# Global Warming I: The Science and Modeling of Climate Change Quiz Answers

### Global Warming I: The Science and Modeling of Climate Change Quiz Answers

#### Quiz 1: Optional Problems: How Much Coal to Run a Light Bulb

Q1. A joule is an amount of energy, and a watt is a rate of using energy, defined as 1 W = 1 J / s. How many joules of energy are required to run a 100 W light bulb for one day? Save your answer for use in the next question.

`Enter answer here`

Q2. Coal has about 30E6 J of energy per kg, but a power plant can only use 30% of this energy to make electricity (i.e., it is 30% efficient). How many kilograms of coal have to be burned to light a 100 W light bulb for one day?

`Enter answer here`

#### Quiz 2: Optional Problems: Comparing Energy Prices

Q1. You’re going to calculate the prices of a range of energy sources in common units of megaJoules of energy (equal to a million Joules) per dollar.

These questions should all be approached using the factor-label method, in which you write out explicitly the way that the units (inches, Joules, horses, miles per hour, whatever) combine to get the units you’re looking for. In this series of questions, you are looking for a number with units of megaJoules / \$. You are going to do 5 calculations, then marvel at your answers prompted by 3 multiple choice questions. Keep notes of your answers as you go through so you will be ready for that.

A gallon of gasoline carries with it about 1.3E8 Joules of energy. If you pay \$5 per gallon, how many megaJoules can you get for a dollar?

`Enter answer here`

Q2. Electricity goes for about \$0.05 per kilowatt hour. A kilowatt hour is just a weird way to write Joules, since a Watt is a Joule per second, and a kilowatt hour is the number of Joules one would get from running 1000 Watts times one hour (3600 seconds). In the form of electricity, how many megaJoules can you get for a dollar?

`Enter answer here`

Q3. A standard cubic foot of natural gas carries with it about 1.1 x 106 Joules of energy. You can get about 5 x 105 BTU’s of gas for a dollar, and there are about 1030 BTU’s in a standard cubic foot. How many megaJoules of energy in the form of natural gas can you get for a dollar?

`Enter answer here`

Q4. A ton of coal holds about 3.2 x 1010 Joules of energy, and costs about \$40. How many megaJoules of energy in the form of coal can you get for a dollar?

`Enter answer here`

Q5. Corn oil (biodiesel) costs about \$0.10 per fluid ounce wholesale. A fluid ounce carries about 240 dietary calories (which a scientist would call kilocalories). A calorie is about 4.2 Joules. How many megaJoules of energy in the form of corn oil can you get for a dollar?

`Enter answer here`

Q6. What is the ratio of the cost of the most expensive form of energy (in \$/MJ, not MJ/\$) to the cost of the cheapest form?

Q7. Which is the cheapest form of energy on your list?

• coal
• oil
• natural gas
• electricitiy
• biodiesel

Q8. Which is the most expensive?

• coal
• oil
• natural gas
• electricity
• biodiesel

#### Quiz 1: Optional Layer Model Problem: How Hot is the Moon?

Q1. The layer model assumes that the temperature of the body in space is all the same. This isn’t really very accurate, as you know that it’s colder at the poles than it is at the equator. For a bare rock with no atmosphere or ocean, like the moon, the situation is even worse, because fluids like air and water are how heat is carried around on the planet. So let’s make the other extreme assumption, that there is no heat transport on a bare rock like the moon. Assume for comparability that the albedo of this world is 0.33, and the solar constant is 1350 Watts/m2, same as for Earth.

What would be the equilibrium temperature of the surface of the moon, where influx equals outflux, on the equator, at local noon, when the sun is directly overhead, in Kelvins?

`Enter answer here`

Q2. What would be the equilibrium temperature, where energy outflow equals energy inflow, on the moon at night, in Kelvins?

`Enter answer here`

#### Quiz 2: Optional Layer Model Problem 2: A Stronger Greenhouse Effect

Q1. A two-layer model. Insert another atmospheric layer into the model, just like the first one. As you work through this exercise, keep track of your results because you will be comparing them to each other (like temperatures of different layers).

The layers are transparent to visible light but blackbodies in the infrared. First identify which arrow represents the incoming energy flux to the planet.

• a
• b
• c
• d
• e
• f

Q2. Now choose the right way to calculate the incoming energy flux, in Watts/m2 averaged over the Earth’s surface.

• L(1-alpha)/4
• ε σ T(ground)4
• ε σ T(layer 1)4
• ε σ T(layer 2)4

Q3. Which arrow represents outgoing energy lost from the planet to space?

• a
• b
• c
• d
• e
• f

Q4. How would you calculate how much energy is leaving the planet, in Watts/m2?

• L(1-alpha)/4
• ε σ T(ground)4
• ε σ T(layer 1)4
• ε σ T(layer 2)4

Q5. By setting the incoming and outgoing energy fluxes that you picked out equal to each other, we can write that L (1-α) / 4 = ε σ T(layer 2)4. This equation can be used to find the temperature of the skin layer, which is

• the ground
• layer 1
• layer 2

Q6. By setting the incoming and outgoing energy fluxes that you picked out equal to each other, we can write that L (1-α) / 4 = ε σ T(layer 2)4. Use a value of L of 1350 W/m2, α of 30%, ε = 1, and σ = 5.67 x 10-8 W/(m2 K4). Numerically, what is the value of the temperature of Layer 2, in Kelvins?

`Enter answer here`

Q7. Find the temperature of the next layer down, Atmosphere Layer 1, using a budget for atmospheric layer 2. Which arrow represents the incoming energy to layer 2?

• a
• b
• c
• d
• e
• f

Q8. What is the energy flux to Layer 2?

• L(1-α)/4
• ε σ T(ground)4
• ε σ T(layer 1)4
• ε σ T(layer 2)4

Q9. So you’ve found that ε σ T(Layer 1)4 = 2 * ε σ T(Layer 2)4. Rearrange this to find how much warmer Layer 1 is than Layer 2, the value of T(Layer 1) / T(Layer 2). Express your answer numerically, e.g. 3.14

`Enter answer here`

Q10. Now use the energy budget for Layer 1 in a similar way to calculate the temperature of the ground (Earth). What is the ratio of T(Earth) / T(Layer 2)?

`Enter answer here`

Q11. Analytically, the ratio of T(Earth) / T(skin)

• 2
• 21/2
• 21/4
• 31/4

#### Quiz 3: Optional Layer Model Problem 3: Nuclear Winter

Q1. Nuclear Winter. Go back to the 1-layer model, but change it so that the atmospheric layer absorbs visible light rather than allowing to pass through.

This could happen if the upper atmosphere were filled with dust. For simplicity, assume that the albedo of the earth remains at 30%, even though in the real world it might change with a dusty atmosphere. What is the ratio of T(Earth) / T(Atmosphere) in this case?

`Enter answer here`

#### Quiz 4: Quiz 1

Q1. If you double the kinetic energy of the atoms in an object, its temperature

• goes up by a factor of 16
• remains the same
• halves
• doubles

Q2. The amount of heat energy that an object holds is proportional to

• T4
• T2

the temperature, T

Q3. A photon of light with a high frequency has a __ wavelength

• short
• long

Q4. A valid formula for wavenumber (units of cycles / cm or just cm-1) is

• ν / c
• c / ν
• none of these
• c λ
• c / λ

Q5. Joules are to quarts of water as Watts are to

• gallons
• quarts per gallon
• quarts per second
• water pressure

Q6. What we feel as heat is the energy stored in

• formation of chemical bonds
• electron orbitals
• motion

Q7. A blackbody shines less energy than an object which is not a blackbody.

• FALSE
• TRUE

Q8. The greenhouse effect works by changing the energy flowing as

• visible light
• clouds
• infrared light
• water vapor

Q9. The formula for the bare-rock layer model for a planetary temperature is L (1-α) / 4 = ε σ T4. The factor of ε arises from

• whether the planet is a blackbody
• geometry
• the strength of the sun
• the behavior of visible light
• clouds and ice

Q10. What are the units of L?

• W/(m2 K4)
• unitless
• W/(m2 K)
• K
• W/m2

Q11. What if the Earth were a two-sided discworld, a flat circle with the sun perpetually directly overhead of one side. Let’s allow heat to conduct from the warm side to the cold side, so that the two sides have the same temperature. The temperature of either side would be governed by

• L (1-α) = 4 ε σ T4
• L (1-α) = ε σ T4
• L (1-α) = 2 ε σ T4

#### Quiz 1: Model Greenhouse Gases in the Atmosphere

Q1. Answer these questions using the Modtran on-line model here. The model takes CO2 concentration and other environmental variables as input, and calculates the outgoing IR light spectrum to space. The total energy flux from all IR light is listed as part of the model output. You can compare the results from 2 separate runs by clicking “Save This Run to Background”

Which has a larger impact on the outgoing IR energy flux in Watts / m2, a 5 ppm increase in CO2 or a 5 ppm increase in methane (CH4), beginning from present-day values of 400 and 1.7 ppm?

• CO2
• CH4

Q2. Does a doubling of the atmospheric methane concentration have a larger or smaller impact on climate than a doubling of CO2?

• larger
• smaller

Q3. By varying the concentration of CH4, figure out where CH4 absorbs IR light. Which labeled region is it?

• a
• b
• c
• d
• e

Q4. How much CH4 (in ppm, just give a number) does it take before the absorption band begins to saturate like CO2? You’ll have to use your judgement to decide when the CH4 absorption band approaches the coldest Planck curve on the plot.

