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Lab 5: Carbon Cycle Modeling

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Lab 3: Climate Modeling

Download this lab workbook as a Word document: Lab 5: Global Carbon Cycling. (Please download required files below.)

Answer the questions below, then enter your answers in the Module 5 Lab 5 Submission. There may be additional questions that are in the Canvas Submission only (not listed below).

This lab is the same format as the lab for Module 4. Answer the questions in the workbook. Then, when you are ready, complete the Module 5 Lab 5 Submission in a timed environment. Make sure you have the model ready to run, as we will be asking additional questions as indicated below.

STEP 1. Please Note: The model in the videos below may look slightly different than the model (linked below) that you will use to complete Step 1. Both models, however, function the same.

Video: Carbon Cycle Intro (4:15)

Click here for a transcript of the carbon cycle intro video.

Hi, everybody, so this is the model that we're going to use in the first part of the lab, and I want you to really familiarize yourself with the controls before you really get started, okay? I think it's really important. And, it can be a lot of fun to experiment with this and really get used to playing with it before you start the lab. And I think if you do that, then the lab will be very straightforward.

So basically, what we have here is a carbon cycle, very complicated. This is the STELLA version of the carbon cycle here, and you can basically see all the knobs and bells and whistles with these STELLA connections. And over on this side is the ocean model that we already used in Module 3 lab. So you really don't need to understand this, of course, but it shows you how complicated it is, and we'll see later on why it's such a good model.

Ok, so the bottom line is we have three different emissions scenarios that are controlled down here by these switches, okay? We have a business as usual (BAU) switch, which is basically the worst case scenario, emission scenario A2. And you can see that is here. It goes all the way up and actually, then it drops off, but still it goes all the way up through 2100. We continue fossil fuel burning through 2100 without stopping. Okay, that's this switch. So that's with this on. And you can read about this down here. So if I turn this switch off and I leave this switch off, and I'll explain this switch in a minute, then what we do is we level off fossil fuel burning around 2010. We just level it off, okay? Which obviously didn't happen because we've gone through 2010. But it just shows you what happens if we slow down fossil fuel burning, don't completely stop it, okay? And then the third switch is what we do is if we all of a sudden drastically stop fossil fuel burning, FFB Halt. And what that shows is that around 2010, we stop. Let's see if I can move this up. But anyway, it's down here. You can see we stop fossil fuel burning at 2010. It goes down to zero. Ok, so that's basically what happens with that third switch.

So the three switches are, the three scenarios are, business as usual (BAU) with this switch on, this switch off. Both switches off, is Leveling Off at 2010. And then with this switch on, we halt fossil fuel burning (FBB) at 2010. Ok, don't worry about the land use switch for this part of the lab.

All right now, the critical thing is we can run, let's run business as usual (BAU). I want to show you one other thing. You run this model here, and let's say you want to then run another model. Let's say we'll turn it off and run the second one. You can see these two curves side by side, so you can see business as usual (BAU), and then you can see the leveling off of fossil fuel burning (FFB). And then if you want to run the third one. Excuse me, sorry about that. We're just going to turn this on. And then you see the third scenario here, 3. So, 1 - business as usual (BAU), 2 - leveling off (Leveling Off), 3 - fossil fuel burning (FFB). But what I wanted to show you also, is that if you want to then start over again and do something different, you restore everything. Okay? In general, it's a good idea between experiments to restore everything, to get everything back to back to usual, back to normal. And then why not?

One other tip that I just thought about is if for some reason the model isn't working for you and you aren't using Google Chrome. Switch to Chrome because it's the most stable. It's the most stable browser for STELLA models.

All right, so let me show you the output that we can get. So let's have business as usual (BAU). This is global temperature change, and as I said, the emissions, the fossil fuel burning stops at 2150, or so. And so you'll see this temperature decrease, which isn't really important for the lab. CO2, you can see it rises steadily here, and then drops here. pH goes down and then rises a little bit, but you can see it's going down. This is ocean pH.

And then one other thing I wanted to show you is make sure you can read the values here. So I'm going to click on the curve and you can see it running along the curve. It shows you the values down on the bottom rung, 8.14987. And then moving down the curve, you can see the values. You can see both the year and the values. So now I'm 2040, and I'm now at 2083, my value is 7.844. And now I'm down at 2040, excuse me, 2153, at the bottom and my value is 7.55. Ok, so make sure that you can run the the cursor along the curve and read the values not only of the year, but the values of pH, temperature, CO2, et cetera. All of these different curves you can do this, which is really, really helpful and very important for the lab. All right? So then we also have how much of the CO2 is absorbed by the air? How much is absorbed by the ocean? How much is absorbed by the biosphere in the purple curve, number 3.

