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Click here to go to the model.

When you open the model, you will see that there are a lot of controls, reflecting the full range of choices we can make about our future energy consumption and geoengineering. There are also 15 pages of graphs that show the results of the model. Be sure to watch the video below that introduces you to the model before proceeding.

Video: Module 12 Intro to Model (7:09)

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Click here for a transcript of the Module 12 Intro to Model video.
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This is the model that we're going to be working with in this lab, and it's similar to one you've seen before, that combines a global carbon cycle with a global climate model. And it includes components that calculate our energy needs and our sources of energy, which then relate to the carbon emissions that affect the climate. It also monitors the economics of all these changes to our climate and energy. This one also includes some geoengineering options that I'll explain in a little bit.

So, over here there are a lot of controls. They're kind of color-coded according to the different things that they represent. So, green here represents conservation of energy. The purple or blue represents renewable energy. The red down here relates to one of the geoengineering schemes, which is the direct carbon removal from the atmosphere. And the orange down here deals with the other geoengineering scheme, which is the injection of sulfate aerosols into the stratosphere to block sunlight.

So, let me just show you a couple things about this. So, you open the model and you run it and it calculates this all out over a couple of hundred years. And this shows the global temperature change that results, and here we haven't really done anything to increase conservation or renewables, and the geoengineering switches are off, so this is kind of a do-nothing scenario. We have a very high temperature rise by the end of this time here, six and a half degrees warmer. So now, we could say, of course, well what if we conserve energy? So, this number here is the percent of our energy that we reduce by conservation methods. And this is the growth rate of that. So, this is five percent increase per year, which is pretty good. So, if we run this and see what happens and compare it with the do nothing scenario, you see it lowers the temperature, but it's still unacceptably high. And so, you could say, well what if we increase our reliance on renewable energy? Let's bring this up to say seventy-five percent and we run that, and we see that this does a little bit better. But still, by the end of this, look, we're up at three point six degrees of global temperature rise, which is really quite alarming and by the year 2000 we're, 2100 rather, we’re above that 2 degree limit that we sort of agreed upon as the upper limit in the Paris Climate Accords.

So now, we've added here some geoengineering options and these are kind of like, if we just can't manage our carbon emissions for conservation and switch to renewables, we might want to investigate some of these to help us prevent this climate disaster. And so, I'm gonna restore the renewables to where it was before. I'll just turn this on, so now, this is going to activate the direct removal of carbon from the atmosphere and then the burial and sequestration of that carbon underground. So, here's the time at which it starts, 2030, and in here you pick a target atmospheric CO2 concentration. So, here, I've got 400. Let’s raise that to 450 here. And this is the rate of cost decline of that process, which is initially fairly expensive. And this represents how quickly our capability to do this grows. And this gives us the initial amount of carbon that we can withdraw from the atmosphere in one year, at the very start. So, this is pretty generous because it can't really come close to doing one gigaton at the present time, but things are changing rapidly in this field. So, let's see what happens here. And we run this, and we see here's our result. Look, this brings us down, keeps us below two degrees for a fairly long time. So that is a fairly effective means of keeping our climate under control. If I switch on some of these other pages, you'll see that this, the blue is the CO2 concentration in the atmosphere, rises and then we start to get it in control and then we've brought it under control here, it's close to 450, it’s a little bit above. Until this point in time, in which it drops down dramatically there just because we've run out of fossil fuels, and so we're no longer able to emit any to the atmosphere at this point in time. So 2197 or 98, something like that. So, that's the direct removal of carbon.

Another option is sulfate aerosol geoengineering, and we turn that on. This is where we inject sulfate aerosols, these little tiny particles into the stratosphere. They block some sunlight and so here's the starting time for this process, and here's the targeted temperature change that we're going to try to control to. So, this will try to keep the temperature change to two degrees or less and this is the cost decline rate. I've got this at zero right now, kind of assuming that this is not such a technologically tricky process and probably we're not going to see huge advances in the sort of ability to do this per dollar. So, I've got that at zero initially. Well, let's just run this and see what happens. You run the model, and there you see, this does a very good job of keeping it right at two degrees through this whole time. While all of these changes have economic consequences, and some of those you can see, on some of the other graphs here, let's see this one. Here's the total cost per person, per capita, that is in terms of thousands of dollars per year. And those last two that we ran, they both end up costing something like about $9,000 per person per year by the end of it. And that's to pay for all of our energy supply and all the climate damages that are associated with the temperature change.