`Enter answer here`

Q5. What is the “equivalent CO2” of doubling atmospheric methane? That is to say, how many ppm of CO2, starting from the present-day value of 400 ppm, would lead to the same change in outgoing IR radiation energy flux as doubling methane? Type in the total amount of CO2 required in ppm, just the number.Enter answer here

`Enter answer here`

Q6. From the last problem, what is the ratio of the ppm change in CO2 to the ppm change in CH4? Assume that the concentrations of CO2 and CH4 start at their present-day values of 400 ppm and 1.7 ppm, respectively.

`Enter answer here`

#### Quiz 1: Model the Lapse Rate and Greenhouse Effect

Q1. In this quiz, we will use the RRTM Earth’s Energy Model. Instructions for using this model are available on the doc page by clicking on “how to”.

Go to the Earth’s Energy model. This model estimates the balance of energy flowing in and out of the Earth given certain conditions of the Sun, surface, and atmosphere. The values for the surface and atmosphere are assumed to be uniform across the whole Earth, and the fluxes (the arrows) are calculated as averages.

First, set up the model with an isothermal atmosphere by setting the Lapse Rate (temperature change with altitude) to 0. Check the total outgoing longwave radiation (OLR) by hovering on the blue up arrow. It should be ~372 W/m2. Now, let’s see how things change when we change the CO2 concentration in the atmosphere. Double the CO2 concentration to 800 ppm. Hover over the blue arrow to see the new value for outgoing longwave radiation.

How much has the OLR changed? Type in the difference in W/m2 between the old and new value below. Think about why this might be the case.

`Enter answer here`

Q2. Now, without changing the value of CO2, let’s give our atmosphere a nonuniform temperature profile. We’ll do so by turning up the lapse rate from 0 K/km to 10 K/km, about the value you would get from dry convection. This gives our model atmosphere a troposphere with declining temperatures up to a stratosphere at 15 km. Now look at the outgoing longwave radiation (the value when you hover on the blue up arrowhead). About how much less, in W/m2 is the OLR at the top of the atmosphere than it was before? Think about why this answer might be different than above, and notice what happens to IR radiation from the atmosphere as it passes through Earth’s atmosphere.

`Enter answer here`

Q3. Now adjust the Earth’s Surface Temperature to bring the Earth back into energy balance. Note that when you change the surface temperature, you’re also changing the temperature of the atmosphere, which is determined according to the surface temperature and the lapse rate. By about how many degrees K do you have to increase the surface temperature to balance the Earth’s energy budget?

`Enter answer here`

Q4. When an atmosphere is saturated with water, it follows the moist adiabat instead. Set the CO2 concentration back to 400 ppm. Set the lapse rate to 5 K/km, which is typical for a moist adiabat, and adjust the temperature to regain balance. Double the CO2 concentration, and find the new temperature at which the energy fluxes balance. By how many degrees K do you have to change surface temperature (relative to before you doubled CO2 in this question) to regain equilibrium? If you had to increase the temperature, put a positive number; otherwise, put a negative number.

`Enter answer here`

Q5. When a column of air gets warmer, its H2O concentration typically increases. This has two effects: it adds water, a greenhouse gas, to the column, which behaves much like CO2 did in question 2. This is known as the water vapor feedback. It also makes the lapse rate smaller, as occurred in question 4. This is known as the lapse rate feedback. A positive feedback is a consequence of global warming that leads to further warming, and a negative feedback is a consequence of global warming that lessens the amount of warming.

Given this, which describes the two feedbacks?

• The lapse rate feedback is positive and the water vapor feedback is negative.
• Both the water vapor and lapse rate feedbacks are negative feedbacks.
• Both the water vapor and lapse rate feedbacks are positive feedbacks.
• The water vapor feedback is a positive feedback and the lapse rate feedback is a negative feedback.

#### Quiz 1: Quiz 2

Q1. Select each gas that can absorb and emit IR light by interaction with its vibration, among the following

• Argon, Ar
• Chlorine, Cl2
• evaporated gasoline, say C6H14
• OH, a reactive radical compound in the atmosphere

Q2. The CO2 asymmetric stretch vibration is

• infrared active
• infrared inactive

Q3. Which of these differs most from the other two in terms of its emissivity, epsilon?

• ice
• liquid water
• water vapor

Q4. As a rule, a gas absorbs IR light if its vibrational frequency more-or-less matches the light’s frequency.

• false
• true

Q5. Water vapor is a blackbody.

• false
• true

Q6. Increasing the greenhouse gas concentration of the atmosphere makes the skin altitude

• move lower
• stay the same
• move higher

Q7. The band saturation effect tends to amplify the climate impact of a gas at

• low concentration
• high concentration

Q8. Which of the following is more band-saturated?

• a trace gas
• an abundant gas

Q9. The change in pressure with altitude in the atmosphere is a __ function.

• linear
• increasing exponential
• Gaussian
• decreasing exponential

Q10. The mixing ratio (concentration) of a long-lived gas like CO2 or O2 in the air _ with altitude in a well-mixed column

• decreases
• increases
• stays the same

Q11. A function relating pressure in a column of compressible fluid to height will be _.

• nonlinear
• linear

Q12. When you expand a gas without adding heat from outside (that is, adiabatically), condensation of water vapor in the gas

• releases heat
• absorbs heat

#### Quiz 1: Model Sunlight, Albedo, and Climate

Q1. In this quiz, we will use the RRTM Earth’s Energy Model. Instructions for using this model are available on the doc page by clicking on “how to”. Please note that for all numeric questions, just enter the amount without the units (e.g. put “100” and not “100 K”).

Go to the page for the Earth’s Energy Model. If our Sun is anything like similar stars we observe, it has been getting slowly brighter for most of Earth’s history. Current estimates hold that four billion years ago, in the Earth’s infancy, the Sun was only 75% as bright as it is today, so the direct sunlight received by the Earth was only 75% of the current quantity of ~1370 W/m2. Suppose the Sun suddenly reverted to this previous brightness. Adjust the Direct Sunlight input parameter accordingly. This should reduce the amount of shortwave radiation coming in from the sun, while leaving the longwave radiation unchanged. Confirm this by watching the arrows change when you adjust this value.

With this lower value of Direct Sunlight, how much more energy, in W/m2, is the Earth radiating to space than receiving from the sun? (Remember to type in just the number, without units.)

`Enter answer here`

Q2. With this lower level of sunlight, the Earth is losing energy, and so would gradually cool until the incoming and outgoing energy fluxes are in balance once more. Let’s determine the Earth’s new surface temperature in this scenario.

Set the atmospheric Lapse Rate to 0 K/km, and adjust the Earth’s Surface Temperature until the Earth is neither gaining nor losing energy. What is the Earth’s new equilibrium temperature, in K?

`Enter answer here`

Q3. Set the Direct Sunlight parameter back to 1370 W/m2, leaving the lapse rate at 0 K / km. Now, imagine that all the clouds and continents of our model planet disappear, leaving the Earth covered in ocean. We can model this changing the Surface parameter to Ocean (in the drop-down menu). Notice that this reduces the albedo of the Earth; also, notice which arrows change as a result. Using the same procedure as in Question 2, figure out and type in the Earth’s new equilibrium temperature in this scenario.

`Enter answer here`

Q4. Notice that the answer to the above question was below freezing. Change the surface from ocean to ice. Notice whether the Earth is now gaining or losing energy and think about why this would be so. What temperature do you have to set it to in order to restore the balance? It’s worth noting that geologists now believe that such “Snowball Earth” states have likely occurred in Earth’s distant past.

`Enter answer here`

Q5. If the temperature you found in Question 3 is above the freezing point of water, then the Earth will remain covered in ocean (remember that in our simplified model, the Earth’s surface is uniform); if it’s below the freezing point, then the state is unstable, and the Earth will freeze over, changing the energy balance. Similarly, if the temperature you find in Question 4 is below the freezing point of water, then the Earth will stay completely frozen over; otherwise, the state is unstable, and it will melt, changing the energy balance.

For the isothermal atmosphere you have been modeling in Questions 1-4, which of the states are stable?

• Both the ocean and ice states are stable (Earth’s water could be either frozen or unfrozen, depending on its initial state).
• The ocean state is stable, but the ice state is unstable (Earth’s ice would melt).
• The ice state is stable, but the ocean state is unstable (Earth’s water would freeze, covering the surface with ice).
• Both the ocean and ice states are unstable (the energy would not balance in either state).

Q6. Perform the same experiment as in Questions 3 and 4, but with a Lapse Rate of 6 K/km. Under these conditions, which states are stable and which are unstable?

• The ice state is stable, but the ocean state is unstable (Earth’s water would freeze, covering the surface with ice).
• Both the ocean and ice states are unstable (the energy would not balance in either state).
• The ocean state is stable, but the ice state is unstable (Earth’s ice would melt).
• Both the ocean and ice states are stable (Earth’s water could be either frozen or unfrozen, depending on its initial state).

#### Quiz 2: Extract the Water Vapor Feedback from Climate Model Results

Q1. Bring up the AR5 Model Mapper page.

Using at least three models, make maps of the Specific Humidity at an atmospheric pressure of 20,000 Pa (an input box that pops up when you select Specific Humidity). Make maps of the years 2000 and 2099. You will find that the colors are not very revealing, because the color scale extends to the kinds of high water vapor concentrations you find near the Earth’s surface. So fix the color scales using the Zoom color scale button.

In general (among the different years and models), the highest water vapor concentrations are found in the __.

