ATS150Introduction to Climate ChangeSpring 2010

Study Guide for Final Exam

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:

  1. Climates of the Past
  2. Geologic Time and Climates of the Distant Past
  3. Units: Ga (giga-annum) = billions of years ago; Ma (mega-annum) = millions of years ago; ka = thousands of years ago
  4. Earth formed from fragments ~ 4.7 Ga
  5. Sun was 30% dimmer, brightened steadily over time
  6. Early atmosphere was mostly CO2 and H2O, slowly depleted
  7. Massive rearrangements of continents changed climate by reorganizing ocean circulation
  8. Earth was warmer than today over most of geologic time
  9. Except for 3-4 glacial periods, usually no ice at all
  10. Massive impact ~ 65Ma killed dinosaurs (and much else)
  11. Slow cooling since 65 Ma: Antarctica to Pole, Southern Ocean
  12. Ice Age Climates (the past 2.5 million years)
  13. Ice sheets have come and gone ~20 x in past 2.5 Ma
  14. Ice sheets (and mountain glaciers) form when more snow falls in winter than can melt in summer
  15. Continental ice sheets take ~40-80 k years to build, ~10-20 k years to collapse and melt away
  16. Timing of ice ages (~100,000 years) driven by subtle changes in geometry of Earth’s orbit around the Sun
  17. Orbital changes (tilt, eccentricity, precession) modulate intensity of July Sun at 60 N
  18. Ice-albedo and carbon cycle feedback amplify these subtle changes to produce global ice ages @ ~ 100k years
  19. Last Glacial Maximum (LGM) ~ 18k years ago
  20. Last interglacial period ~ 125k years ago
  21. Since the Last Glacial Maximum
  22. Melting & warming abruptly reversed ~ 13ka by thermohaline collapse due to freshwater runoff into North Atlantic (“Younger Dryas”), plunged Europe back to Ice Age conds
  23. Warming led to “climatic optimum” ~ 6ka, then slow cooling
  24. Medieval Warm Period (1000 – 1200 AD) probably associated with enhanced solar activity (Vikings, Euro-Agriculture)
  25. Cooling into Little Ice Age (1600-1800 AD) associated with prolonged solar minimum and volcanic eruptions; Euro-famines, advancing mountain glaciers
  26. Rapid warming since ~ 1850, now warmer than Climatic Optimum ~6000 BP, probably warmest since last interglacial
  27. The Carbon Cycle
  28. Reservoirs and Fluxes of Carbon in the Earth System
  29. Units: 1 Billion Tons = 1 gigaton = 1 Gt = the mass of a cube of water 1 km on a side
  30. Reservoirs (“pools”): Atmosphere=775 GtC; Land Plants and Soils = 2000 GtC; Oceans = 38,000 GtC; Fossil Fuel = 4000 GtC
  31. Current global fossil fuel emissions = 8.4 GtC/yr
  32. Atmospheric CO2 increases by ~ 4 GtC/yr
  33. Oceans and land each take up ~ 2 GtC/yr
  34. Big changes from year to year (especially on land), probably related to climate fluctuations like El Nino
  35. 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)
  36. Ocean carbon uptake
  37. “Titration” of carbonic acid (H2CO3) into alkaline seawater slowly acidifies ocean (increasing H, decreasing pH), will eventually saturate when CO3 becomes limiting
  38. Rate of chemical reaction between atmospheric CO2 and seawater is limited by physical contact with deep ocean
  39. Warm water floats, cold water sinks, takes ~ 1000 years for deep ocean to be exposed to the atmosphere
  40. Nearly all fossil-fuel-derived CO2 in ocean is near surface
  41. Ocean “biological pump” takes some near-surface carbon to depth via sinking debris (dead plankton and poop)
  42. Reaction H2CO3 -> H+ + HCO3- -> H+ + CO32- steadily acidifies seawater, depletes CO3 and will eventually make CaCO3 dissolve (big problem for limestone, shellfish, corals)
  43. 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!
  44. Land carbon uptake
  45. Global photosynthesis ~100 GtC/yr converts more than 10x as much CO2 to organic matter as fossil fuel emits
  46. Global respiration, death, and decomposition pretty much balances global photosynthesis
  47. Small imbalance between growth and decay currently sequesters about 2 GtC/yr (about 25% of fossil emissions)
  48. Global land sink of CO2 means that worldwide, biosphere is growing faster than it’s dying! How is this possible?
  49. 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)
  50. Nutrient deposition & fertilizer application (both intentional and unintentional from dilute air pollution)
  51. Land-use change (reforestation, agricultural abandonment, forest fire suppression, & woody shrub invasion exceed carbon losses by deforestation and forest degradation worldwide?)
  52. Arctic warming (trees and shrubs growing where only tundra was able to survive before, leading to carbon storage)
  53. Coupled climate-carbon cycle prediction
  54. 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
  55. Current models disagree sharply about how much ocean sink will increase with rising atmospheric CO2 (chemistry)
  56. 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