So, this is just a brief introduction to the model. You can restore everything to this sort of an initial by clicking those two buttons. And so, we're going to do a series of experiments with this model to make some sort of assessments about what is the best thing, from the standpoint of the climate and also the economy, in terms of getting us to a future that includes a tolerable level of global warming.

Practice Questions

Part A. Climate Control by Conservation and Renewable Energy

Be sure to watch the video below that shows how to do problems 1-3.

Video: Module 12 Questions 1 - 3 (2:01)

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Click here for a transcript of the Module 12 Questions 1-3 video.
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In this video, I'm going to show you how to manipulate the model to get the answers to the first three questions of the practice assessment. So, I'm going to follow the instructions and change the green colored sliders so that this is 30, and this is zero point one. Renewable upper limit, I'm going to change to 85, and the renewable growth rate to zero point one. I've done that. Now, I'm going to run the model. And I'll look at the ending temperature change. So, let's see, it's about two point one three, two point one four at the very end. And so, looking at the choices, the correct answer is two point one degrees C. So, that's answer C on the on the test.

Well, number two is, what is the lowest pH of the oceans in this case? I'm going to have to go to graph page number two. So, here in pink is the pH and it's dropping all the way down to eight point zero six, or eight point zero eight, somewhere in there. So, the closest value and the possible answers is eight point zero eight. So, we'll select that one. So, A is the correct one.

Then, what is the total cost per person? I'm here and it says to click through to page fourteen, so we're gonna skip through all these other plots that show all sorts of other parameters to page 14. This is the total cost per capita in thousands of dollars. And you can see that it rises to two point four thousand per person at the end of the time here. So, that's D. So 3D is answer for that one.

In this first experiment, we will use a combination of conservation of energy and greater reliance on renewable energy sources to limit climate change. Open the model and run it without making any changes — we’ll call this the “do nothing” scenario. You will see that we end up with 6.55°C of warming by the end of the model run in 2210, and if you look through the other graphs, you will see that the ocean pH drops to 7.68 (graph page 2). Looking at some of the other graphs, we see that this scenario results in a bit over 19 thousand dollars per person (graph page 14) in terms of the total costs (energy, conservation, climate damages, geoengineering), and an ending net economic output of about $460 trillion.

Now, change the model as described below:

Green colored sliders

Conserve upper limit: 30

Conserve growth rate: 0.1

Blue colored sliders

Renew upper limit: 85

Renew growth rate: 0.1

Then, run the model and answer the following questions by finding the values from the resulting graphs.

  1. What is the ending global temperature change that results from these changes (page 1)?
    A) 4.2 °C
    B) 3.6 °C
    C) 2.1°C
    D) 1.6°C
     
  2. What is the lowest pH of the oceans in this case (page 2)?
    A) 8.08
    B) 7.6
    C) 8.20
    D) 7.85
     
  3. What is the Total Cost Per Person (page 14)
    A) 12.4
    B) 8.2
    C) 7.7
    D) 2.4

Part B. Climate Control by Geoengineering

Now, we will try geoengineering alternatives, beginning with the direct removal of carbon — DCR. Be sure to watch the video below that shows how to get the answers to problems 4-7.