• subtropical storm regions
• tropics
• polar regions

Q2. Now Calculate Anomalies for the data you downloaded for Question 1. You may have to toggle the Color Scales button a few times to see the results vividly. If you see positive anomalies in your maps, that means that there has been a positive water vapor feedback in the models. You can see the actual values of the anomalies by clicking on the map. For any of your 3 models, is the specific humidity lower in 2099 than in 2000?

• yes
• no

Q3. The strongest changes in Specific Humidity between the years 2000 and 2099 occur in

• polar regions
• temperate regions
• tropical regions

#### Quiz 3: Model Clouds 1: IR

Q1. In this short exercise, you’ll get to play with the MODTRAN model, which shows you what the frequency spectrum looks like for IR light emitted and absorbed by Earth and its atmosphere.

For questions that ask you to compare two model runs, you may find the Save to Background button useful.

Start up the MODTRAN model. Where in the spectrum do you see the biggest changes when you add clouds?

• c
• d
• b
• a
• e

Q2. For each cloud type that specifies the altitudes of the bottoms and tops of the clouds, run the model and note the outgoing IR flux in units of Watts / m2. Record the cloud name, the cloud base altitude, the cloud top altitude, and the outgoing IR flux for each of these types. Make 2 graphs: one of the outgoing IR flux against cloud base altitude, and one of the outgoing IR flux against cloud top altitude. Which altitude (base or top) gives a more linear graph?

• cloud top altitude
• cloud base altitude

Q3. Set the Sensor Altitude to 0 km, and choose the Looking Up option. Do this first with no clouds. The model shows the infrared light spectrum coming down from the sky. Get rid of water vapor by setting the Water Vapor Scale value to 0 (zero). You still see a lot of IR energy coming down from the sky. Where is it coming from? (You may have to play with some of the model’s parameters to figure this out).

• the sun
• clouds
• CO2
• outer space

#### Quiz 4: Model Clouds 2: Full-spectrum

Q1. In this quiz, we will use the RRTM Earth’s Energy Model. Instructions for using this model are available on the doc page, under “How To.” Remember, for all numeric questions, type in your answer without the units (e.g. put “100” and not “100 K”).

Bring up the RRTM model in its default settings.

Note the total outgoing reflected sunlight and longwave radiation, which you can find by hovering on the up-pointing orange and blue arrowheads, respectively. To get the energy flux to space, which is what we’re really after, hover the mouse on the arrowhead above the x-axis.

We want to compare the impacts of typical changes in cloud cover at high and low altitudes on outgoing sunlight (orange arrow) and IR (blue arrow). Make a table with these energy fluxes for (1) no clouds, (2) a low cloud fraction of 0.5 (50%), and (3) 50% low clouds and a high cloud fraction of 0.1 (10%).

What is the change, in W/m2, in reflected sunlight (outgoing shortwave radiation, i.e. the orange “up” arrowhead) due to the addition of low clouds? If it is higher with clouds, type in a positive number; if it is higher with no clouds, type in a negative number.

`Enter answer here`

Q2. Continuing Question 1, what is the change in outgoing longwave radiation due to the addition of 50% low clouds? Again, if it is higher with clouds, type in a positive number; if it is higher with no clouds, type in a negative number.

`Enter answer here`

Q3. What’s the difference in upward visible energy flux (reflected sunlight, orange arrow), in W/m2, between the version with high clouds and low clouds and the version with only low clouds? Type in a positive number if it is higher in the version with both high and low clouds, or a negative number if it is higher in the version with only low clouds.

`Enter answer here`

Q4. What’s the difference, in W/m2, in outgoing longwave radiation (blue arrow), between the version with high clouds and low clouds and the version with only low clouds? Type in a positive number if it is higher in the version with both high and low clouds, or a negative number if it is higher in the version with only low clouds.

`Enter answer here`

Q5. Given the effect of the stratus cloud and the cirrus cloud on the total energy balance, which of the following would be most likely to have a warming effect on the world?

• More stratus and fewer cirrus clouds
• Fewer stratus and cirrus clouds
• More cirrus and fewer stratus clouds
• More stratus and cirrus clouds

#### Quiz 5: Model Aerosols and Climate

Q1. In this quiz, we will use the RRTM Earth’s Energy Model again. Instructions for using this model are available on the doc page by clicking on “how to”. Remember, for all numeric questions, type in your answer without the units (e.g. put “100” and not “100 K”).

Set up an atmosphere with a Lapse rate of 6 K/km, a CO2 concentration of 400 ppm, a Low Cloud (fraction) of 0.5 (50%), and a surface temperature such that the Earth loses as much energy as it gains. Once you’ve achieved these conditions, hover over the heads of the orange and blue up and down arrows to get the total incoming and outgoing shortwave and long wave (IR) radiation (four values). Keep track of these values somewhere to help answer this question.

In the drop-down aerosols menu, where it says “No aerosols” by default, select “city, just black carbon.” Don’t adjust the Earth’s surface temperature.

Now look at the four values on the orange and blue arrowheads. Calculate the difference in sunlight hitting the ground with and without black carbon, in W/m2 (remember to leave off the units). If there is less sunlight hitting the ground with black carbon, type in a negative number.

The presence of the black carbon increases how much energy is absorbed by the Earth. Notice that the mechanism by which this happens is different than with CO2.

`Enter answer here`

Q2. Now change the aerosol profile to “city, just sulfates”, which represents sulfate aerosols one might find in the boundary layer above a city. Notice that even though the sulfates reduce the amount of sunlight hitting the ground by about the same amount as the black carbon, they have a much different effect on the reflected sunlight. What’s the difference, in W/m2, between the amount of outgoing sunlight between these two situations (sulfate and black carbon)? If the sulfates reflect more, type in a positive number; if black carbon reflects more, type in a negative number.

`Enter answer here`

Q3. Based on the change in the arrows above, which of the following is true?

• The black carbon reflects more sunlight and absorbs more longwave radiation than the sulfate.
• The black carbon reflects more sunlight and the same amount of longwave radiation as the sulfate.
• The black carbon reflects more sunlight and absorbs less longwave radiation than the sulfate.
• The black carbon reflects less sunlight and absorbs the same amount of longwave radiation as the sulfate.
• The black carbon reflects less sunlight and absorbs more longwave radiation than the sulfate.
• The black carbon reflects less sunlight and absorbs less longwave radiation than the sulfate.

Q4. Water vapor molecules are a bit shy; no one water molecule wants to be the first to start a cloud droplet. However, they’re happy to latch on to other particles, such as sulfate aerosols. As a result, if there are more aerosols present, there will be more cloud droplets, though with less water each. Having smaller droplets changes the radiative properties of the cloud.

To observe this, with the above conditions (6 K/km, 400 ppm CO2, 50% low cloud fraction, “city, just sulfates” aerosol profile), adjust the temperature so that the Earth is in balance. Then, change the cloud water Drop Radius from 10 to 5 μm (1 μm = 1E-6 m = 10^-6 m). What’s the change in Earth’s overall energy balance, in W/m2? (If the Earth is now losing more energy than before, type in a negative number; otherwise, type in a positive number.)

As you enter this number, meditate on the fact that doubling CO2 reduces outgoing longwave radiation by about 4 W/m2.

`Enter answer here`

#### Quiz 6: Calculate the Climate Sensitivity

Q1. The climate sensitivity describes how much the temperature of the planet changes when you change the energy balance in some way.

One way to express the climate sensitivity is in temperature per change in energy flux (units of ˚C (or Kelvin) per change in energy flux in Watts / m2). Another more common way, called ΔT2x (delta T2x), is the amount of warming that results from a doubling of atmospheric CO2 concentration, which results in about 4 Watts / m2 of radiative forcing. ΔT2x provides a rough yardstick for climate change because atmospheric CO2 will double under business-as-usual.

First calculate the rate, in W/m2, of IR energy emission of a blackbody at 287.2 Kelvin (a value that will come up from the MODTRAN model in a couple of minutes). The value of sigma is 5.67 x 10-8 W / (m2 Kelvin4). Assume an emissivity of 1.

`Enter answer here`

Q2. Now raise the temperature by 1˚ C and calculate the change in outgoing IR, in Watts / m2.

`Enter answer here`

Q3. From question 2, you now have the change in Watts / m2 per 1˚ C. We will now rearrange this number into a ΔT2x climate sensitivity that has useful units of ˚C / (2xCO2) – the increase in temperature (˚C) per doubling of CO2 (2xCO2). Hint: Remember the radiative forcing per doubling (2xCO2) of CO2 is 4 Watts / m2 per doubling.

If you’re like me, you’ll need a pencil and paper, and you’ll need to write out what factors could combine to form the units you’re trying to build (˚C / (2xCO2)). Once you’ve figured out a formula for getting ΔT2x from two values in Watts / m2, you might find it helpful to encode/save it into a few cells in a spreadsheet, because you will be using it a few more times later in this quiz.

What value do you get for ΔT2x?

`Enter answer here`

Q4. Now bring up the MODTRAN model of IR light in the atmosphere.

Change the Locality to Subarctic Summer (which happens to have a surface temperature of 287.2 Kelvins). Change the virtual sensor Altitude (km) to 0, so that the sensor is looking directly at the ground with no air in between. What is the value of the IR energy flux, in Watts / m2?

`Enter answer here`

Q5. Enter 1 into the Ground Temperature Offset (˚C) box to raise the ground temperature 1 ˚C. (When you do this, a selector labeled holding fixed water vapor pressure will appear. Leave this alone for now; it says that the total number of water vapor molecules won’t change as we change the temperature of the atmospheric column.) The IR flux will increase as it did in your first calculation. Convert your two values for outgoing infrared energy flux (Watts / (m2 ˚C) into a doubling-CO2 climate sensitivity, ΔT2x, as you did in Question 3.

