After completing your Summative Assessment, don't forget to take the Module 8 Quiz. If you didn't answer the Learning Checkpoint questions, take a few minutes to complete them now. They will help your study for the quiz and you may even see a few of those question on the quiz!
In this activity, we will explore the relationships between global population, energy consumption, carbon emissions, and the future of climate. The primary goal is to understand what it will take to get us to a sustainable future. We will see that there is a chain of causality here — the future of climate depends on the future of carbon emissions, which depends on the global demand for energy, which in turn depends on the global population. Obviously, controlling global population is one way to limit carbon emissions and thus avoid dangerous climate change, but there are other options too — we can affect the carbon emissions by limiting the per capita (per person) demand for energy through improved efficiencies and by producing more of our energy from “greener” sources. By exploring these relationships in a computer model, we can learn what kinds of changes are needed to limit the amount of global warming in the next few centuries.
Read the activity text and then run the experiments using the directions given on the downloadable worksheet below (also repeated here in the following pages). We recommend that you download the worksheet and follow it, writing down your answers as you go through the exercise. But first, view the video at the top of the "Experimenting With The Model" page, linked to below. You will then need enter your answers in the summative assessment.
Download worksheet [1]to use when submitting your assignment
Once you have answered all of the questions on the worksheet, go Module 8 Summative Assessment (Graded). The questions listed in the worksheet will be repeated as a Canvas Assessment. So all you will have to do is read the question and select the answer that you have on your worksheet. You should not need much time to submit your answers since all of the work should be done prior to clicking the assessment quiz.
This assignment is worth a total of 19 points. The grading of the questions and problems is below:
Item | Possible Points |
---|---|
Questions 1-9 | 1 point |
Questions 10-14 | 2 points |
Before going ahead, we need to make sure we all have a clear picture of the various units we use to measure energy.
Joule — the joule (J) is the basic unit of energy, work done, or heat in the SI system of units; it is defined as the amount of energy, or work done, in applying a force of one Newton over a distance of one meter. One way to think of this is as the energy needed to lift a small apple (about 100 g) one meter. An average person gives off about 60 J per second in the form of heat. We are going to be talking about very large amounts of energy, so we need to know about some terms that are used to describe larger sums of energy:
Exponential notation | Scientific Notation | Abbreviation | Unit name |
---|---|---|---|
103J | 1e3 J | kJ | kilojoule |
106J | 1e6 J | MJ | megajoule |
109J | 1e9 J | GJ | gigajoule |
1012J | 1e12 J | TJ | terajoule |
1015J | 1e15 J | PJ | petajoule |
1018J | 1e18 J | EJ | exajoule |
1021J | 1e21 J | ZJ | zettajoule |
1024J | 1e24 J | YJ | yottajoule |
In recent years, we humans have consumed about 518 EJ of energy per year, which is something like 74 GJ per person per year.
British Thermal Unit— the btu is another unit of energy that you might run into. One btu is the amount of energy needed to warm one pound of water one °F. One btu is equal to about 1055 joules of energy. Oddly, some branches of our government still use the btu as a measure of energy.
Watt— the watt (W) is a measure of power and is closely related to the Joule; it is the rate of energy flow, or joules/second. For instance, a 40 W light bulb uses 40 joules of energy per second, and the average sunlight on the surface of Earth delivers 343 W over every square meter of the surface.
Kilowatt hours— when you (or you parents maybe for now) pay the electric bill each month, you get charged according to how much energy you used, and they express this in the form of kilowatt hours — kWh. If you use 1000 Watts for one hour, then you have used one kWh. This is really a unit of energy, not power:
In other words, one kilowatt hour is 1000 joules per second (kW) summed up over one hour (3600 seconds), which is the same as 3.6 MJ or 3.6 x 106J or 3.6e6 J.
The energy we use to support the whole range of human activities comes from a variety of sources, but as you all know, fossil fuels (coal, oil, and natural gas) currently provide the majority of our energy on a global basis, supplying about 81% of the energy we use:
The non-fossil fuel sources include nuclear, hydro (dams with electrical turbines attached to the outflow), solar (both photovoltaic and solar thermal), and a variety of other sources. These non-fossil fuel sources currently supply about 19% of the total energy.
The percentages of our energy provided by these different sources have clearly changed over time and will certainly change in the future as well. The graph below gives us some sense of how dramatically things have changed over the past 210 years:
There are a couple of interesting features to point out about this graph. For one, note that the total amount of energy consumed has risen dramatically over time — this is undoubtedly related to both population growth and the industrial revolution. The second point is that shifting from one energy source to another takes a long time. Oil was being pumped out of the ground in 1860, and even though it has a greater energy density and is more versatile than coal, it did not really make its mark as an energy source until about 1920, and it did not surpass coal as an energy source until about 1940. Of course, you might argue that the world changed more slowly back then, but it is probably hard to avoid the conclusion that our energy supply system has a lot of inertia, resulting in sluggish change.