Video: Module 12 Questions 4-7 (3:08)

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Click here for a transcript of the Module 12 Questions 4-7 video.
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Now we're going to move on and look at how to get the answers to problems 4 through 7, the next section of this assessment. So here I've got to make some new changes. I'm going to cut down the conservation of energy, turn that to 1, and the growth rate stays at .1. The blue sliders are going to change so that the renewable upper limit is 20, all the way down here, and the growth rate is .1. I’m going to turn the DCR, direct carbon removal, switch on. Set the start time to 2030. The target atmospheric concentration, I'm going to set this to 470. The cost decline rate I'm going to make .02, so 2 percent per year decline in the cost of this process. The growth rate in terms of capacity is going to be 2% per year and the initial amount that we can withdraw from the atmosphere is 5 gigatons of carbon. So that's all set according to the instructions. Now I'm going to run it and see what the ending temperature is in this case. And here by the end we see we're down to just below 2, 1.97. So that's answer C.

Then 5 is what is the lowest pH In this case? I’m going to flip to page number 2. Looks like the lowest pH is back in here, that's about 8.06, so that's answer, A.

Then the next one is, what is the total cost per person? So that's page 14 of the graph pad. I'm going to get there this way, there's 14. We see that's up considerably higher now it's 9.2 thousand dollars or 9.2 thousand dollars per person at the at the end of time. So that's answer B.

Now the last question, seven, is why do the human fossil fuel emissions drop to zero around the Year 2095? So if we went back to let's say graph pad number two, you can see the the human fossil fuel burning emissions. This is gigatons of carbons rising, flattening off and then it just crashes, boom, to zero here. And so why is that? Well it turns out that if we cycle through here to page eleven on the graph pad, we see the fossil fuels, so this is in gigatons of carbon. And by the time we get to about 2095 or so we've essentially gone to zero. So we've run out of fossil fuels and so that that's why the emissions dropped is because we've got nothing left to burn. So that's answer C on the assessment.

Make the following changes to the model:

Green colored sliders

Conserve upper limit: 1

Conserve growth rate: 0.1

Blue colored sliders

Renew upper limit: 20

Renew growth rate: 0.1

Red colored sliders

DCR switch: On

DCR start time: 2030

Target atm pCO2: 470

DCR cost decline rate: 0.02

DCR growth rate: 0.02

DCR init: 5

Once you’ve made these changes, run the model and answer the following.

  1. What is the ending global temperature change that results from these changes (page 1)?
    A) 4.2 °C
    B) 2.6 °C
    C) 1.97°C
    D) 3.3°C
     
  2. What is the lowest pH of the oceans in this case (page 2)?
    A) 8.06
    B) 7.6
    C) 8.20
    D) 7.85
     
  3. What is the Total Cost Per Person (page 14)?
    A) 11.2
    B) 9.2
    C) 6.7
    D) 2.4
     
  4. Why do the human FFB emissions drop to 0 around the year 2195?
    A) Our energy needs drop to 0 at this time
    B) The economy has collapsed at this time
    C) We run out of fossil fuels at this time
    D) Must be a glitch in the model

Now we will try sulfate aerosol geoengineering — as before, the following video shows how to do this section.

Video: Module 12 Questions 8 - 9 (1:49)

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Click here for a transcript of the Module 12 Questions 8-9 video.
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In this video, I'm going to show you how to get the answers to Questions 8 & 9 on the assessment. And so, we look at the instructions, and we see that we set the conserve upper limit at 1, its growth rate at 0.1, the renew upper limit at 20, and its growth rate at .1. Make sure the DCR switch is off, and we turn the sulphate switch on, and start time 2030. The target key range is 2, and the sulfate cost decline rate is zero. So, you do those things, and we run it, and you'll see the temperature will flatten off at about two degrees. Once it gets done running here, there we see it, so it stays at just a hair above two degrees throughout the time.

Now Question 8 is, what is the lowest pH of the oceans in this case? So, we go to graph number two, look at the pH curve in pink here, and it drops down to 7.58 here at the low point. So, that's answer D. So, that's correct answer for 8.

Nine is, what is the total cost per person? That's page fourteen, that's the graph page. Go back to page 14 and see the total costs per capita at the end is about 9.3 thousand dollars per person at the very end. So, that's answer B on the assessment and that's the answer.