  57. For a given level of assumed future fossil fuel emissions, models disagree by ~300 ppm on how much CO2 in 2100 !
  58. Fossil Fuel and Energy Economics:
  59. Distribution of emissions is very uneven
  60. Roughly 1/3 in USA, 1/3 in China, 1/3 in rest of the world (especially Europe)
  61. Emissions leveling off in Europe, increasing dramatically in China and (more slowly) in India
  62. Sources & uses of energy and CO2 emissions
  63. Globally, oil > coal > gas > nuclear > renewables
  64. USA: gets most from oil & gas; France gets most from nuclear; China & India get most from coal
  65. In USA roughly 1/3 for electricity (mostly coal), 1/3 for industry (coal & gas), 1/3 for transportation (mostly oil)
  66. Nearly all oil & gas reserves are in Middle East (& Russia), but nearly all oil & gas consumption is in USA & Europe
  67. Biggest coal reserves in USA, Russia, & China
  68. Peak Oil production, supply, and demand
  69. Historically, production of limited resources follows a “Bell curve” over time
  70. 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)
  71. Oil production in USA has fallen along Bell curve since 1970’s
  72. 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)
  73. When demand rises faster than supply, prices skyrocket
  74. Predicting future emissions: The Kaya Identity
  75. 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)
  76. Vast majority of world’s population is poor (low GDP per person), which keeps F much lower than otherwise!
  77. US, Europe have much higher GDP, but low emissions per $GDP
  78. As global economy develops, people become less poor (which is, of course, a good thing!)
  79. 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
  80. 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
  81. Estimating future emissions: IPCC Special Report on Emission Scenarios
  82. Starting around 1990, economists & demographers developed a suite of “scenarios” for future emissions, based on self-consistent “storyboards” of population, economic development, trade, technology, supply & demand, politics
  83. 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)
  84. Low-growth scenarios (B1, B2, etc) consider emissions leveling off at 8-15 GtC/yr by 2100 (maybe peaking about 2050)
  85. Stabilizing atmospheric CO2 at 450 ppm would require immediate reductions, halving global emissions by 2050
  86. Stabilizing at 650 ppm (compared to 390 now) would require emissions peak by 2040 ~12 GtC/yr, fall later
  87. Current emissions are well above even the fastest-growth scenarios considered by IPCC 15 years ago!
  1. Radiative Forcing of Climate Change
  2. Climate Forcing, Response, and Sensitivity
  3. 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)
  4. Without feedback, climate sensitivity is about 0.25 K per 1 Wm-2
  5. Predictable radiative forcing
  6. Greenhouse gases: about 4 Wm-2per doubling of CO2
    (only about 2 Wm-2today, comparedto 1800)
  7. 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
  8. Solar variability: 11-year solar cycle of 2-3 Wm-2from max to min
  9. Slower solar changes: maybe a decrease of 0.5 Wm-2from Medieval Warm Period (1300 AD) to Little Ice Age (1750)
  10. Huge volcanic eruptions (not little ones like Iceland in 2010), as much as 1.5 Wm-2for a couple of years due to stratospheric dust
  11. Current climate gets 2 – 2.5 Wm-2from enhanced greenhouse effect, offset by about 0.5 – 1 Wm-2due to pollution aerosols. Negligible amount (maybe 0.1 to 0.2 Wm-2) due to sun
  1. Climate Models
  2. “Back of an Envelope” Climate Models (Arrhenius, 1897)
  3. Predict global average temperature based on sunshine, albedo, and atmospheric emissivity using simple physics and algebra
  4. Estimate that without feedback, doubling CO2 would warm global average temperature by 1.2 °C
  5. 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
  6. 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!)
  7. Modern Climate Models
  8. Include as much physics as we can afford … feedbacks calculated as part of model rather than estimated, space/time resolved
  9. Components: Atmosphere, Ocean, Land-surface, Sea-ice
  10. Equations predict state of millions of “boxes” on a global grid every few minutes for centuries; boxes ~ 100 km on a side
  11. Simulations require huge computing costs
  12. Missing: Ice sheet flow! Cloud updrafts & rain/snow formation! Biological/ecological changes! Chemistry! Humans!
  13. Evaluation of Climate Model Accuracy
  14. Prediction of climate of 20th Century is quite good: trends, decadal fluctuations due to pollution, solar activity, volcanoes
  15. Recent observed trends in middle of predictions from 1990 era
  16. Correct prediction of warming near surface over continents, weaker warming over oceans, cooling in stratosphere
  17. Global temps quite good, regional errors of 1-3 °C common
  18. Prediction of pressure changes not bad, but not so good either