We are all aware of some of the ways we use energy — heating and cooling our homes, transporting ourselves via car, bus, train, or plane — but there are many other uses of energy that we tend not to think about. For instance, growing food and getting it onto your plate uses energy — think of the farming equipment, the food processing plant, the transportation to your local store. Or, think of manufactured items — to make something like a car requires energy to extract the raw materials from the earth and then assembling them requires a great deal of energy. So, when you consider all of the different uses of energy, we see a dominance of industrial uses:
Since we are going to be modeling the future of global energy consumption, we should first familiarize ourselves with the recent history of energy consumption.
Here, we will explore a few possibilities, the first of which is global population increase — more people on the planet leads to a greater total energy consumption. To evaluate this, we need to plot the global population and the total energy consumption on the same graph to see if the rise in population matches the rise in energy consumption.
The two curves match very closely, suggesting that population increase is certainly one of the main reasons for the rise in energy consumption. But is it as simple as that — more people equals more energy consumption?
If the rise in global energy consumption is due entirely to population increase, then there should be a constant amount of energy consumed per person — this is called the per capita energy consumption. To get the per capita energy consumption, we just need to divide the total energy by the population (in billions) — so we’ll end up with Exajoules of energy per billion people.
Today, we use about 3 times as much energy per person than in 1900, which is not such a surprise if you consider that we have many more sources of energy available to us now compared to 1900. Note that at the same time that the population really takes off (see Fig. 5), the per capita energy consumption also begins to rise. This means that the total global energy consumption rises due to both the population and the demand per person for more energy.
Let’s try to understand this per capita energy consumption a bit better. We know that the global average is 74 EJ per billion people, but how does this value change from place to place? There are some huge variations across the globe — Afghans use about 4 GJ per person per year, while Icelanders use 709 GJ per person. Why does it vary so much? Is it due to the level of economic development, or the availability of energy, or the culture, or the climate? You can come up with reasons why each of these factors (and others) might be important, but let’s examine one in more detail — the economic development expressed as the GDP (the gross domestic product, which reflects the size of the economy) per capita.
The obvious linear trend to these data suggests that per capita energy consumption is a function of GDP, while the fact that it is not a tight line tells us that GDP is not the whole story in terms of explaining the differences in energy consumption. Not surprisingly, we are near the upper right of this plot, consuming more than 300 GJ per person per year. Iceland’s economy is not as big per person as ours and yet they consume vast amounts of energy per person, partly because it is cold and they have big heating demands, but also because they have abundant, inexpensive geothermal energy thanks to the fact that they live on a huge volcano. Many European countries with strong economies (e.g., Germany) use far less energy per person than we do (168 GJ compared to our 301 GJ), in part because they are more efficient than us and in part because they are smaller, which cuts down on their transportation. A big part of the reason they are more efficient than us is that energy costs more over there — for instance, a gallon of gas in Italy is about $8. Our neighbor, Mexico, has a per capita energy consumption that is just about the global average.
Pay attention to the two red squares in Fig. 7 — these show the global averages in terms of GDP and energy consumption per person for two points in time. The trend is most definitely towards increasing GDP (meaning increasing economic development) and increasing energy consumption per person. Economic development is definitely a good thing because it is tied to all sorts of indicators of a higher quality of life — better education, better health care, better diet, increased life expectancy, and lower birth rates. But, economic growth has historically come with higher energy consumption, and that means higher carbon emissions.
Now that we’ve seen what some of the patterns and trends are, we are ready to think about the future.
There are many ways to meet our energy demands for the future, and each way could include different choices about how much of each energy source we will need. We’re going to refer to these “ways” as scenarios — hypothetical descriptions of our energy future. Each scenario could also include assumptions about how the population will change, how the economy will grow, how much effort we put into developing new technologies and conservation strategies. Each scenario can be used to generate a history of emissions of CO2, and then we can plug that into a climate model to see the consequences of each scenario.
The global emission of carbon into the atmosphere due to human activities is dominated by the combustion of fossil fuels in the generation of energy, but the various energy sources — coal, oil, and gas — emit different amounts of CO2 per unit of energy generated. Coal releases the most CO2 per unit of energy generated during combustion — about 103.7 g CO2 per MJ (106 J) of energy. Oil follows with 65.7 g CO2/MJ, and gas is the “cleanest” or most efficient of these, releasing about 62.2 g CO2/MJ.
