Experiments with the Model
Video: Energy Emissions Activity (5:32)
Here's the control panel for the model that we will be working with in this exercise, which combines global energy and emissions along with the global carbon cycle model and a global climate model. It's a big, complicated thing but there are just a few controls here you need to know about. They are in kind of different colors here, sectors to kind of control, coal, and oil, and natural gas down in here. This is where we can control the per capita energy history over time, and this is where we can control the population limit that's eventually reached, and this up here, this slider, is the starting time, when some change to reduce the amount of coal oil or gas we use is implemented.
So let me show you how this works. If you just run this the way it comes, without making any changes, you see this. It tells us the total emissions. This is in Gigatons of carbon per year globally, and it shows that going up like this over time, right. Now if I click on the next page, you'll see that in in reality, at this time here, about 2164, we would actually run out of fossil fuels. Here's the fossil fuel reservoir. It's dropping, dropping dropping, gets to zero. At that point, we can't put any more carbon in the air because we don't have any more of these fossil fuels. But this graph here, page 1, shows what we would emit if we could, if we could actually tap into that amount. Anyway, we'll be looking at both of these graphs a little bit.
Let me show you how this works. If we want to say, let's try to reduce the amount of our energy that's supplied by coal. So we switch to that. And this is the coal reduction time. So beginning in the year 2020, and for the next 30 years, we're gonna reduce coal by let's say, let's reduce it by 10%. So currently coal, if you look at this, it's making up 27% of our mix of energy sources. So if we reduce it by 10, then it'll be making up 17. Now the 10 that we reduced coal by is going to add to the renewables down in here, which is currently 0.19. So this is a whole bunch of things, hydro, solar, wind, nuclear, biomass, all lumped together. So if we take from one of these fossil fuel sources, we're going to add it to the renewables here.
So let's implement this change, see what happens. There we go. See we've brought the emissions down quite a bit, and in this case let's see, we don't run out of fossil fuels for a little bit later here. So let's see if we get it so we don't run out of fossil fuels. Let’s reduce the amount of oil we use by 10 percent. See if that does it, And yeah, we just run out at the very, very end here. Ok, so you see what happens there.
Now this is this is connected to a global carbon cycle model. The fossil fuels is part of that. It's also connected to a climate model, so if we were to click through all these different pages in the graph pad, you can see all these little parameters plotted here. Here's the global temperature change and we see that we have increased the temperature by about six and a half degrees by the year 2020, out in here. So 2100 is in here. 2010 is our starting time here. So if we turn these switches off, then we are not going to restrict our use of fossil fuels for an energy source, and we'll just continue with this this mix that's indicated here, the initial fractions. Now there are a couple of other things that you can change here. You can change the population limit by moving this dial around, more or less people, 12 is sort of the default value. You can also change the per capita energy graph here. So if you look at that, this actually is a little funny, it goes from the year 2010 right here. Let's call it the present. And this line over here, this vertical line is the year 2200. So there are 5 divisions in there for about 190 years. So each one those is 38 years. So this vertical line here is the year 2048 and and so on. You just keep adding 38 years to figure out which time each of those vertical lines corresponds to.
You can change this graph. It starts off at 74, and what we're assuming is that it’s going up, at its kind of current pace, but then it levels off up here eventually, by the end of this. But you could take a more optimistic view and say, well we're going to become more conservative in our use of energy and more efficient, and we'll reduce it to a lower level and we can follow a trajectory like that. And you hit okay, and then that will be implemented and you'll see what effect that does. You can undo that change by clicking on this U down here. And let's say you've made a lot of changes and you've made a lot of graphs, you can reset the graphs, or you can restore all the devices to their kind of default values here. All right, so that's it. Have fun with it.
- In this exercise, we will work with a model of a system that has many parts — carbon cycle, climate model, population model, and energy model. We'll explore how making changes to one part of this system alter the behavior of other parts of the system. This illustrates an important part of what we call Systems Thinking, which is that in complex, connected systems, a change in one part may have consequences that spread throughout the system.
