be helpful in studying (I hope
so), but I will not ask you anything on the exam that is in the book but has not
been covered in class. Also, there will be no calculations or math problems on
the exam.
The idea of this study guide is not to tell you precisely what questions will be on the
exam. Rather, I’m trying to tell you what topics from the class will be covered.
Basically, the exam covers all the lecture materials since the previous exam: “Past
Climates,” “Carbon Cycle,” “Fossil Energy,” “Radiative Forcing,” “Climate Models,”
“Future Climate,” and “Adaptation and Mitigation.”
Here’s a list of stuff to study:
I. Climates of the Past
a. Geologic Time and Climates of the Distant Past
 Units: Ga (giga-annum) = billions of years ago; Ma (megaannum) = millions of years ago; ka = thousands of years ago
 Earth formed from fragments ~ 4.7 Ga
 Sun was 30% dimmer, brightened steadily over time
 Early atmosphere was mostly CO2 and H2O, slowly depleted
 Massive rearrangements of continents changed climate by
reorganizing ocean circulation
 Earth was warmer than today over most of geologic time
 Except for 3-4 glacial periods, usually no ice at all
 Massive impact ~ 65Ma killed dinosaurs (and much else)
 Slow cooling since 65 Ma: Antarctica to Pole, Southern Ocean
b. Ice Age Climates (the past 2.5 million years)
 Ice sheets have come and gone ~20 x in past 2.5 Ma
 Ice sheets (and mountain glaciers) form when more snow falls
in winter than can melt in summer
 Continental ice sheets take ~40-80 k years to build, ~10-20 k
years to collapse and melt away
 Timing of ice ages (~100,000 years) driven by subtle changes
in geometry of Earth’s orbit around the Sun
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Orbital changes (tilt, eccentricity, precession) modulate
intensity of July Sun at 60 N
 Ice-albedo and carbon cycle feedback amplify these subtle
changes to produce global ice ages @ ~ 100k years
 Last Glacial Maximum (LGM) ~ 18k years ago
 Last interglacial period ~ 125k years ago
c. Since the Last Glacial Maximum
 Melting & warming abruptly reversed ~ 13ka by thermohaline
collapse due to freshwater runoff into North Atlantic
(“Younger Dryas”), plunged Europe back to Ice Age conds
 Warming led to “climatic optimum” ~ 6ka, then slow cooling
 Medieval Warm Period (1000 – 1200 AD) probably associated
with enhanced solar activity (Vikings, Euro-Agriculture)
 Cooling into Little Ice Age (1600-1800 AD) associated with
prolonged solar minimum and volcanic eruptions; Eurofamines, advancing mountain glaciers
 Rapid warming since ~ 1850, now warmer than Climatic
Optimum ~6000 BP, probably warmest since last interglacial
II. The Carbon Cycle
a. Reservoirs and Fluxes of Carbon in the Earth System
 Units: 1 Billion Tons = 1 gigaton = 1 Gt = the mass of a cube of
water 1 km on a side
 Reservoirs (“pools”): Atmosphere=775 GtC; Land Plants and
Soils = 2000 GtC; Oceans = 38,000 GtC; Fossil Fuel = 4000 GtC
 Current global fossil fuel emissions = 8.4 GtC/yr
 Atmospheric CO2 increases by ~ 4 GtC/yr
 Oceans and land each take up ~ 2 GtC/yr
 Big changes from year to year (especially on land), probably
related to climate fluctuations like El Nino
 One-way fluxes dwarf net exchanges! (more than 100 GtC/yr in
global photosynthesis & respiration/decomposition; more
than 60 GtC/yr uptake and release by oceans)
b. Ocean carbon uptake
 “Titration” of carbonic acid (H2CO3) into alkaline seawater
slowly acidifies ocean (increasing H, decreasing pH), will
eventually saturate when CO3 becomes limiting
 Rate of chemical reaction between atmospheric CO2 and
seawater is limited by physical contact with deep ocean
 Warm water floats, cold water sinks, takes ~ 1000 years for
deep ocean to be exposed to the atmosphere
 Nearly all fossil-fuel-derived CO2 in ocean is near surface
 Ocean “biological pump” takes some near-surface carbon to
depth via sinking debris (dead plankton and poop)
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Reaction H2CO3 -> H+ + HCO3- -> H+ + CO32- steadily acidifies
seawater, depletes CO3 and will eventually make CaCO3
dissolve (big problem for limestone, shellfish, corals)
 Ocean chemistry limits rate of uptake and eventual total
storage of fossil fuel-derived CO2: ~ 1/3 of fossil CO2 will
remain in atmosphere for geologic time!
c. Land carbon uptake
 Global photosynthesis ~100 GtC/yr converts more than 10x as
much CO2 to organic matter as fossil fuel emits
 Global respiration, death, and decomposition pretty much
balances global photosynthesis
 Small imbalance between growth and decay currently
sequesters about 2 GtC/yr (about 25% of fossil emissions)
 Global land sink of CO2 means that worldwide, biosphere is
growing faster than it’s dying! How is this possible?