Make the following changes to the model:

Green colored sliders

Conserve upper limit: 1

Conserve growth rate: 0.1

Blue colored sliders

Renew upper limit: 20

Renew growth rate: 0.1

Red colored sliders

DCR switch: Off

Orange colored sliders

Sulfate switch: On

Sulfate start time: 2030

Target T change: 2.0

Sulfate cost decline rate: 0.0

Once you’ve made these changes, run the model and answer the following.

  1. What is the lowest pH of the oceans in this case (page 2)?
    A) 8.06
    B) 7.6
    C) 8.20
    D) 7.58
     
  2. What is the Total Cost Per Person (page 14)?
    A) 11.2
    B) 9.3
    C) 6.7
    D) 2.4
     

Part C. Comparison

Now, let’s step back and consider what we have found here. Clearly, the “do-nothing” scenario is the worst in terms of temperature change and costs. But how about the other scenarios, each of which gets us to a temperature change of close to 2°C by the end of the model run — which is the best? The following video shows how to answer questions 10-12.

Video: Module 12 Questions 10 - 12 (3:46)

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Click here for a transcript of the Module 12 Questions 10-12 video.
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Today, I'm going to show you how to get the answers to Questions 10 through 12 on the assessment. And this is where we kind of step back and consider all these different options, these three basic options together and compare them. And in the first one, we kept the temperature close to about a two degree warming by the end of the model run, by energy conservation and increased reliance on renewable energy. The next one, we achieved that same temperature level, approximately, through geoengineering and direct carbon removal. And the third case, shown in the blue here, was the sulfate aerosol geoengineering.

And so, the question is for 10, which of these three scenarios is the best from an economic standpoint?There are lots of different ways of looking at the economic performance of each of these three, but I think the one that sort of sums it all up best is this total costs per capita. So, these are costs per person that we're gonna have to pay for producing the energy and the consequences of producing that energy in the form of climate change, or moderating it in terms of geoengineering costs. Then, you can see the two geoengineering cases here are pretty close to the same 9.3, 9.2 thousand. The conservation scenario and renewable energy one is considerably less expensive, so 2.4 thousand per person compared to nine. So, that's the clear winner. So, that's answer A for ten.

Eleven asks which of the three scenarios is best from an ocean pH standpoint? And so, here, we have to look at graph page number two, and these are shown in different scales. This just shows the pH for the last one, the conservation one, and that was at 8.06. And if you remember from before, that's about the same, close to the same, that we got with the DCR geoengineering. So, those two were about the same. Sulfate geoengineering, the ph got down to 7.58 , which is really a pretty dramatic acidification of the ocean. So, that's the worst by far. Conservation and renewables are close to the same. There's not a clear winner. So, the best answer is D, which is A and B are about the same.

And the last question of the assessment, twelve, asks from an overall environmental and economic standpoint, which of the three scenarios is the best? Well, as we saw in terms of ph, the conservation renewables and the dcr geoengineering are about the same. In terms of temperature, they're all more or less the same by the time we get to the the end of time. Although, you know, you could say that the conservation and renewable approach here, kept us at a lower temperature for more of the time, so that might be preferable in that sense. But then, the other thing, the economic standpoint as we saw before, this conservation and renewable scenario, shown here in green, that's the clear winner. So, if you take all these things together the conservation and renewable scenario is the best, overall, from an environmental and economic standpoint. That's answer A on the assessment and that's the correct answer.

  1. Which of the three scenarios is the best from an economic standpoint?
    A) Conservation + Renewables
    B) DCR Geoengineering
    C) Sulfate Geoengineering
     
  2. Which of the three scenarios is the best from an ocean pH standpoint?
    A) Conservation + Renewables (by far)
    B) DCR Geoengineering (by far)
    C) Sulfate Geoengineering (by far)
    D) A and B are about the same
     
  3. From an overall environmental and economic standpoint, which of the three scenarios is the best?
    A) Conservation + Renewables
    B) DCR Geoengineering
    C) Sulfate Geoengineering
    D) There are no clear winners