`Enter answer here`

Q6. Now raise the Altitude (km) of the virtual sensor to the default 70 km, and repeat the calculation of ΔT2x.

`Enter answer here`

Q7. The water vapor feedback to global temperature arises because the amount (pressure) of water vapor in the air increases with temperature, and water vapor is a greenhouse gas, which drives further warming. In Question 5, we held the water vapor pressure constant, so the model did not increase the amount of water vapor in the troposphere when we increased the temperature.

Now, in the Holding Fixed drop-down menu, change Water Vapor Pressure to Relative Humidity. Because the maximum concentration of water vapor (100% relative humidity) changes with temperature, the amount of water vapor will now change with temperature. Verify that this is the case by graphing Water Vapor vs. altitude on the graph on the right and looking at how the graph changes as you switch between the two settings.

What is ΔT2x when you include the water vapor feedback (Relative Humidity setting)?

`Enter answer here`

Q8. Open the Earth’s Energy model, and let’s look at it in its default configuration. What is its equilibrium temperature, in K?

`Enter answer here`

Q9. Now increase the CO2 concentration to 800 ppm. By how much do you have to increase the surface temperature (in K) to balance the Earth’s energy budget?

`Enter answer here`

Q10. Now increase the CO2 concentration further to 1200 ppm, and balance the budget again by adjusting the surface temperature. (For reference, economists project that without action to reduce fossil fuel use, the concentration will reach approximately 1000 ppm by 2100).

How much, in K, do you have to increase the temperature from its value in the 800 ppm case in order to balance the budget?

`Enter answer here`

Q11. Finally, let’s increase the CO2 concentration once more to 1600 ppm. How much do you have to increase the temperature in K from the 1200 ppm case to balance the energy budget? Notice if you see a trend in questions 9 – 11.

`Enter answer here`

Q12. Sensitivity of surface temperature to CO2 is more typically expressed in terms of a response to doubling CO2 concentration. We can get an estimate of this by comparing the change in temperature needed to balance the energy budget between the 400 ppm to 800 ppm case and the 800 to 1,600 ppm case. If you average these two temperature changes, what value do you get for the temperature response to a doubling of CO2 (in units of K)?

`Enter answer here`

#### Quiz 7: Quiz 3

Q1. Doubling the number of grid points in each spatial dimension (x, y, z) of a climate model

• makes the model run half as fast.
• makes the model run faster.
• makes the model run more than 10 times slower.

Q2. Imagine a “depression” of water (area with a relatively lower water level) on the surface of a body of water, a lake or the ocean. In which direction is pressure pushing the water in the depression?

• inward
• outward
• around the depression clockwise
• around the depression counter-clockwise

Q3. Imagine a “depression” of water (area with a relatively lower water level) on the surface of a body of water, a lake or the ocean. Water in the depression will initially flow _ before it has time to feel Earth’s rotation.

• inward
• outward
• around the depression clockwise
• around the depression counter-clockwise

Q4. Imagine a “depression” of water (area with a relatively lower water level) on the surface of a body of water, a lake or the ocean. Remember that the Coriolis acceleration in the Northern hemisphere points 90 degrees to the right of the direction of motion. Which direction will the water in the depression flow after it has had time to feel the effect of Earth’s rotation?

• outward
• inward
• around the depression counter-clockwise
• around the depression clockwise

Q5. Air pressure is lower inside a hurricane. Coriolis acceleration deflects moving fluids 90˚ to the left of the direction of flow in the Southern Hemisphere. From these facts, deduce the direction of air flow around the center of a hurricane in the Southern Hemisphere:

• clockwise
• counter-clockwise

Q6. The Coriolis effect is not experienced at the North and South Poles.

• True
• False

Q7. A positive feedback is a

• amplifier
• stabilizer

Q8. The runaway greenhouse effect, as defined in class, is a runaway of what?

• the water vapor feedback
• the carbon cycle feedback
• the ice albedo feedback

Q9. The effect of water vapor (a greenhouse gas) on Earth’s temperature is a _ feedback.

• positive
• negative

Q10. The water vapor feedback, which affects Earth’s climate, is a

• positive feedback
• negative feedback

Q11. The response of clouds to changes in Earth’s climate represents a __ feedback.

• negative
• positive

Q12. Which clouds scatter sunlight more effectively?

• low clouds
• high clouds

Q13. Which produce rain?

• high clouds
• low clouds

#### Quiz 1: Model the Global Carbon Cycle

Q1. This homework is intended to get you thinking about weathering and CO2 in the atmosphere. Answer these questions using the GEOCARB on-line geological carbon cycle model. When using the model, you may find the Save Model Run to Background button useful for comparing the results of different scenarios.

First, increase the CO2 degassing rate from the Earth, from the default value of 7.5 to 9 x 1012 moles C per year, in the Simulation column (not the Spinup column. The eventual (equilibrium) CO2 concentration in the atmosphere

• goes up
• goes down

Q2. How long does it take, in model time, for the atmospheric CO2 concentration to reach equilibrium (stop changing)? You’ll have to use your judgment to decide what “equilibrium” means here.

Q3. What is the steady-state (equilibrium) pCO2, in ppm, when the Simulation degassing rate is at 9 x 1012 mol C per year and all other parameters are at their default values?

`Enter answer here`

Q4. Now increase the Simulation degassing rate to 12 x 1012 moles C / year. What is the new steady-state CO2 concentration, in ppm?

`Enter answer here`

Q5. Do a few more runs with Simulation degassing rates spanning from 5 to 15 x 1012 moles C per year, leaving everything else at default values. Make a plot of the atmospheric steady-state CO2 concentrations you get on the x-axis, and the degassing rate on the y-axis, only label the y-axis “weathering rate”, since the rate of weathering has to be a slave to the rate of degassing. Usually in a plot you put the knob you’re turning on the x-axis and the result on the y-axis. That’s true here also, because the CO2 controls the weathering rate.

• What is the relationship between the two variables you plotted?
• concave up (curves below a line connecting 1st and last points)
• linear (a straight line)
• concave down (curves above a line connecting 1st and last points)

Q6. In this question, you will examine the effect of solar intensity on steady-state CO2 concentration. The rate of weathering is an increasing function of CO2 and sunlight, which means that an increase in CO2 will drive an increase in weathering, as will an increase in sunlight. The sun used to be less intense than it is now. Turn back the clock 500 million years (by entering 500 into the Geologic Setting box), to when the sun was cooler than today, and set both degassing rates back to 7.5 x 1012. What is the steady-state CO2 concentration, in ppm, now?

`Enter answer here`

Q7. Making the sun dimmer makes the steady-state CO2 concentration

• stay the same
• go up
• go down

Q8. Plants pump CO2 down into the soil, possibly accelerating weathering. They also stabilize soils, which perhaps decreases the weathering rate. Run a simulation with a transition from no plants to a world with plants, with no carbon spike on the transition. What happens to the rate of chemical weathering immediately after the plants are introduced? (You may have to read a bit about the model to figure out where to find the weathering rate.)

• it stays the same
• it goes up
• it goes down

Q9. What happens to the weathering rate after enough time has passed to return to equilibrium?

• it is the same as it was during the spinup phase
• it is lower than it was during the spinup phase
• it is higher than it was during the spinup phase

Q10. The CO2 concentration __ immediately after plants were added.

• increased
• stayed the same
• decreased

Q11. When the atmospheric CO2 concentration changes in this model, where does the extra carbon go?

• into soil carbon
• into CaCO3
• into plants

#### Quiz 2: Model Ocean/Land CO₂ Uptake with ISAM

Q1. Bring up the ISAM integrated climate model. Run the model with a High Business as Usual Scenario. Change the plot on the lower right to show Cumulative Carbon Fluxes. Positive numbers mean carbon released to the atmosphere.

Mouse over the plot to determine the amount of carbon, in Gton, that went into the ocean by the end of the simulation in the year 2100.

`Enter answer here`

Q2. What fraction of the cumulative fossil fuel carbon ended up in the ocean?

Q3. Do another run using a Rampdown 80% by 2050 scenario and repeat the calculation. What fraction of the fossil fuel carbon is in the ocean by 2100?

Q4. The Net Land Use flux is from deforestation. The Net Land flux is carbon uptake on land in places that were not deforested plus Net Land Use. In the High Business as Usual scenario, is the land surface a net source or sink of carbon by 2100?

• source
• sink
• not much of either, because the deforestation and stimulated uptake are about the same

Q5. Switch back to the Rampdown scenario. Is the land surface a net source or sink of carbon in this scenario?

• source
• sink
• not much of either, because the deforestation and stimulated uptake are about the same

Q6. From this we can conclude that, in the ISAM model, climate change and rising atmospheric CO2 concentrations cause the undeforested landscape to

• take up carbon
• do nothing much
• give off carbon

#### Quiz 3: Model Intended vs. Greenhouse Yields

Q1. This exercise makes use of the Slugulator on-line greenhouse gas model.

Set the CO2 spike size to zero, and leave the CH4 spike size at 1 Gton C. Look on the table on the right to find the energy yields from burning coal to make CO2 (but we’re not making any slugs of CO2 today, so that value should read “0”), and the energy we would have gotten from burning the CH4 instead of emitting it. The units of that number are Joules. Given a human appetite for energy at the rate of 1013 Watts, how long could this Gton have kept us going, if we used it 100% efficiently, in years? You may have to do a bit of algebra to answer this question.