- After watching the movie above, run the model without making any changes to establish what we will call the “control” case for these experiments. You can return to this control case by hitting the Restore All Devices button.
- Write down the Total Emissions at the year 2100 — this will be our comparison point in time for later experiments.Look at page 2 of the graph pad, which shows human emissions, which is essentially the same as Total Emissions except that it is limited by the total amount of fossil fuel carbon we have; if we burn through all that carbon, human emissions will drop to 0, and in fact, you’ll see that it drops off to zero about the year 2165 — this is when we run out of fossil fuels. So if we haven’t solved our energy problems by then, we’re in deep trouble!
|switch to turn on||coal||oil|
|f reduction time||20||20|
The table above gives you a set of instructions related to the practice and graded versions of the summative assessment, including which switch to turn on, the fractional reduction, and the time over which this reduction takes place. As one of the fossil fuel sources is reduced, the model increases the renewable fraction so that the total of all the fractions stays at 1.0.
1. How much does switching from one of the fossil fuel sources to renewables decrease the emissions in the year 2100? First, run the model as is when you open it (all switches are in the off position) and take note of the total emissions for the year 2100 on graph #1 (this is our control case), then make the changes prescribed in the table above and find the new emissions in the year 2100 and then calculate the difference from the control case.
Difference = (±2 Gt)
Practice Answer = 11.3
Video: Module 8 Question 1 (1:39)
For the first problem, we are going to see what happens if we completely eliminate our use of oil. And, so to do this problem, first, we just run the control version. So we hit run and it shows us those results, that's with all the switches in the off position. Now we are going to turn the oil switch on. We are going to turn f oil new to zero. That means oil, after the adjustment, will represent zero of our energy, so that completely eliminates it. And remember the renewable fraction will rise as a result of that. We have to make sure that the start time is at 2020, the adjust time is at two. We don't change the per capita energy or the population limit and we run the model again now. And we see a different result here. Now we are going to look at page two. This shows the total emissions and this is what we are interested in. We want to find the total emissions in 2100 and how they differ. So I slide the cursor along back and forth here until I get to 2100 and that is right there. And I see that in run one, that's our control, it was 29.57 of gigatons of carbon emitted. And then in run two, it is down to 19.78, and so it's a difference of 9.79. And that is the answer that we are looking for, the difference, the reduction, basically the distance between the blue curve and this dotted red one here.
2. Does this change lead to a leveling off of emissions, or do they continue to climb?
a) Levels off
b) Continues to climb [correct answer for practice version]
3. Which has a bigger impact in reducing emissions — limiting population growth to 10 billion, or reducing your fossil fuel fractions as prescribed? Here, make sure all the switches are turned off, and then set the Pop Limit to 10.
a) Population limitation
b) Fossil fuel reduction [correct answer for practice version]
Video: Module 8 Question 3 (1:10)
For question 3, we are going to see whether or not reducing oil entirely, or reducing the population, has a bigger effect on the total emissions by the year 2100. So we have already done the case where we reduced oil. Completely cut it out. So now we are going to look at the alternative. So we turn that switch off and get the population down to 10, that's the population limit. Then we run the model again and we see in this kind of pink dashed line here, that's the emissions that pertains to this case, where the population limit is 10. You can see that right away the distance between the dashed pink curve here and the blue one is less than the difference between the blue and the dashed red. So, cutting out oil entirely has a bigger effect in reducing emissions than limiting the population growth to 10 billion.
Reset the Pop Limit to 12 when you are done with this one.
4. How much does reducing all of the fossil fuel sources to a fraction of 0.05 decrease the emissions in the year 2100 compared to the control case (set all switches to the off position for the control)? Set the start time to 2020, then turn on all the switches, and set the f reductions so that each fossil fuel source ends up at 0.05 after 30 years. You can check to make sure you’ve done this correctly by looking at the fractions on page 4 of the graph pad.
Set all of the reduction times to 20 years. For the graded version, lower the fossil fuel sources to a fraction of 0.1; leave everything else the same as the practice version.