 CO2 Fertilization (extra CO2 makes plants grow faster, but
then there’s more dead stuff to decay & plants need other
stuff too, like nutrients, water, growing season)
 Nutrient deposition & fertilizer application (both intentional
and unintentional from dilute air pollution)
 Land-use change (reforestation, agricultural abandonment,
forest fire suppression, & woody shrub invasion exceed
carbon losses by deforestation and forest degradation
worldwide?)
 Arctic warming (trees and shrubs growing where only tundra
was able to survive before, leading to carbon storage)
d. Coupled climate-carbon cycle prediction
 Instead of telling climate models how much CO2 will be in the
air in the future, try to predict CO2 from emissions using
models of plant growth, decay, marine biology, ocean
circulation and chemistry, etc
 Current models disagree sharply about how much ocean sink
will increase with rising atmospheric CO2 (chemistry)
 Even more disagreement about whether land sink will
strengthen, weaken, or even reverse sign and dump huge
amounts of CO2 back into the atmosphere by 2050
 For a given level of assumed future fossil fuel emissions,
models disagree by ~300 ppm on how much CO2 in 2100 !
III. Fossil Fuel and Energy Economics:
a. Distribution of emissions is very uneven
 Roughly 1/3 in USA, 1/3 in China, 1/3 in rest of the world
(especially Europe)
 Emissions leveling off in Europe, increasing dramatically in
China and (more slowly) in India
b. Sources & uses of energy and CO2 emissions
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Globally, oil > coal > gas > nuclear > renewables
 USA: gets most from oil & gas; France gets most from nuclear;
China & India get most from coal
 In USA roughly 1/3 for electricity (mostly coal), 1/3 for
industry (coal & gas), 1/3 for transportation (mostly oil)
 Nearly all oil & gas reserves are in Middle East (& Russia), but
nearly all oil & gas consumption is in USA & Europe
 Biggest coal reserves in USA, Russia, & China
c. Peak Oil production, supply, and demand
 Historically, production of limited resources follows a “Bell
curve” over time
 In the 1950’s, Hubbert fitted historical production of oil in USA
to a Bell curve and predicted US production would peak
around 1975 (correct, but oil shocks were complicated)
 Oil production in USA has fallen along Bell curve since 1970’s
 Using Hubbert’s Peak model for world production data
predicts peak around 2010 (not running out, just can’t
produce oil any faster than we are now)
 When demand rises faster than supply, prices skyrocket
d. Predicting future emissions: The Kaya Identity
 Emissions F = P x g x e x f
(where P = population, g = GDP per person, e = energy use
per dollar of GDP, f = carbon use per energy produced)
 Vast majority of world’s population is poor (low GDP per
person), which keeps F much lower than otherwise!
 US, Europe have much higher GDP, but low emissions per $GDP
 As global economy develops, people become less poor (which
is, of course, a good thing!)
 Global GDP per person is rising much faster than population
(good!), but energy use per $GDP is much higher in poor
countries (India, China) than rich countries
 Future emissions F likely to grow much faster than population
P, even if energy use in rich countries falls, unless dramatic
changes are made in terms e and f
e. Estimating future emissions: IPCC Special Report on Emission
Scenarios
 Starting around 1990, economists & demographers developed
a suite of “scenarios” for future emissions, based on selfconsistent “storyboards” of population, economic
development, trade, technology, supply & demand, politics
 High-growth scenarios (A1, A2, etc) consider rapid
devlopment, regional blocs, emissions increasing to 20-30
GtC/yr by 2100 (compared to 8.4 GtC/yr today)
 Low-growth scenarios (B1, B2, etc) consider emissions leveling
off at 8-15 GtC/yr by 2100 (maybe peaking about 2050)
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Stabilizing atmospheric CO2 at 450 ppm would require
immediate reductions, halving global emissions by 2050
 Stabilizing at 650 ppm (compared to 390 now) would require
emissions peak by 2040 ~12 GtC/yr, fall later
 Current emissions are well above even the fastest-growth
scenarios considered by IPCC 15 years ago!