`Enter answer here`

Q2. Set the time horizon selector to Show 10 years. The Time Integrated Radiative Forcing for CH4 is given in the middle of the table. What is the ratio of the radiative forcing from that methane to its Energy Yield as a fossil fuel?

• less than 1
• between 10-20
• between 500-600
• between 100-200
• between 1000-1200

Q3. Now zoom out in time. As you expand the time horizon, the amount of warming (time-integrated) from the CO2, which the CH4 turned into, starts to become significant. About how many years does it take for the total warming (time-integrated) from the CO2 to exceed that from the CH4?

• a bit under 50 years
• a bit under 100 years
• a bit under 500 years
• a bit under 1000 years

#### Quiz 4: Quiz 4

Q1. If you accelerate the rate of weathering by building mountains (exposing more rock to the atmosphere), Earth’s climate will

• cool
• warm

Q2. At high temperature, the equilibrium state of the Urey reaction favors carbon in the form of _.

• CaCO3
• CO2

Q3. CO2 uptake by weathering rocks acting on temperature is a __ feedback

• positive
• negative

Q4. On long time scales, fluctuations in atmospheric CO2 driven by exchange with _ are governed by a positive feedback response to Earth’s climate

• the oceans
• the solid earth
• the land surface

Q5. Which of these holds the smallest amount of carbon?

• ocean
• land surface
• solid Earth

Q6. Which of the following reservoirs contains the most carbon?

• living things
• the ocean
• the land surface
• the atmosphere

Q7. Which of the following molecules contains the most reduced form of carbon?

• CO2
• CH2O
• CH4

Q8. Which of the following consists of long, linear chains of carbon atoms?

• natural gas
• oil
• coal

Q9. Which of the following is mainly used to generate electricity?

• oil
• coal
• gas

Q10. Which of the following is most useful as a fuel for transportation?

• oil
• natural gas
• coal

Q11. Our use of which of the following will mainly determine whether the earth cooks or not?

• natural gas
• oil
• coal

#### Quiz 1: Model Hubbert’s Peak

Q1. Answer these questions using the Hubbert’s Peak plotter. You will see two different data sets to plot against, along with the three parameters (knobs) that control the shape of the Hubbert curve. Nothing fancy here, we’re just eyeballing the fit of the curve to the data.

Start by looking at US Oil Production. When you first load the model, you’ll see a curve that fits the data pretty well, but see if you can make it fit even better by varying the parameters (Peak Year, Peak Width, and Total Reservoir Size) in the boxes on the left. You might have to change some parameters together to improve the fit. What do you think is the best guess for the Peak Year of U.S. oil production?

`Enter answer here`

Q2. Now look at World Oil Production. Set the initial global inventory of oil (Total Reservoir Size) to 250 Gton C, and tune the values of the Peak Year and Peak Width to find a good fit to the data. When do you think the peak of oil extraction will be?

`Enter answer here`

Q3. Now increase the Total Reservoir Size (the total amount of petroleum we were blessed with) to 500 Gton C and tune the other parameters to find a good fit to the data. What value of the Peak Year fits best?

`Enter answer here`

Q4. Now check out the production rate of whale oil. In order to fit the data, how much whale oil, in Gton, do you need (in the Total Reservoir Size box)?

(Hint: There are not very many gigatons of whale oil harvested per year. Decrease the reservoir size by factors of 10 until you see the data in a reasonable range.)

`Enter answer here`

#### Quiz 2: Model Kaya Identity

Q1. Start up the Kaya Identity model. The model can be used to forecast the rate of growth of CO2 emissions as it is driven by factors of population, GDP, energy intensity, and carbon efficiency.

First we’ll tune the rate of change of \$GDP / (yr person) so that it grows or declines in the future the same as it has been doing in the past. Not that this is necessarily the way the future will go, but it provides a first guess at a business-as-usual scenario where nothing is done to avoid climate change. You can see past values and the model fit by selecting GDP per Capita on the pulldown menu over one of the plots, or if you hover your mouse over the input box below the term in the formula, the plot will switch to show you that. A positive value indicates growth, i.e., a value of 1 means growing at 1 percent per year. What value of the growth rate do you think best fits the past data? Give your answer in % per year, but remember not to type the % sign in your answer.

Hint: When fitting the data, make sure it isn’t flat along the x-axis so you can actually evaluate how good the fit is. You’ll have to use your judgment.

`Enter answer here`

Q2. Now adjust the growth / decline rate of the next term, Watt yr / \$, the energy intensity. What value, in % per year, fits the data best?

`Enter answer here`

Q3. The third term, the Carbon Intensity, is expressed as Carbon released (in gigatons) per Energy produced (in teraWatt-years). Look at the plot for this term; the value has been dropping through time. This means that people have been getting

• less carbon efficient
• more carbon efficient.

Q4. What value, in % per year, of the rate of change of Carbon Intensity best fits the historical trend in the data?

`Enter answer here`

Q5. Let’s build a worst-case scenario. Set Population to 13 billion, and set the \$GDP/(yr person) growth rate to 2%. We need to find the worst-case value of the growth/decay rate of the Energy Intensity that matches at least some of the historical data fairly well. In which direction would you tune the energy intensity to get higher carbon emissions?

a lesser number (more negative)

a greater number (less negative)

Q6. What is the worst-case value, in %, of the Energy Intensity decay rate that still makes the curve go through at least some of the historical data?

`Enter answer here`

Q7. What is the worst-case value, in %, of the Carbon Intensity decay rate that still makes the curve go through at least some of the historical data?

`Enter answer here`

Q8. What is the forecasted rate of carbon emissions in the year 2100 in this worst case scenario, in Gton C / yr?

`Enter answer here`

Q9.Now let’s find a stabilization pathway. Set the eventual Population level to 11 billion, and the \$GDP/(yr person) growth rate to 1.6%. Assume that the Energy Intensity declines at the same rate as in Question 6. What is the maximum rate of change in Carbon Intensity required to keep the atmospheric CO2 from rising above a value of 450 ppm? (We are looking for a negative number, in percent, as close to zero as possible.)

`Enter answer here`

Q10. A target of 80% cuts in emissions by the year 2050 has been floated as a goal that would enable us to avoid the worst of climate change. You can see that scenario, for example, in the ISAM model. One formula for an exponential decline is:

C(t) = C(0) x e-k t

where C is the rate of carbon emissions, C(0) is the initial rate, C(t) is the rate at time t, k is approximately the rate of decline (NOT in %), and e is the exponential constant (≈ 2.718). Assuming we start in 2015 and reduce emissions by 80% by 2050 (in 35 years), what annual rate of emissions cuts would be required, in percent?

`Enter answer here`

#### Quiz 3: Model Methane and Slugulator

Q1. Bring up the Methane in the Atmosphere model. First look at the Like Today part of the simulation, in which the methane budget and concentration relax to an equilibrium with a chronic anthropogenic (human-caused) source in addition to the natural sources. The default case (as the model comes up) has the anthropogenic methane flux not quite equal to the natural, so that there has been just a bit less than one doubling in the emission flux.

Change to the Methane Concentration plot and calculate the ratio of the equilibrium methane concentration in the human-impacted (Like Today) part to the equilibrium concentration in the Natural part. The ratio for atmospheric CO2, for reference, is about 1.42 (42% increase). For methane, the ratio is

• a bit more than 2
• exactly 2
• a bit less than 2

Q2. Change to the CH4 Lifetime plot to see the average amount of time that a methane molecule can expect to live before it gets oxidized, plotted as a function of time. This plot shows why the change in the methane concentration is not exactly proportional to the change in emission flux. The lifetime of methane in the atmosphere _ when the emission flux increases.

• decreases
• increases
• stays the same

Q3. Now look at the Slug Time! part of the plot. There is a lot of carbon frozen in permafrost and methane hydrates, both on land and beneath oceanic continental shelves, in the Arctic – enough that 5% of it would be about 50 Gton C, a significant slug. This methane will probably be released on a time scale of about 100 years, because it takes a long time for enough heat to conduct downward into the ground to melt permafrost. The time scale of how quickly it can come out is crucial, as you will see in this exercise.

Keep the Slug size at 50 Gton C, and vary the emission timescale of this release. The maximum CH4 concentration you can reach (at any time) by varying the emission timescale is __ than the steady-state (equilibrium) anthropogenic concentration.

Q4. Now set the emission timescale to 100 years. Switch to the Radiative Forcing plot to compare the Watts/m2 impact of the 50 Gton C slug with that of business-as-usual fossil fuel CO2. The maximum RF from the methane from the year 0 to the year 100 is _ the maximum impact from the CO2 during this same period.

• twice as large as

Q5. Now switch the duration of the slug to only one year, to simulate a spike release of methane. How does the maximum radiative forcing of the methane compare to the maximum radiative forcing from business-as-usual CO2, on the time frame of now to the year 2100?

• they are about the same
• methane is twice as strong
• methane forcing is about half that of CO2

Q6. Now bring up the Slugulator model, which compares the radiative forcings and also the climate impacts of releasing individual slugs of greenhouse gases CO2 or methane. When methane is released, it oxidizes to CO2 within about 10 years. So we can compare the two gases on an equal footing by releasing just CH4 and not any CO2. Set the CO2 spike size to 0 and leave the CH4 spike size at 1 Gton C. Change to the Radiative Forcing plot and use the mouse hover to see the values, or just estimate them from the y-axis on the plot. What is the ratio between the maximum RF from CH4 to that of CO2?