Difference = (±2 Gt)
Practice Answer = 23.8
Follow these steps:
- Run the control case (don’t make any changes to the model)
- Turn on all the switches
- Set all the reduction times to 20
- Set f coal reduction to 0.22; f oil reduction to 0.28; f gas reduction to 0.16
- Run the model again — you should now see a blue curve from the control run and a pink curve from the modified run (looking at graph #1)
- Run the cursor along the control case curve until you get to the year 2100 and write down the total emissions at that point — it should be 29.57 (the units are Gt C/yr).
- Run the cursor along the modified case curve (pink one) until you get to the year 2100 and write down the total emissions at that point — it should be 5.74.
- The question is asking for the difference in emissions, so subtract 5.74 from 29.57 and you get 23.83 Gt C/yr — this is the reduction in emissions we would achieve if we lowered all of the fossil fuels to just 5% of our total energy consumption.
Video: Module 8 Question 4 (1:33)
For question number 4 we're going to look at what happens if we drastically reduce all of the different fossil fuel energy sources. So we're going to turn on, well first we'll do the control run, so we run that and see what the emissions are now. We are going to follow the instructions here and turn on all the coal, oil, and gas switches and were going to reduce them all to a new fraction of .05, that's 5%. So each one of them will make up 5% of our total energy sources. Then we're not going to change per capita energy, population limit at 12, start time for reduction at 2020, and adjust time is two years. So we do that, and run the model, and we see results here greatly reduced emissions. So that in 2100, we've got 5.74 gigatons of carbon removed. And so you just subtract 5.74 from 29.57 to get the answer. Which is going to be 23 point something. So that is the answer for that.
5. Which has the bigger impact in reducing emissions — halting the rise in per capita energy use, or reducing our fossil fuel fractions? For this one, you’ll use your answer to the above question (#4) and compare to one in which you turn off all the switches, and then change the per capita energy graph so that it is more or less a straight line all the way across. You can check to see how well you’ve done this by looking at page 8 of the graph pad after you run the model. So, which has a bigger impact in reducing emissions?
a) Fossil fuel reduction [correct answer for practice version]
b) Per capita energy change (i.e., conservation + efficiency)
Video: Module 8 Question 5 (1:50)
For question number 5 we are going to see how the emissions reductions that we get from reducing the reliance on fossil fuels dramatically compares to reducing the per capita energy demand instead. So, this shows results from question 4. So, this was when we set all the fractions to 5% or 0.05 for coal, oil, and gas. But we kept the per capita energy graph, in its starting form, here. Now, what we are going to do is just to turn off those switches. So, we are not going do anything in terms of reducing fossil fuels, but we are going to become more efficient in terms of our energy use. And so, we want to have basically a straight line across here. So, I am just going to try to approximate. You do not have to be to precise about this but there, that is more or less a straight line all the way across. So per capita energy will not increase, it will stay the same per person as we go thru time. So, you hit okay and then run the model again. We see the resulting emissions curve, and you can see that it is higher than what we got for reducing fossil fuels. This particular reduction, or at least no growth per capita energy demand, didn’t give us as big of a result in terms of emission reductions in the year 2100 as the fossil fuel reduction scenario. So that is the answer to this question.
Note: These are pretty drastic changes that we’ve just imposed — they would require nearly miraculous social, political, and technological feats. But, it is good to get a sense of what the limits are.
This table refers to the question below — it provides a set of model settings that lead to stabilization of emissions.
|switches on||coal, oil||all|
|f reduction coal||0.12||0.10|
|f reduction time coal||200||200|
|f reduction oil||0.10||0.07|
|f reduction time oil||100||200|
|f reduction gas||0||0.05|
|f reduction time gas||20||200|
|Per capita energy limit||75 for the whole time||100@2048, then steady at 100 for the rest of the time|
Refer to the worksheet to see what your per capita energy graphs should look like for the practice and graded versions.