At first, you might think that renewable or non-fossil fuel sources of energy will not generate any carbon emissions, but in reality, there are some emissions related to obtaining our energy from these means. For example, a nuclear power plant requires huge quantities of cement, the production of which releases CO2 into the atmosphere. The manufacture of solar panels requires energy as well and so there are emissions related to that process because our current industrial world gets most of its energy from fossil fuels. For these energy sources, the emissions per unit of energy are generally estimated using a lifetime approach — if you emitted 1000 g of CO2 to make a solar panel and over its lifetime, it generated 500 MJ, then it’s emission rate is 2 g CO2/MJ. If we average these non-fossil fuel sources together, they release about 5 g CO2/MJ — far cleaner than the other energy sources, but not perfectly clean.
So, to sum it up, here is a ranking of the emissions related to different energy sources:
Energy Source | g CO2 per MJ |
---|---|
Coal | 103.7 |
Oil | 65.7 |
Gas | 62.2 |
Non-Fossil Fuel* | 6.2** |
*Hydro, Nuclear, Wind, Solar
**This will decrease as the non-fossil fuel fraction increases
Our recent energy consumption is about 518 EJ (1018 J). Let’s calculate the emissions of CO2 caused by this energy consumption, given the values for CO2/MJ given above and the current proportions of energy sources — 33% oil, 27% coal, 21% gas, and 19% other non-fossil fuel sources. The way to do this is to first figure out how many grams of CO2 are emitted per MJ given this mix of fuel sources and then scale up from 1 MJ to 518 EJ. Let’s look at an example of how to do the math here — let r1-4 in the equation below be the rates of CO2 emission per MJ given above, and let f1-4 be the fractions of different fuels given above. So r1 could be the rate for oil (65.7) and f1 would be the fraction of oil (.33). You can get the composite rate from:
Plugging in the numbers, we get:
What is the total amount of CO2 emitted? We want the answer to be in Gigatons — that’s a billion tons, and in the metric system, one ton is 1000 kg (1e6 g or 106 g), which means that 1Gt = 1015 g (1e15 g).
So, the result is 31.8 Gt of CO2, which is very close to recent estimates for global emissions.
It is more common to see the emissions expressed as Gt of just C, not CO2, and we can easily convert the above by multiplying it by the atomic weight of carbon divided by the molecular weight of CO2, as follows:
And remember that this is the annual rate of emission.
Let’s quickly review what went into this calculation. We started with the annual global energy consumption at the present, which we can think of as being the product of the global population times the per capita energy consumption. Then we calculated the amount of CO2 emitted per MJ of energy, based on different fractions of coal, oil, gas, and non-fossil energy sources — this is the emissions rate. Multiplying the emissions rate times the total energy consumed then gives us the global emissions of either CO2 or just C.
We now see what is required to create an emissions scenario:
In this list, the first three are variables — the 4th is just a matter of chemistry. So, the first three constitute the three principal controls on carbon emissions.
Here is a diagram of a simple model that will allow us to set up emissions scenarios for the future:
In this model [2], the per capita energy (a graph that you can change) is multiplied by the Population to give the global energy consumption, which is then multiplied by RC (the composite emissions rate) to give Total Emissions. Just as we saw in the sample calculation above, RC is a function of the fractions and emissions rates for the various sources. Note that the non-fossil fuel energy sources (nuclear, solar, wind, hydro, geothermal, etc.) are all lumped into a category called renew, because they are mostly renewable. The model includes a set of additional converters (circles) that allow you to change the proportional contributions from the different energy sources during the model run.
This emissions model is actually part of a much larger model that includes a global carbon cycle model and a climate model. Here is how it works — the Total Emissions transfers carbon from a reservoir called Fossil Fuels that represents all the Gigatons of carbon stored in oil, gas, and coal (they add up to 5000 Gt) into the atmosphere. Some of the carbon stays in the atmosphere, but the majority of it goes into plants, soil, and the oceans, cycling around between the reservoirs indicated below. The amount of carbon that stays in the atmosphere then determines the greenhouse forcing that affects the global temperature — you’ve already seen the climate model part of this. The carbon cycle part of the model is complicated, but it is a good one in the sense that if we plug in the known historical record of carbon emissions, it gives us the known historical CO2 concentrations of the atmosphere. Here is a highly schematic version of the model:
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.
Practice | Graded | |
---|---|---|
switch to turn on | coal | oil |
f reduction | 0.24 | 0.30 |
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
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]
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:
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)
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.
Practice | Graded | |
---|---|---|
switches on | coal, oil | all |
start time | 2020 | 2050 |
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 |
Pop Limit | 12 | 11 |
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
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
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)