Q7. Change to the Deep Ocean Temperature Anomaly plot. There are two curves: one is excess heat from methane as a greenhouse gas (red) and the other is heat from CO2 (blue). Over what time scale does the ocean absorb heat because of the methane? In other words, in what year does the temperature contribution from CH4 peak?

Q8. Over what time scale does the ocean absorb heat because of the CO2?

Q9. How long does it take before the deep ocean temperature impact from the CO2 exceeds that from the CH4?

#### Quiz 1: Make Maps of Climate Models Warming

Q1. You’ll need the AR5 Climate Model Mapper for this exercise.

Annual mean temperature anomalies in 2100. For each of at least 3 models, get the year 2000 map of Surface Temperature, and also the year 2099 map (some of the models don’t go all the way to 2100). Click the Calculate Anomalies button to subtract the year 2000 temperatures from the year 2099 temperatures (to calculate the temperature anomaly). The anomaly calculations are only done within a given model, so that they are on the same grid. Note that the anomaly plots for the year 2000 will all look the same, because they have all been converted to zero (change from the year 2000). Mouse over the year 2099 entries in the list of maps to see them. The temperature changes you see in the Arctic are ________.

• closest to 1 ˚C
• closest to 3 ˚C
• closest to 10 ˚C

Q2. The temperature changes you see in most other parts of the world, the more “normal” values, are

• closest to 1 ˚C
• closest to 3 ˚C
• closest to 10 ˚C

#### Quiz 2: Look for the Smoking Gun

Q1. Bring up the GHCNM Met Station and AR5 Model Browser. The goal of this exercise is to estimate the global average temperature change by putting together a bunch of data from meteorological stations, and compare those results with climate model output.

First go through and select at least 10 stations. You want global coverage, so pay attention to where the selected stations are on the map as you build your list. It might be useful to select Latitude as the bin type, then go through the latitude bands one at a time to ensure global coverage. Also choose the stations according to the length of time over which they have data. You want stations with data that begins at around 1900 and, for the most part, spans to about the present day.

After you have selected your stations, copy and paste the entire URL for the Time Series Browser into the space below.

`Enter answer here`

Q2. When you have the stations, Normalize them (subtract out the average temperature values from 1900-1950, using the Norm 1900-50 button), then combine them into a single Composite record. Calculate the Temperature Trend for the Time Range from 1970 to 2013. (You’ll have to click on Averages.) What value of the temperature trend, in ˚C/decade, do you get for your composite station?

`Enter answer here`

Q3. Now go to the AR5 Models page and select one of the global climate models there. Select the Human + Natural So Far scenario and wait for it to finish downloading. Then select the Natural Only So Far scenario and wait for it to finish downloading. Which of the two scenarios do you think is a better approximation to the data?

NOTE: Due to limitations in the platform, this question is not graded properly (it doesn’t actually check your results), so I’ll just for now tell to you:

• Choose this answer to get the point

Q4. Now start with a fresh copy of the webpage by clicking here.

Compile another list of stations that are close to water by selecting the WATER vegetation type bin. This will narrow the stations in the list and on the map. This will take a bit more picking, but find 10 stations that have at least a few years of data before 1950 (so it can be normalized) and span to near the present-day. What is the URL of the browser when you have the list done?

`Enter answer here`

Q5. Normalize and Combine the stations as you did before. What value to you find for the temperature trend, in ˚C/decade, for the Time Range from 1970 to 2013?

`Enter answer here`

#### Quiz 3: Model Borehole Temperatures

Q1. Bring up the on-line model for temperature and other stuff in a soil column, at http://climatemodels.uchicago.edu/permafrost/ . In the default model run, you will see ice and methane hydrate, but we want to eliminate that for these experiments, so start out by changing the Initial Surface Temperature to 0. The ice and hydrate will disappear in the equilibrium simulation for this condition. The temperature profile will be a straight line with depth, getting warmer because of the geothermal heat flow coming in from below.

Now trigger a transient run by changing the New Surface Temperature to 6 degrees (a seriously polar-amplified global warming scenario). The model will evolve forward through time. You can see the temperatures at the top and the bottom of the soil column, in the Temperature plot in the lower right.

How long does it take for the temperature at the bottom of the soil column (800 meters depth in the default simulation) to reach a new steady value?

• more than 10000 years

Q2. Now zoom in, in time, by changing the Model Time Span parameter to 1000 years. The model will run a transient in time again, but it will take shorter steps in time, so that we can see better what happens right at the beginning. When the run is finished, use the slider bar on the right to slide the plots back toward the beginning of the simulation. As you slide back in time, watch the profile of temperature with depth in the upper left plot.

At some points in the simulation, the temperature profile is not straight but slightly curved. This curvature is an important part of how borehole temperature profiles are “inverted” to estimate the amount of temperature change, and how long ago it occurred.

At what point in the simulation is the temperature profile the most curved?

• in the steady initial condition (time 0)
• just after the transient run begins (time just after 0)

#### Quiz 4: Analyze Recent Solar Intensity Changes

Q1. Open the Climate Time Series Browser

Under Forcings, find the Solar Intensity on the list and select it to see the plot of the radiative forcing from variations in the intensity of the sun. You will see a regular cycle in the solar intensity. The period of this cycle is about

• 3-4 years
• 10 years
• 50 years
• one year

Q2. There is also a kind of general increase in the sun’s luminosity as you go from the late 1800’s to the 1950’s. What is the change in radiative forcing, in W/m2, that this change causes?

`Enter answer here`

Q3. A middle-of-the-road value for the Climate Sensitivity expressed in energy terms is 0.75˚ C / (Watts/m2). This corresponds to the more memorable ΔT2x (delta T2x) the temperature change from doubling CO2, of 3 ˚C.

Using this value of the Climate Sensitivity, convert the change in solar RF into an equilibrium temperature change in ˚C.

`Enter answer here`

Q4. Averaging over the solar cycles, what is the change in solar intensity radiative forcing between the 1950’s and today, in Watts / m2?

`Enter answer here`

#### Quiz 5: Quiz 6

Q1. The smoking gun for a human impact on the climate of the Earth is

• the thermometer temperature record
• the Medieval climate
• the hockey stick
• the ozone hole

Q2. About how long did the Little Ice Age last?

• a few years
• >1000 years
• a few centuries
• tens of years
• 1000 years

Q3. About how much warmer is the Earth now than it would be naturally?

• 0.1 ° C
• 3 ° C
• 1 ° C
• 5 ° C

Q4. The Last Glacial Maximum was caused by

• a change in the intrinsic intensity of the sun
• the butterfly effect
• a change in the Earth’s orbit around the sun

Q5. Ice core records show that global temperature can have an impact on atmospheric CO2.

• false
• true

Q6. The bucket effect in sea surface temperatue measurement is

• an old sea story
• comparable to global warming when calculating the global average
• a real effect but not significant when calculating the global average

#### Quiz 1: Water Stress in Climate Model Results

Q1. Load the AR5 Climate Model Mapper page.

Make maps of Soil Moisture from the CCSM4 and CanESM2 models, years 2000 and 2099, with the default Plot Settings, and then Calculate Anomalies (you may want to read the model instructions to learn what Calculate Anomalies does).

Red colors indicate wetter soils, blue colors indicate drier soils. Select all the regions from the list below which are drier in 2099 than in 2000 for both models.

• Southern Africa
• Western Australia
• The Amazon (eastern Brazil)
• Eastern Australia
• The Mediterranean
• Northern Europe

Q2. For at least three different models, calculate anomalies in Precipitation between 2000 and 2099. Most of the change in precipitation patterns is found

• in continental interiors
• in a band along the equator
• in the high latitudes

Q3. Get rid of any previous maps you have loaded by reloading the page, or clicking on the entries for the old maps in the list. Make a beautiful movie of the seasonal cycle of monthly precipitation rates. Select Precipitation, a model, and a year.

Under Plot Settings, change Annual Mean to January. Then change it again for all 12 months. Press the Slide Show button, which then changes to a Show Movie button. Play the movie. Sit and gaze at the movie for a few minutes.

• Nothing!
• it’s alive!

#### Quiz 2: Model Permafrost

Q1. Bring up the Permafrost simulator at http://climatemodels.uchicago.edu/permafrost/ . The default simulation is cold enough at the surface that there is a zone at depth where methane hydrate is stable, a form of water ice that contains molecules of the gas methane. We’re thinking about permafrost for now, so increase the Initial Surface Temperature to -6 degrees, which will eliminate the hydrate deposits. Now trigger a transient run by changing the New Surface Temperature to -4 (a moderate 2 degree warming). As the simulation evolves through time, the amount of ice is plotted as the blue line in the Inventory plot in the lower right.

How many years does it take for the inventory of ice to reach a new steady value?

• more than 10 000 years

Q2. Change the Initial Surface Temperature to -3 degrees, and the New Surface Temperature to -1 degrees, to simulate the same warming at the edge of the permafrost zone, where the average temperature is closer to freezing. How does the timing of this response compare with the results you got, deeper in the permafrost zone?

• the time scale is about the same
• it’s faster near the edge of the permafrost zone
• it’s faster deeper in the permafrost zone

Q3. Now reload the model to reset everything to default conditions. You will see a permafrost zone, and below that, a methane hydrate zone appears. Set the New Surface Temperature to -6 degrees, to trigger a run with the same warming as the experiments you did before. Watch the Inventory plot for changes in the inventory of methane hydrate at that location.

As you may remember from our discussion of methane as a greenhouse gas in the atmosphere, to get a spike of methane concentration, you need to release a bunch of methane in a time span which is short compared to the methane lifetime in the atmosphere, which is about 10 years.