6. One of the main goals people mention in the context of future global warming is halting the growth of our emissions of CO2. As you have seen so far, there are a variety of ways to reduce that growth. Now, let’s see what happens when we stabilize emissions. Modify the original model to create the emissions scenario defined by the parameters supplied in the table above — this should result in an emissions history that more or less stabilizes. Then find the emissions in the year 2100.
Total Emissions in 2100 = ±2.0 Gt C/yr
Practice version — 11.3 Gt C/yr
7. Now that you have an emissions scenario that stabilizes (the human emissions of carbon remain more or less constant over most of the time), let’s look at temperature (page 9 of the graph pad). Remember that global temperature change in this model is the warming relative to the pre-industrial world, which is already about 1°C in 2010, the starting time for our model. What is the global temperature change in the year 2100?
Global temperature change = ±0.5 °C
Practice version — 2.6°C
8. Now study the temperature change (graph#9) and the pCO2 atm (the atmospheric concentration of CO2 in ppm or parts per million — page 10 of the graph pad) for the time period following the stabilization of emissions. Does the stabilization of emissions lead to a stabilization of temperature or atmospheric CO2 concentration?
a) both stabilize
b) neither stabilizes — both increase [correct answer for practice]
c) neither stabilizes — both decrease
d) CO2 goes up; temperature goes down
e) CO2 goes down; temperature goes up
Video: Module 8 Questions 6 through 8 (4:13)
Questions 6, 7, and 8 all have to do with a model scenario in which we get the total emissions of carbon to more or less stabilize for a good part of the model run. So, to do this experiment we will first run the basic model control version, so just hit the run button. Then we follow the instructions in the question to set it up to get a scenario where the emissions more or less stabilize. So, to do that we turn on all the switches. We are going to set the new fraction to 0.15, that would be15% for each of these, so that is a decent reduction to our reliance on fossil fuels. We are going to make the transition to be a little slower, so we will move the adjust time to ten. And then we're going to change the per capita energy history. Normally when you open this, you just see this graph. If you click on the table here, you see individual entries. And we are going to alter this as follows: 74 there, 72, and this is 70. This is going to be 67, and 64, and 61. This is just another way to alter that graph. So hit OK. And you see that the graph is declining slightly over time. Keep the population limit at 10. Ok. That’s 11, we’ll make it 10. There we go. Now, we’ll run the model and you see that give us this emissions history that more or less stable. So that is staying the same, and you can see what the emissions are in the year 2100. Gets us down to 6.14 gigatons of carbon in the year 2100. Now what kind of a temperature change can that cause? That is question number 7. So, we look on page 3of the graph pad here, so the temperature change in the year 2100 is1.91 degrees, as opposed to3.92 for the control version. So that is your answer to number 7.
Then number 8 asks this question. So, we stabilize the emissions, does the temperature stabilize and the CO2 concentration in the atmosphere? Well you can see right away that the temperature does not stabilize, it continues to rise, it is just not rising as fast as this control case here. So, to look at the pCO2, we go to page 9 of the graph pad here. There you see the CO2 concentration in the atmosphere starts off at about 400, or a little bit less than that in 2010, and by the time you get to 2100, we have a CO2 concentration in the atmosphere, in this altered version of 484, and that is parts per million, as opposed to 851 in the control version. But look even the CO2 concentration, that does not stabilize either, that continues to go up. So, it is not enough to just stabilize carbon emissions, clearly we need to actually get them to reduce if we want to bring the CO2 concentration down to a lower level and kind of keep it sable. And if we do that, CO2 concentration and temperature are very closely linked together in this model, so they’ll generally do more or less the same thing.
Reset the model before going to the next question.
9. Now, let’s say we want to keep the warming to less than 2°C, which the IPCC recently decided was a good target — warming more than that will result in damages that would be difficult to manage (we would survive, but it might not be pretty). We have seen by now that it is simply not enough to stabilize emissions at a level similar to or greater than today’s — that leads to continued warming. So we need to reduce emissions relative to our present level, which will be hard with a growing population and economy (and thus a growing per capita energy demand).