Moving along, page 5 shows you fossil fuel burning, which shuts off as I said earlier, around 2050, or so. This is both CO2 and fossil fuel burning. Fossil fuel burning in red, CO2, atmospheric CO2 total, in blue, comparing those two curves. This here shows you what happens in the biosphere. It's the atmosphere in 1, the land biota in 2. How much CO2 is absorbed by land. How much is absorbed by soil. How much is absorbed by permafrost. And then this here shows how much it's absorbed by surface ocean and deep ocean. This here shows you the gigatons of carbon from fossil fuel burning. And then finally, a comparison of the model and observations.

So this shows you in blue the model run. This is the model run that we have established with this carbon cycle. And in red, we show the observed atmospheric CO2. This is measured in the atmosphere through twenty ten and you can see how close they are together, which shows that this model works really well. All right, so that's a good summary of what this model does. This is for the first part of the lab step one, and I will be producing another video for step two.

To begin with, we will use this model of the carbon cycle (which is coupled to the same climate model we used in Module 3) to learn a few basic things about how the model responds to different scenarios of carbon emissions from fossil fuel burning (FFB). Note, the A2 scenario is also known as “Business-as-Usual” (BAU) in which we make no efforts to limit carbon emissions. Be sure to watch the video that introduces this model and explains how to use the switches to change the FFB scenarios. To get the right answers, it is imperative that you have switches in the correct positions. If in doubt, try reloading the model (reloading the web page) and restoring all devices.

Before running the model, try to guess what will happen to global temperature change under the two reduced emissions scenarios — in one of them (the leveling off scenario), the emissions are held constant after 2010, and in the other (the halt scenario), they drop to zero after 2010.

1. Will the global temperature change level off by 2100 if the emissions level off?

  1. Yes
  2. No

2. Will the global temperature change drop to 0 by 2100 if the emissions drop to 0?

  1. Yes
  2. No

Now run all three emissions scenarios (keep the land use switch in the on position) in the following sequence: A2 (BAU), then FFB Leveling Off, followed by FFB Halt.

3. Focus on the second scenario — what happens to the global temperature change when the FFB emissions level off (leveling off begins in 2010)?

  1. Temperature does not level off — it just increases more slowly
  2. Temperature levels off right away
  3. Temperature levels off after 20 years

4. Now turn to the FFB Halt scenario — what happens to the global temperature change when the FFB emissions halt (the halt begins in 2010)?

  1. Temperature drops off right away and goes to 0
  2. Temperature drops off shortly after 2010 but does not return to 0
  3. Temperature levels off right away

5. QUESTION IN CANVAS SUBMISSION ONLY.

STEP 2. Please Note: The model in the videos below may look slightly different than the model (linked below) that you will use to complete Step 2. Both models, however, function the same.

Now we turn to a version of the model that has three emissions scenarios from the IPCC.

Video: Carbon Cycle (4:39)

Click here for a transcript of the carbon cycle video.

Hi, students, this is the model for step two, the second part of the lab, and I want you to familiarize yourself with this model before you get started. So basically, what we have here are three different switches down the bottom, that I'm going to explain, and we have the scenarios up here on the right side and the carbon cycle model, which is basically the same model as we used in the first part of the lab. So let me explain these switches. So what we have is the business as usual (BAU), which we talked about in the first step, A2, and this is the scenario here, A2 with fossil fuel burning, just keeps going up and up and up and up. And in the second one, we can turn this off. We have B1, which is our best case scenario, and turn that on. And then that is our drastic reduction of fossil fuel burning at around 2010, 2020, somewhere in there. Doesn't really matter when it is, but you can see it comes down significantly.

Ok, so that's the two, A2 with that switch on, B1 with that switch off and this switch on. And the third model, this is what's critical, is with both of these switches off, business as usual and B1. We have the A1B model, the basically likely, the likely scenario where fossil fuel burning starts to decrease in the later part of the century. Ok. It doesn't come down to zero, but it starts to decrease 2030, 2050, somewhere in there.

All right. So basically, those are our three scenarios. A2, B1, and A1B with both of these switches off. Ok. And finally, over here, we have a permafrost burning switch. This is going to this is going to show you what happens when we start burning permafrost and putting all that methane and CO2 into the atmosphere that is with this switch on. Ok, with this switch off, we do not introduce that methane and CO2 into the atmosphere. All right. So let me show you what happens. Basically, it's it's the same controls as we had in the... It's the same graphs we had in the last part of the lab.