How does the methane hydrate decomposition time scale compare with the methane atmospheric lifetime?

• hydrate methane is released quickly compared to the atmospheric lifetime (so we’d get a concentration spike in the atmosphere)
• hydrate decomposition is slow compared to atmospheric degradation (so the concentration would rise a bit but no spike)

#### Quiz 3: Model Changes in Sea Level

Q1. Bring up the ISAM integrated climate model.

Run the model for a High Business-as-Usual Scenario. By how much does the model sea level change by the year 2100, in cm, relative to the sea level at the beginning of the plot (in the year 1765)?

`Enter answer here`

Q2. Based on the sea level plot, showing different contributions from different sources, which of the following are the two largest contributors to this sea level change? (Choose 2)

• Greenland
• ThermExp (thermal expansion of seawater)
• Glaciers
• Antarctica

Q3. Change to the Rampdown 80% by 2050 scenario. By how much does the model sea level change by the year 2100, in cm, relative to the sea level at the beginning of the plot (in the year 1765)?

`Enter answer here`

Q4. The Atmospheric CO2 concentration in this rampdown scenario is _ in the year 2100.

• rising
• falling

Q5. Sea level is _ in the year 2100 in the rampdown scenario.

• falling
• rising

#### Quiz 4: Play with an Ice Sheet Model, ISM

Q1. Bring up the ISM model.

Which ice sheet is more sensitive to an increase in temperature, Greenland or Antarctica?

Compare the two ice sheets by slugging them with CO2 and/or by increasing the temperature

(vertical slider). The Save button doesn’t apply between settings, so you’ll have to play with each ice sheet separately. Try to make your CO2 slugs and temperature settings about the same for each of the ice sheets to compare them with roughly equal forcing.

• Greenland
• Antarctica

Q2. Switch to the Greenland setting, and do a model run in which the ice sheet melts down. (Make it melt as slowly as you can). You can clobber it with several 1000 Gton C pulses in a row (boxes in the upper right) until it collapses, or drive it to ruin using the temperature slider (far left by the axis of the temperature plot). Stop the simulation and click Save. This is your “control” run. Engage the optional model settings (in the check boxes on the upper left) one at a time, to do comparative runs.

The Sea level change setting drives sea level to rise in proportion to changes in the global temperature. This is not due to the effect of your particular ice sheet on sea level, but rather it assumes that all of the ice sheets on Earth are melting as the temperature rises, the same way they did as the last Glacial maximum ended. Note that the proportionality between sea level and global temperature derived from the paleo record gives a whole lot more sea level rise than the IPCC forecasts for the year 2100 because this model runs on a long enough time scale for the ice sheets to respond.

Turning on the Sea level change option causes the ice sheet to

• collapse before the “control” run even gets started
• persist until the “control” run is long gone
• (no impact)
• pretty much follow the “control” run but collapse a bit faster at the end
• persist just a bit longer than the “control” run before collapsing right at the end

Q3. Using the same Control simulation in which the ice sheet melts down, do a Live model run with Isostatic bed adjustment. What happens to the bedrock under the ice sheet after the ice sheet melts?

• it rises while the control stays the same
• it stays the same while the control run falls
• it falls while the control stays the same

Q4. Now compare the ice elevation between your Isostatic bed adjustment run with your Control run from Question 2. The process of isostatic bed adjustment causes the ice sheet to

• collapse before the “control” run starts to collapse
• pretty much follow the “control” run but collapse a bit faster at the end
• (no impact)
• persist just a bit longer than the “control” run before collapsing right at the end
• persist until the “control” run is long gone

Q5. Now turn off Isostatic bed adjustment, and turn on Ice-temperature coupling, which allows changes in ice temperature to affect the viscosity of the ice. Keep the same Control run as you have had all along. This process causes the ice sheet to

• pretty much follow the “control” run but collapse a bit faster at the end
• (no impact)
• persist until the “control” run is long gone
• collapse before the “control” run even starts to collapse
• persist just a bit longer than the “control” run before collapsing right at the end

Q6. Now turn off Ice-temperature coupling, and turn on Basal sliding. Compared to the Control run, Basal Sliding causes the ice sheet to

• collapse before the “control” run even starts to collapse
• pretty much follow the “control” run but a bit faster at the end
• (no impact)
• persist just a bit longer than the “control” run, right at the end
• persist until the “control” run is long gone

#### Quiz 5: Short vs Long Term Sea Level Change

Q1. Bring up the ISAM integrated climate system model.

For the High Business-as-Usual scenario, what is the total amount of CO2 released because of human activity by the year 2100, in Gton C? You can find this in the Cum. Carbon Fluxes plot. Use the sum of Cum. Fossil and Cum. Land Use.

`Enter answer here`

Q2. What is the maximum temperature the model reaches by the year 2100 in the High Business-as-Usual scenario? Give your answer in ˚C relative to 1970.

`Enter answer here`

Q3. Here is a reconstruction of changes in sea level from the geologic past, modified from Global Warming, Understanding the Forecast. The x-axis is the global average temperature (we are at about 15 ˚C today). The vertical axis is sea level relative to today.

To plot the output from the ISAM model on that plot, you would have to add the present-day global average temperature of 15 ˚C to the temperatures ISAM gives you (which are temperature anomalies relative to 1970). Note also that ISAM gives sea level changes in cm, not m. The High Business-as-Usual scenario in the year 2100 shows

• less sea level change than paleo records
• more sea level change than paleo records

Q4. What is the slope of the line in the graph shown in Question 3, in m/˚C? That is, find the change in sea level per change in temperature.

`Enter answer here`

Q5. Now multiply your maximum warming from the Question 2 by the Δ(Sea level) /ΔT relationship from the geologic past to get the expected eventual geological-timescale change in sea level from anthropogenic CO2. In using this formula, we are assuming that

the maximum temperature from the ISAM is a reasonable approximation for the long-term plateau temperature, which will

last long enough, due to the long tail of the CO2, for ice sheets to respond

the ice sheets will eventually respond in the future the way they did in the past (a shot in the dark but maybe a reasonable place to start)

What value do you get for the potential geologically-eventual change in sea level, in meters due to business-as-usual CO2 emissions to the year 2100?

`Enter answer here`

Q6. How does the geologically-eventual sea level change compare to the change in the year 2100?

• geologically-eventual change is a factor of 10 smaller
• geologically-eventual change is a factor of two larger
• geologically-eventual change is a factor of 100 smaller
• geologically-eventual change is a factor of 100 larger
• geologically-eventual change is a factor of 10 larger

#### Quiz 7: Find the Increase in Low-Level Humidity in Models

Q1. Bring up the AR5 Model Mapper page.

From at least three models, make maps of the Specific Humidity at an atmospheric pressure of 90,000 Pa (an input box which pops up when you select Specific Humidity). Make maps of the years 2000 and 2099. You might need to fix the color scales using the Zoom color scale button.

In general (among the different years and models), the highest water vapor concentrations are found where?

• low latitudes
• there is no systematic difference between low and high latitudes
• high latitudes

Q2. In these regions, between the years 2000 and 2099, the water vapor (humidity) increases by about how much?

• 200%
• 1%
• 20%
• 100%

#### Quiz 8: Extract AR5 Model Lapse Rates

Q1. Open the AR5 Climate Model Mapper page.

Choose a model and bring up maps of Surface Temperature for the years 2000 and 2099. Note that when you change the year you don’t need to click on the Download map button; since the year box is on the Actions side, it gets the download going for you.

Next bring up Atmospheric Temperature, which is a 3-dimensional grid of numbers, the third dimension being pressure in Pascals (Pa). Use the default 50,000 Pa, which is about halfway up the atmosphere, pressure-wise, and is in the middle of the troposphere. Bring up years 2000 and 2099.

Calculate Anomalies and wait a moment for the maps to redraw. You can see the anomaly plots by mousing over the names of your downloaded maps on the lower left. Look at a region of the Earth where you think hurricanes are likely to form.

What is the change in surface temperature between 2000 and 2099, in ˚C, in that region for the model you selected?

`Enter answer here`

Q2. What is the change in the high-altitude (50,000 Pa) temperature between 2000 and 2099, in ˚C, in the model you selected?

`Enter answer here`

Q3. In terms of the future intensity of hurricanes, the temperature changes at low and high altitude

• work together to make hurricanes stronger
• work against each other
• work together to make hurricanes weaker

#### Quiz 9: Model Hurricanes

Q1. Bring up the hurricane simulator at http://climatemodels.uchicago.edu/hurricane/ . A hurricane is driven by energy which is absorbed by water as it evaporates, and released when it condenses again. The model on that page comes up with a default simulation, which plays as an animation. What is the wind speed of the hurricane after it forms, in meters / second?

• more than 70

Q2. Do automobiles typically go as fast as 70 m/s?

• yes, all the time
• no, only on the autobahn

Q3. In the default model run the effects of ocean mixing are disabled. Mixing in the ocean tends to make the sea surface colder, by mixing cold water up from below. The model is “idealized”, meaning that ocean mixing is either turned off, in which case the driving sea surface temperature remains constant, or on, in which case it cools down. In reality, a hurricane moves over the ocean surface, so sometimes it sees warm water unaffected by mixing, and other times it sits over a cold spot over its own making. Here is a NASA animation of satellite images of Hurricane Katrina (http://svs.gsfc.nasa.gov/vis/a000000/a003200/a003222/).