So, let’s see what is necessary to stay under that 2° limit, given some constraints. In all cases, we’ll assume that we can get our oil and gas fractions down to 0.1 (i.e., 10% each) over a time period of 30 years with a start time of 2020. We’ll leave population out of it (keep the limit at 12 billion), and for the practice version, we’ll make the assumption that per capita energy demand remains constant at a level of 75 for the whole time period (modify the graph so that it is a horizontal line at a level of 75 on the y-axis). This leaves f coal reduction as our main variable. The time period for reducing coal will be 30 years. You can change four scenarios for coal reduction as follows:
A: Keep the coal fraction unchanged (switch off)
B: Reduce the coal fraction to 10% (so f coal reduction would be .17)
C: Reduce the coal fraction to 5% (set f coal reduction to .22)
D: Reduce the coal fraction to 0% (set f coal reduction to .27)
For the graded version, we will change the per capita energy demand graph so that it drops to 50 by the year 2086 (see worksheet for a picture of what the graph should look like).
Find the coal fraction that keeps the temperature closest to 2°C by the year 2200.
Coal reduction scenario (A,B,C, or D):
Practice version: D is the correct answer
Video: Module 8 Question 9 (1:53)
For question 9, we are going to see what needs to be done in terms of reducing the coal fraction to keep the temperature below a two-degree limit by the year 2200. So initially I am just going to restore everything to the starting conditions here. Then we will run it once and see what happens, there we have got the very high temperature change. Now we are going to follow the instructions for setting up the model. We are going to set the start time to 2030. Where going to set the adjust time to 10. We are going to turn on the oil switch and the gas switch. And we are going to keep the per capita energy at 74 the whole way across. So, we do it like this, the same thing we have done before. Hit okay. So, there we have that set. We are going to set the f oil new (new oil fraction) to 0.1 and do the same with gas. So, we reduced those two to 10%, .10. Then we have the population limit set at 12, so that is good. Now we are going to explore 4 different scenarios and in each scenario we are going to do something different with the coal. The first one we are going to keep the coal fraction unchanged, so we have the switch off, and we run it. We see what the temperature is, and by the end we are at 3.59 degrees is the temperature change. So that is not acceptable. So that one does not do it so we will try scenario B. So, we turn the coal switch on and we then reduce the f coal new to .1 and run it. So lower temperature, we are using less coal, but we are still at 2.66 so that is too high. Now we will change f coal new to .05 and run it again. And we see we are still up here at 2.36. So, we are still above two. Now let’s see what happens if we eliminate coal entirely, move it to zero and run it again. And here we are, and at that point we have still a temperature of 2.05, so that one is very close, but it still does not get us quite below that 2 degree limit. I So, in this case, none of those case scenarios works right and that is one of the choices in the question is that none of these above scenarios keeps the temperature below 2 degrees. The last one comes close but it still does not quit get there.
We’re done with this model for now, but you will be coming back to something similar to this later on when you do your capstone projects. You’ll use the model to design an emissions and energy consumption scenario for the future for which you’ll also explore the environmental and economic consequences.
The following questions encourage you to step back and think about what you’ve learned here. Short answers will suffice here.
10. What are the three principal variables that determine how much carbon is emitted from our production of energy? (Hint: look at page 11 of this worksheet)
11. What is the relationship between economic development (growth) and per capita energy consumption? (Hint: look at figure 7 of this worksheet)
12. Among the various sources of our energy, which has the highest rate of CO2 emitted per unit of energy? (Hint: look at table on page 10 of this worksheet)
13. What happens to the atmospheric concentration of CO2, and thus the global temperature, if we stabilize (hold constant) the emissions rate? (refer to question #8 above)
14. Can we stay under the 2°C warming limit in the year 2200 by completely eliminating our reliance on fossil fuel energy sources alone (reducing coal, oil, and gas to 0% of our energy supply), or do we also need to reduce our energy consumption per capita? (make appropriate changes and then run the model to figure this out)