All right. So let's run through them again really quickly. Let's do it with the A1B scenario. So we can run the A1B and you'll see temperature in 1, CO2 in 2, and again, if you run your cursor along here, it gives you a value in a year, calendar year, and a value, which you need to be able to do to to do well in this lab. pH comes down, and you can see that doesn't flatten out. And this shows you some of the same things we explained in the last lab. How much of the carbon is absorbed by the air. How much is absorbed by the ocean. How much is absorbed by terrestrial biosphere. This shows you fossil fuel burning in A1B.

This shows you permafrost, which we don't have on, obviously. This shows you how much is absorbed by the atmosphere, how much is absorbed by soil, how much is absorbed by land biota and we don't have permafrost on. This shows you surface in deep ocean. This shows you how much carbon we put in from fossil fuel burning. And this, again, shows you the comparison between the real data and read the observed data and the model that we ran here.

Ok, so let me just show you a couple more things before I set you free to work on this. So what we can do again is we can run different scenarios and compare them side by side so we can do that. This is A1B. Let's turn A2 on. So there's our A2 scenario, business as usual (BAU). Let's turn B1 on. And then that's our third one. That's our business, our B1 scenario, the best case scenario. Ok, and then finally, let me restore everything. Ok, let's run A1B. And now let me show you what happens when I turn permafrost burning on. And you can see a lot more fossil fuels, or a lot more carbon ends up into the atmosphere. And you can compare the curves side by side.

So I think you'll have a lot of fun with this. Make sure you understand these controls before you start. And please let me know if you have any questions.

Again, the A2 scenario is also known as “Business-as-Usual” in which we make no efforts to limit carbon emissions; the A1B scenario is one of modest reductions in emissions; the B1 scenario is one of more drastic reductions. Run all three emission scenarios (A2, A1B, and B1) with the permafrost switch off and the land use switch on, then answer the following questions.

Temperature (Page 1 of the graph pad)

  1. Which scenario produces the largest warming in 2100?
  2. Which scenario produces the smallest warming in 2100?
  3. What is the temperature difference between the highest and lowest emission scenario? (answer to 2.d.p)
  4. QUESTION IN CANVAS SUBMISSION ONLY.

    Atmospheric CO2 (pCO2 atm on Page 2 of the graph pad)
  5. Which emission scenario has the largest impact on drawing down CO2?
  6. When does that decrease begin?
  7. When does the rate of CO2 increase in A1B start to decrease?
  8. QUESTION IN CANVAS SUBMISSION ONLY.

    pH (Page 3 of the graph pad)

  9. pH is a measure of the acidity of the ocean — it is related to the amount of CO2 dissolved in the oceans. More CO2 in the oceans lowers the pH, which means the water is more acidic (a phenomenon known as Ocean Acidification). We will see in Module 7 that the key variable controlling the precipitation of reefs and other organisms that make shells of CaCO3 is a variable called saturation, which is indirectly related to the pH. Let’s assume for the next four questions that coral framework precipitation in a species of coral declines at a pH of 8.0 and that it can no longer form any below a pH of 7.8 (again this is hypothetical since saturation is key).

    List the emission scenarios that result in a slow-down in shell precipitation at any time during the model run (i.e., pH drops below 8.0).
  10. Which of the scenarios will stop the growth of coral reefs?
  11. What year does your answer from the previous question happen?
  12. QUESTION IN CANVAS SUBMISSION ONLY.

STEP 3.

Now, we will see what impact permafrost melting might have on the carbon cycle and climate. First, hit the “refresh” button on the browser to return the model to its original state. Run the A2 scenario with the PF switch in the off position, and then run it again with the PF switch turned on.

  1. How much additional warming is caused by 2100 in the A2 scenario by the permafrost melting?
  2. How much does the pCO2 atm increase by 2100 as a result of the permafrost melting?

    Hit the refresh button again, and then run the B1 scenario (the one with the more drastic reductions) with the PF switch off, then run it again with the PF switch on.
  3. How much additional warming is caused by 2100 in the B1 scenario by the permafrost melting?
  4. How much does the pCO2 atm increase by 2100 as a result of the permafrost melting?

This result might be a surprise to you, but remember how CO2 affects the climate — an increase of something like 100 ppm is much more important at lower concentrations than higher concentrations. So, going from 200 ppm to 300 ppm causes more warming than going from 700 ppm to 800 ppm.