Turn on ocean mixing by clicking the checkbox, get a new model run. What is the average wind speed of this new simulation, in m/s?

• over 70

Q4. Change the plot in the lower right to Ocean Surface Temperature Anomaly by selecting it in the pull-down menu over it. The animation will re-play, and you can watch the change in temperature (a negative anomaly means the hurricane made the ocean surface colder). How much colder does the ocean surface get, in centigrade?

Q5. If you raise the temperature of the ocean surface by 3 degrees C, what happens to the sustained wind speed of the hurricane

• it goes down by 50%
• It gets about 10% smaller
• It stays about the same.
• It gets about 10% larger
• It gets 50% larger

Q6. How long does a hurricane last over land? Start from the default simulation (maybe reload the page). Check the box labeled Make Landfall and, in the Landfall on Day box that appears, set the day to 15, so that the storm is fully developed when it hits land. Click Get New Run and watch how the wind speed drops after day 15.

For a process that decays toward a new equilibrium like this, a decay time is often defined as the amount of time it takes to reach a value where the fraction of change remaining is 1/e, where e is the exponential constant, 2.787…. A value for the fraction 1/e is about 36%.

How long does it take for the wind speeds to decay to 36% of the storm value?

#### Quiz 10: Quiz 7

Q1. The strongest impacts of global warming are likely to be

• more rainfall
• it depends on where you are
• the higher average temperature (~3 ˚C)
• drying

Q2. Which two of these climate impacts exacerbate each other?

• hurricanes
• ocean acidification
• sea level rise
• droughts

Q3. Seawater is bad for crops because it is

• salty
• cold

Q4. There is a recognized possibility of a runaway ice melting feedback in the _ Antarctic ice sheet

• West
• East

Q5. A comparison of ice sheet model results and reconstructions of prehistoric changes in sea level suggests that the models might be too __ .

• sluggish
• sensitive

Q6. Where in a hurricane does a phase change for water absorb heat?

• at the sea surface where it evaporates
• in the air column where it condenses

Q7. The number of hurricanes per year is well known to increase with increasing temperature.

• false
• true

Q8. The climate change effect that most directly affects trees in the Rocky Mountains is

• higher temperatures
• lack of water
• bugs

Q9. The melting of which of the following raise(s) sea level? (Choose all that apply)

• sea ice
• ice shelves
• mountain glaciers
• ice sheets

Q10. The global rate of rainfall is expected to _ in a warming world.

• stay the same
• increase
• decrease

#### Quiz 1: Model Stabilization Scenarios

Q1. Open the ISAM integrated climate system model.

Which of the following scenarios qualify as stabilizing the atmospheric CO2 concentration below 450 ppm?

• Rampdown 80% by 2050

#### Quiz 2: Model Temperature Targets

Q1. Back to the ISAM integrated climate model.

In which of the following scenarios does it seem likely that the change in Earth’s temperature will stabilize at a value below 2 ˚C?

• Rampdown 80% by 2050

#### Quiz 3: How well does Slugulator do at Slug Theory?

Q1. Bring up the Slugulator model. Zero out the methane slug, set the CO2 slug size to 1000 Gton C, and leave everything else at their default values. What is the peak warming (maximum Surface T. Anomaly) you get, in ˚C?

`Enter answer here`

Q2. Based on the material presented in the lecture, what peak warming were you looking for?

• 1 ˚C
• 2 ˚C
• 3 ˚C
• 4 ˚C

Q3. One difference between the carbon cycle models that were aggregated into the Slug Theory as described in lecture is that they have land biosphere carbon reservoirs which take up carbon, while Slugulator does not. Give Slugulator the benefit of that land carbon uptake by decreasing the slug size until you get a peak of about 2 ˚C of peak warming. About how much carbon does it take to reach 2 ˚C?

• 800 Gton C
• 400 Gton C
• 1000 Gton C
• 200 Gton C
• 600 Gton C

Q4. You may want to start a spreadsheet to store and plot some numbers for this question, or get a piece of paper and pencil. Find the peak temperature for slug sizes of 300, 600, 900, 1200, and 2400 Gton C. Plot the temperature anomalies on the y-axis against the slug sizes on the x-axis. The curve in your plot is

• concave up (lies below a straight line connecting the first and last points)
• concave down (lies above a straight line connecting the first and last points)

Q5. If you limit the slug to half of our “base case” of 600 Gton, (that is, if we slug the model with only 300 Gton C), what peak warming do you get, in ˚C?

`Enter answer here`

Q6. The peak warming from 300 Gton C is __ half the peak warming from 600 Gton C.

• less than
• greater than
• equal to

#### Quiz 4: Model CO2 Sequestration

Q1. Bring up the ISAM integrated climate model.

Imagine that we become carbon neutral, perhaps by using carbon capture to offset all of our carbon emissions. Look at the High Business-as-usual scenario, and begin by setting the CO2 emission flux from Fossil Fuels to 0 in the year 2100. The knobs for CO2 flux in the ISAM model are rather coarse; this change results in a linear rampdown from the previous time point, the year 2075, as shown in the Model Inputs plot.

Does this scenario keep the temperature change below 2 ˚C? If not, continue backward in time and set the previous CO2 emission flux (in 2075) to 0, and so on, until you find a “stabilized” outcome where the global temperature anomaly reaches a maximum at about 2 ˚C or less. By what year do we need to become carbon-neutral in this scenario?

• 2075
• 2025
• 2050
• 2100

#### Quiz 5: Model SRM Geoengineering

Q1. Bring up the RRTM atmospheric column radiation model.

In the aerosols drop-down menu (which initially says “No aerosols”), choose the “City, just sulfates” option.

Doubling atmospheric CO2 results in a radiative forcing of about 4 Watts / m2. How does the radiative forcing from sulfate aerosols compare with that of doubled CO2?

• The sulfate aerosols are about as powerful (on the same order of magnitude) as doubled CO2
• The sulfate aerosols are about ten times as powerful as doubled CO2
• The sulfate aerosols are about one tenth as powerful as doubled CO2
• The sulfate aerosols are about twice as powerful as doubled CO2

Q2. For Solar Radiation Management to negate the entire temperature impact of releasing CO2, it would have to continue for __. (You might have to refer to past lectures to answer this question).

#### Quiz 6: How Many Wedges?

Q1. Bring up the ISAM integrated climate model.

First choose a scenario from the drop-down menu that will stabilize atmospheric CO2 concentrations, so that it looks like the global temperature won’t rise more than 2 ˚C (even after the year 2100), and Save This Model Run to Background. Next, compare the fossil Carbon Flux in the year 2050 between this stabilization scenario and the High Business-as-usual scenario. How many wedges, at 1 Gton C / year per wedge, does it take to get from the High business-as-usual scenario to the stabilization scenario?

`Enter answer here`

#### Quiz 7: How Much Carbon-Free Energy by 2100?

Q1. Bring up the Kaya Identity calculator.

Leave the population plateau at 9 billion. Tune the growth / decline rates of the other three parameters (GDP per capita, Energy intensity, and Carbon intensity) so that your graphs match the historical data for each parameter pretty closely. After you’ve done this, change one of the plots to look at Carbon-free energy needed. This is a calculation of the difference between the CO2 emissions that Kaya wants, minus the CO2 fluxes that ISAM wants in order to stabilize atmospheric CO2 at various levels, denoted by colors in the plot.

Let’s say that an atmospheric CO2 concentration of 450 ppm is a good stabilization target. (If you don’t believe me, go back to the ISAM model and choose the Rampdown scenario.) Today we produce about 13 TeraWatts (TW) of energy. How much carbon-free energy is needed in the year 2100 to stabilize the climate at this target?

• Within an order of magnitude of what we produce today (total)
• Ten times less than the total amount of energy than we produce today
• Ten times more than we produce today (total)

#### Quiz 8: Quiz

Q1. Twice the preanthropogenic atmospheric CO2 concentration is about

• 650 ppm
• 450 ppm
• 550 ppm
• 750 ppm

Q2. Further global warming of _ would stay within the range experienced by civilized humanity.

• 1 ˚C
• 2 ˚C
• 3 ˚C
• none of these

Q3. We’ve already emitted __ of the CO2 it would take to cause 2 ˚C of warming.

• all
• half
• 10%

Q4. The better place to sequester CO2 is

• deep in the ocean
• underground on land

Q5. Humans have the ability to reduce the temperature of the earth, if we so choose.

• false
• true

Q6. Most of the “low-hanging fruit” of inexpensive carbon emission savings comes from

• new energy sources
• land use management
• energy efficiency

Q7. The “tragedy of the commons” effect arises when an environmental cost is

• internal
• external

Q8. A high discount rate means that the cost of fixing environmental damages seems _ in the future.

• more expensive
• cheaper

Q9. The runaway greenhouse effect as it occurred on Venus is a runaway of

• the Stefan-Boltzmann feedback
• a cloud feedback
• a CO2 weathering feedback
• the water vapor feedback
• the ice albedo feedback

Q10. The total IR energy flux from an object can be measured in units of

• Kelvins
• Watts / m2
• calories
• Joules

Q11. Aerosols _ the Earth.

• cool
• warm

Q12. Which of the following tends to have the stronger cooling effect on Earth’s climate?

• high clouds
• low clouds

Q13. The annual cycle in atmospheric CO2 concentrations arises from interactions between the atmosphere and the

• solid earth
• oceans
• land surface

Q14. What is the approximate rate of atmospheric CO2 emissions from volcanoes?

• 1 Gton C / year
• 100 Gton C / year
• 10 Gton C / year
• 0.1 Gton C / year
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