  19. Predictions of increasing water vapor (positive feedback), increased rainfall, changes in ocean temps very good
  20. Rainfall patterns quite good, regional errors near coastlines, mountain ranges quite bad (don’t believe local predictions!)
  21. 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)
  1. Projections of Future Climate
  2. How projections are made
  3. Get emissions scenarios from economists, use simple carbon cycle models (land, ocean, etc) to predict future levels of CO2 in air
  4. Use full-blown global climate models to predict changes in radiative forcing due to downward longwave radiation
  5. Use climate models to predict temp, pressure, humidity, rainfall, winds, etc that constitute feedback to radiative forcing
  6. What the projections say for the 21st Century
  7. CO2 levels reach 550 to 1000 ppm by 2100 (depending on which emission scenario comes true, of course!)
  8. Radiative forcing due to enhanced greenhouse gases reaches 4 to 9 W m-2 by 2100 (depends on emission scenario)
  9. Positive feedback (water vapor, high clouds, albedo) outweighs negative feedback (low clouds, vertical mixing)
  10. Best estimate global average warming of 1.5 to 4 °C by 2100 (depending on emission scenario)
  11. Probability distribution of about 2 to 8 °C average warming for high emissions scenario by 2100 (depending on model physics)
  12. Warming will not be uniform! Land > oceans; north > south; snowy places > warm places (ice albedo)
  13. Warming over central USA 2 – 6 °C (= 4 – 11 °F) depending on emissions scenario, with up to 15 °F average warming in Arctic!
  14. Changes in rainfall: wet places get wetter, dry places get drier (enhancement of Hadley Circulation), SW USA probably drier
  15. Much more evaporation, less soil moisture & runoff over USA and Western Europe, more soil water over Canada and Russia
  16. Dramatic losses of summer sea ice in both Arctic & Antarctic
  17. Possible slowdown of thermohaline circulation (not all models)
  18. More hot days, fewer cold days, longer growing seasons, less frost
  19. Steadily falling ocean pH, possible massive extinctions of calcium-shelled marine life by 2050-2070
  20. Sea-level rise of 25 to 60 cm by 2100 (but models don’t move ice!)
  21. The “Long Tail:” Long TermChanges in CO2 and Climate
  22. After fossil fuel emissions cease, CO2 will react with seawater for about 3000 years (3 times around the thermohaline loop)
  23. About 25% of all CO2 ever emitted still in the air in 5000 AD
  24. 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)
  25. Last 10% of fossil CO2 must slowly weather igneous rocks over 100,000’s of years!
  26. 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
  27. “Warming is logarithmic:” last CO2 to go away “counts the most”
  28. Fossil CO2 will warm the climate for 10’s of thousands of years!
  29. 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
  1. Climate Change Adaptation and Mitigation
  2. Impacts, Adaptation, and Emissions Reductions
  3. Impacts on water supply, heat waves, droughts, crops, food supply, ocean pH, fisheries likely to be quite severe
  4. Stabilizing CO2 at 450 ppm would be very difficult, requiring almost immediate reductions in rich countries, and reductions for everyone by 2025
  5. 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!
  6. Impacts on global politics, hunger, immigration, wars?
  7. Mitigation by emissions reduction
  8. CO2 budget of the air: 800 GtC today (400 at LGM, 600 in 1850)
  9. Current emissions about 8 GtC/yr, 2 GtC/yr to ocean & 2 GtC/yr into land (land may not be reliable in future)
  10. Define “Stabilization Triangle” as holding emissions steady for 50 years, putting off reductions for your grandchildren
  11. (Note stabilizing emissions does not stabilize CO2 or climate!!)
  12. Emissions Avoidance “Wedges” (Socolow & Pacala, 200x)
  13. Divide emissions triangle into 8 wedges, each growing a new technology or management method to replace 1 GtC/yr in 2060 (starts with nothing)
  14. 15 “wedges” described based on existing commercial (profitable) technologies (others like fusion or algae fuel don’t exist yet but may save our butts)
  15. At current market rates, each wedge is worth $2.5 trillion over 50 years (Wall Street bailout ~ War on Terror ~ 0.7 trillion)
  16. 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?

  1. How to pay for energy technology & climate mitigation
  2. “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
  3. 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!
  4. Just like First Industrial Revolution, this will not be mandated or paid for by governments
  5. Cost will equal the output of the entire world economy for many decades to come
  6. Socioeconomic consequences, benefits, changes in quality of life will be at least as profound as the 19th-20th Century changes
  7. “You’re Going to be OK!”

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