IV. Radiative Forcing of Climate Change
a. Climate Forcing, Response, and Sensitivity
 Define climate sensitivity as strength of response (e.g., change
in surface temperature) for a given change in forcing (e.g.,
change in heating by solar radiation)
 Without feedback, climate sensitivity is about 0.25 K per 1 Wm-2
b. Predictable radiative forcing
 Greenhouse gases: about 4 Wm-2 per doubling of CO2
(only about 2 Wm-2 today, compared to 1800)
 Sulfate aerosol due to air pollution, maybe 2-4 Wm-2 regionally,
over polluted areas and downwind (US, Europe, China), both
directly reflecting sunlight and making clouds brighter
 Solar variability: 11-year solar cycle of 2-3 Wm-2 from max to min
 Slower solar changes: maybe a decrease of 0.5 Wm-2 from
Medieval Warm Period (1300 AD) to Little Ice Age (1750)
 Huge volcanic eruptions (not little ones like Iceland in 2010), as
much as 1.5 Wm-2 for a couple of years due to stratospheric dust
 Current climate gets 2 – 2.5 Wm-2 from enhanced greenhouse
effect, offset by about 0.5 – 1 Wm-2 due to pollution aerosols.
Negligible amount (maybe 0.1 to 0.2 Wm-2 ) due to sun
V. Climate Models
a. “Back of an Envelope” Climate Models (Arrhenius, 1897)
 Predict global average temperature based on sunshine, albedo,
and atmospheric emissivity using simple physics and algebra
 Estimate that without feedback, doubling CO2 would warm global
average temperature by 1.2 °C
 Feedback strength estimated from ice age climate: 5 °C colder
with 7 W m-2 less radiation (lower CO2, higher albedo), so
almost three times as sensitive as Arrhenius result alone
 So simple-back-of-the-envelope algebra suggests about 3.5 °C of
warming per doubling of CO2
(same as IPCC, but 110 years earlier!)
b. Modern Climate Models
 Include as much physics as we can afford … feedbacks calculated
as part of model rather than estimated, space/time resolved
 Components: Atmosphere, Ocean, Land-surface, Sea-ice
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Equations predict state of millions of “boxes” on a global grid
every few minutes for centuries; boxes ~ 100 km on a side
 Simulations require huge computing costs
 Missing: Ice sheet flow! Cloud updrafts & rain/snow formation!
Biological/ecological changes! Chemistry! Humans!
c. Evaluation of Climate Model Accuracy
 Prediction of climate of 20th Century is quite good: trends,
decadal fluctuations due to pollution, solar activity, volcanoes
 Recent observed trends in middle of predictions from 1990 era
 Correct prediction of warming near surface over continents,
weaker warming over oceans, cooling in stratosphere
 Global temps quite good, regional errors of 1-3 °C common
 Prediction of pressure changes not bad, but not so good either
 Predictions of increasing water vapor (positive feedback),
increased rainfall, changes in ocean temps very good
 Rainfall patterns quite good, regional errors near coastlines,
mountain ranges quite bad (don’t believe local predictions!)
 Predictions of loss of sea ice, melting land ice, rising sea levels
much weaker than real life (ice dynamics not included, so
models underestimate observed rate of climate changes)
VI. Projections of Future Climate
a. How projections are made
 Get emissions scenarios from economists, use simple carbon cycle
models (land, ocean, etc) to predict future levels of CO2 in air
 Use full-blown global climate models to predict changes in
radiative forcing due to downward longwave radiation
 Use climate models to predict temp, pressure, humidity, rainfall,
winds, etc that constitute feedback to radiative forcing
b. What the projections say for the 21st Century
 CO2 levels reach 550 to 1000 ppm by 2100 (depending on which
emission scenario comes true, of course!)
 Radiative forcing due to enhanced greenhouse gases reaches 4 to
9 W m-2 by 2100 (depends on emission scenario)
 Positive feedback (water vapor, high clouds, albedo) outweighs
negative feedback (low clouds, vertical mixing)
 Best estimate global average warming of 1.5 to 4 °C by 2100
(depending on emission scenario)
 Probability distribution of about 2 to 8 °C average warming for
high emissions scenario by 2100 (depending on model physics)
 Warming will not be uniform! Land >> oceans; north >> south;
snowy places >> warm places (ice albedo)
 Warming over central USA 2 – 6 °C (= 4 – 11 °F) depending on
emissions scenario, with up to 15 °F average warming in Arctic!
