Penn State NASA

Lab 5: Carbon Cycle Modeling


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.

This is the interface to the carbon cycle model that we will be working with in this module. If we click on this button here, we would see a view of what the carbon cycle looks like that's implemented in this model. It's a complicated thing, but it's a very realistic carbon cycle model that's going to allow us to explore, in a pretty realistic way, what will happen to atmospheric CO2 and to other aspects of the carbon cycle as we change the burning of fossil fuels and the human effect on this particular system. This carbon cycle model here is attached to a little climate model, that you can see the edge of it over here, that's the same one that we worked with in Module 3. And so, the carbon cycle model will control the atmospheric CO2 concentration here, and then, that will feed into the climate model here and control the greenhouse effect. And then, the temperature, determined by the climate model, will then come back and affect different parts of the carbon cycle model here.

So, let me show you how to work this this model. If you run it just the way you first open it, you'll see it calculates the global temperature change over time. So, zero is the temperature at 1880, but this is temperature relative to that time. And then, the temperature rises as we go to the year 2000 and 2100. Now, these switches down in here control different histories or scenarios of fossil fuel burnings. The business-as-usual emission scenario is what we ran first. So. when this switch is on, it uses that business-as-usual scenario and it looks like this, where the carbon emissions just go up and up and up with no change all the way to 2100.

If we click this off, and leave this switch off, it's going to implement a scenario in which the fossil fuel burning just levels off. So, after the year 2010, it just levels off like this. So, we hold emissions constant, and we can see what happens to the temperature in the rest of the system in that case. If we turn this switch on, like that, it will implement this scenario here. It's a very unrealistic one, where after 2010 we drop quickly down to zero fossil fuel burning for the rest of time. So, this is a really dramatic case, just to see how the system will respond to that change.

Now, you can graph different parts of the system. Here, we can look at the atmospheric CO2 concentration. Here, we can look at the ocean pH. Here, we can look at where the carbon goes, what fraction of it stays in the atmosphere, what fraction goes into the biosphere, and what fraction goes into the oceans. This shows us the details of the fossil fuel burning history that we applied in that case. This plots both the atmospheric CO2 concentration and the fossil fuel burning history together, so you can see how they compare. This shows the values of carbon and all the different reservoirs in the carbon cycle model. This is the cumulative amount of carbon that we've released over time, so it just gets bigger and bigger and bigger. This is not the annual amount, but the cumulative.

Now, this is an interesting one to look at because it goes from 1880 to 2010, so the period of time that we know something about. And it plots in red the actual observed atmospheric CO2 level and in blue the CO2 level that the model calculates. And so, you can see that those two are very close throughout this whole time. And so, that means that that our carbon cycle model, coupled with the climate model, is giving us a result that matches a historical record. And so, we say we have a good model, and we can essentially trust what it tells us in terms of projections off into the future.

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


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.

This is the interface to the carbon cycle model that you'll be working with in this module. If you click on this button here, it gives you a diagram of the carbon cycle. It's a complicated looking thing down here, but all these boxes are just places where carbon can reside, including the atmosphere here. And the amount of carbon in the atmosphere determines the CO2 concentration in the atmosphere, which then affects other parts of this.

Let me point out a couple of things about this diagram. One is that there's a fossil fuels reservoir here, that includes a flow called fossil fuel-burning, ffb, that adds carbon to the atmosphere. And this is controlled by different kinds of emissions scenarios that would dictate the amount of carbon released at each year, through this process of burning fossil fuels. It also includes a reservoir for permafrost carbon, so that’s carbon stored in permafrost. But if the permafrost melts, then that will be added to the atmosphere here. And that's controlled by a switch that we can either turn on or off to consider the effect of that. The CO2 concentration in this carbon cycle model then feeds into a climate model that you can see the edge of it over here. It's the same climate model that we worked with before. So, there's a connection between these two. And then, this determines the global temperature change that then, in turn, affects the carbon cycle. So, these two are linked very closely to each other.

Now, let's see how you operate this. This carbon cycle model will allow you to impose three different emissions scenarios on it. One is the business-as-usual scenario. If you click on this, you see what that scenario is, just an increasing emission of carbon over time. It begins in 1880 and then ends in 2100, so it goes into the future a bit. Here's another emission scenario, one that involves moderate reductions after some period of time here. And then, finally, there's a third emission scenario here that's shown like this, more drastic reductions through time.

So, you can activate those three different scenarios by using these two switches here. So, the way it comes right now, it will impose the business-as-usual (BAU) scenario, that's A2 here. So, if I run it, it's gonna impose that emissions scenario on from 1880 up to 2100. And you see the temperature change, and you can see the CO2 concentration atmosphere rising up here to very alarming levels. You click again, it shows the pH and the oceans going down, down, down, getting more acidic. And it shows how much of the carbon stays in the atmosphere and the airborne fraction, how much goes into the oceans, and how much goes into the terrestrial reservoirs. Click again, it shows a history of fossil fuel-burning and detail from that emission scenario. And then, through here, this shows the permafrost melting. That's turned off now, so that didn't do anything. And then, this graph and the next one show just the amount of carbon, in terms of gigatons, in those different reservoirs over time. And this shows the total anthropogenic change, which is the cumulative effect of burning fossil fuels and having land-use changes.

So, if we wanted to impose a different scenario, we would turn this switch off. And now, we're looking at one of these reduction scenarios. So, if I have this switch down like that, it's going to implement the aA1B scenario, and if I click this, there it goes. And then, if I click the switch, it's going to impose the B1 scenario here. So, if I run it, you'll see that take effect. All right, so that's how you activate those different scenarios. If I want to turn on the permafrost melting, I would hit this switch here. Now, as the temperature rises up above a certain level, once it gets above 1 degree, then the permafrost melting begins. So, I'm going to turn that off here. And this switch here determines whether or not the carbon emissions from land-use changes, including forest burning and soil disruption, is either not turned on, or turned on in this case, that's the standard scenario. So, that's the essence of how this carbon cycle model works.

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)

    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?

    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?


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.