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
 Changes in rainfall: wet places get wetter, dry places get drier
(enhancement of Hadley Circulation), SW USA probably drier
 Much more evaporation, less soil moisture & runoff over USA and
Western Europe, more soil water over Canada and Russia
 Dramatic losses of summer sea ice in both Arctic & Antarctic
 Possible slowdown of thermohaline circulation (not all models)
 More hot days, fewer cold days, longer growing seasons, less frost
 Steadily falling ocean pH, possible massive extinctions of calciumshelled marine life by 2050-2070
 Sea-level rise of 25 to 60 cm by 2100 (but models don’t move ice!)
c. The “Long Tail:” Long Term Changes in CO2 and Climate
 After fossil fuel emissions cease, CO2 will react with seawater for
about 3000 years (3 times around the thermohaline loop)
 About 25% of all CO2 ever emitted still in the air in 5000 AD
 Slower reaction with limestone for the next 20,000 years leaves
about 10% of all CO2 ever emitted in 25,000 AD (maybe still
450 ppm if we quit fossil emissions by 2200)
 Last 10% of fossil CO2 must slowly weather igneous rocks over
100,000’s of years!
 Lesson from the past: Big slug of CO2 emitted 55 Ma ago took
100,000 years to go away, warmed oceans for 100,000 years
 “Warming is logarithmic:” last CO2 to go away “counts the most”
 Fossil CO2 will warm the climate for 10’s of thousands of years!
 If sea levels in future behave as they did for past climate changes,
eventual response will be more than 50 m (160 feet!) of sea rise
VII.
Climate Change Adaptation and Mitigation
a. Impacts, Adaptation, and Emissions Reductions
 Impacts on water supply, heat waves, droughts, crops, food
supply, ocean pH, fisheries likely to be quite severe
 Stabilizing CO2 at 450 ppm would be very difficult, requiring
almost immediate reductions in rich countries, and
reductions for everyone by 2025
 Problem is not so much population or even consumption by
rich countries … hardest problem is how to lift billions of
people out of poverty while drastically cutting emissions!
 Impacts on global politics, hunger, immigration, wars?
b. Mitigation by emissions reduction
 CO2 budget of the air: 800 GtC today (400 at LGM, 600 in 1850)
 Current emissions about 8 GtC/yr, 2 GtC/yr to ocean & 2
GtC/yr into land (land may not be reliable in future)
 Define “Stabilization Triangle” as holding emissions steady for
50 years, putting off reductions for your grandchildren
 (Note stabilizing emissions does not stabilize CO2 or climate!!)
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ATS 150
Introduction to Climate Change
Study Guide for Final Exam
Spring 2010
c. Emissions Avoidance “Wedges” (Socolow & Pacala, 200x)
 Divide emissions triangle into 8 wedges, each growing a new
technology or management method to replace 1 GtC/yr in
2060 (starts with nothing)
 15 “wedges” described based on existing commercial
(profitable) technologies (others like fusion or algae fuel
don’t exist yet but may save our butts)
 At current market rates, each wedge is worth $2.5 trillion over
50 years (Wall Street bailout ~ War on Terror ~ 0.7 trillion)
 Energy efficiency & conservation (cheapest; negative costs!)
Double global gas mileage = 1 wedge
Compact fluorescent lighting ~ 0.25 wedge
Green buildings: 1 to 2 wedges
 Renewable energy like wind and solar (expensive but doable)
700 times current solar PV = 1 wedge
30 times current wind (1 million turbines) = 1 wedge
 Fuel switching, carbon capture & sequestration (CCS)
(most expensive but being pushed hardest)
Build 1400 gas electric plants instead of coal = 1 wedge
“Clean Coal:” Industrial CCS at power plants (replace 800
coal plants = 1 wedge)
 Nuclear power
Triple current nuclear power = 1 wedge
Return to 1970’s rate for 50 years = 1 wedge
Problems with waste disposal, terrorism?
d. How to pay for energy technology & climate mitigation
 “Intuitive” solutions will not suffice (use less, ride bikes, eat
vegan, grow gardens, build mass transit) because of need to
lift billions of people from poverty while eliminating
emissions
 Solving carbon/climate/energy problem will require nothing
short of a Second Industrial Revolution that replaces our
entire energy/economic system with one that can support
billions of people without emitting any CO2 at all!
 Just like First Industrial Revolution, this will not be mandated
or paid for by governments
 Cost will equal the output of the entire world economy for
many decades to come
 Socioeconomic consequences, benefits, changes in quality of
life will be at least as profound as the 19th-20th Century
changes
 “You’re Going to be OK!”
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