The Habitable Planet Carbon Lab - Claremont AP Environmental

The Habitable Planet: Carbon Lab

Name: __________________________

Date: ___/___/___

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The Carbon Cycle

Step 1

Run the simulation to 2110 with the default settings, and, using your Data Table, record the total carbon levels in each "sink" (terrestrial plants, soil, oil and gas, coal, surface ocean, and deep ocean) at 2060 and 2110. Using the data you collect from the model, answer the following questions while thinking about how the model mimics real-life conditions.

Note: The default setting for the increase in fossil fuel use per year is 2.5%. This rate of increase has been our recent experience for the increase in global energy use, as the world's economies ramp up and populations grow.

1. If only one half of the flora in the world existed in 2110 (perhaps due to deforestation), what do you predict the atmospheric carbon level would be? How would you change the simulation to reflect this?

2. What is the relationship between increased carbon in the ocean and increased carbon in the soil? How else might carbon be transferred to soil?

3. Using the data generated by the simulation, determine the mathematical relationship between the percentage increase in fossil fuel consumption and the increase in atmospheric carbon. Is the relationship linear?

Step 2

In many scenarios, the atmospheric concentration of CO2 is projected to increase beyond 700 ppm by the end of the century. However, this increase in atmospheric carbon doesn't account for all of the carbon released by burning fossil fuels.

To find out where all the carbon really goes, run the simulation again, one decade at a time. Record the total amount of carbon in the atmosphere (the number in the sky) and other carbon sinks (terrestrial plants, soil, surface ocean, and deep ocean), as carbon moves through the system. Note that 1 ppm of atmospheric CO2 is equivalent to 2.1 GT (Gigatons) of carbon. As you record your data, keep in mind that this is a simulation of real life. Think about the questions below.

1. What is the relationship between an increase in fossil fuel consumption and increased carbon in terrestrial plants? How might this change flora populations? What impact could twenty years at this level of consumption have on flora?

2. What is the relationship between an increase in total carbon concentration (the smokestack) and increased carbon in the ocean surface? How might this change marine life populations? What impact could fifty years at this level of emissions have on marine fauna? On marine flora?

3. In addition to circulating through the carbon cycle, where else might excess carbon be found? In fifty years, where would you be most likely to see excess carbon?

4. Which areas are most highly (and quickly) affected by an increase in carbon emissions (and increase in fossil fuel consumption)? How would these effects manifest themselves? What are the dangers/benefits to these areas?

For Your Consideration

You should now have some understanding of how carbon moves through the system, but you may be wondering about

the mechanisms behind this flow. As you read through the following explanations, refer to your Data Table for Lesson 1 Step 2.

Atmosphere: combustion of carbon-based fuel combines carbon, C, and oxygen, O2, adding CO2 to the atmosphere. CO2 is not a by-product of fossil fuel use; it's the direct product of the very reaction that releases the energy.

Biosphere (Terrestrial Plants and Soil): plants (biomass) inhale CO2 and exhale O2. When there's more CO2 available, biomass tends to breathe in more, and therefore grow more. Most scientists now believe that plants have a limited ability to increase their growth rate.

Surface ocean: The amount of gas dissolved in any liquid is proportional to the partial pressure of that gas in the vapor phase above the liquid (Henry's Law). As a result, if we increase the partial pressure of atmospheric CO2 (i.e. increase the concentration of CO2), then we force more CO2 gas to dissolve into the liquid. (In this case, the liquid is the ocean.) In addition to the CO2 dissolving into the liquid as a gas, CO2 reacts with H2O and forms bicarbonate ions (HCO3-) and carbonate ions (CO3--). This combustion of fossil fuels results in an increase in dissolved surface ocean carbon and a decrease in pH.

Deep ocean: Ocean chemistry involving mineral precipitation, and biological activity, and ocean currents transport the carbon from the surface ocean to the deep ocean over long time-scales.

Thinking Ahead

1. How will the increase in biosphere production of carbon alter the carbon levels in: 1. Atmosphere 2. Surface ocean 3. Deep ocean 4. Fossil fuels 5. Number and variety of terrestrial plants and animals?

2. How will the increased carbon levels as noted in your Data Table affect current taxonomy? Will the number and variety of species change? How will they change?

3. From your collected data and what you have learned so far, what do you propose as a solution to this dilemma?

Curb Emissions

Step 1

In a best-case (but very unrealistic) scenario, imagine that scientists suddenly discovered an unlimited, clean, and cheap fuel source that emitted no CO2 into the atmosphere, thus bringing fossil fuel use down to zero. What would happen? Would the carbon cycle naturally bring atmospheric CO2 levels back to pre-industrial levels (below 280 ppm)?

Press the "NONE" button next to fossil fuel use to bring CO2 emissions to zero in the simulation. Then run the simulation for a hundred or more years to see what happens. Record your data and compare it to your previous entries. Answer the questions below.

1. How have atmospheric carbon levels changed? 2. Without any fossil fuel consumption, which parts of the cycle have improved their carbon levels in comparison to previous

data? Which sections of the cycle have improved from the previous levels you have recorded but still are increasing their carbon levels?

Step 2

As you saw in Step 1, even with no further input from humans, the elevated levels of atmospheric CO2 caused by a century of fossil fuel burning will continue to impact the carbon cycle because the system attempts to reach a state of equilibrium, with the exception of the gradual moving of carbon from the surface to the deep ocean, which happens only over longer time-scales. It could take 2000 years or more for this process to restore atmospheric CO2 to preindustrial levels.

Reducing carbon emissions to zero is far from realistic. Many scientists agree that a doubling of the pre-industrial CO2 concentration to approximately 550 ppm is a reasonable target to shoot for in order to avoid the most serious impacts on climate and ecosystems. How much of a change in fossil fuel consumption would we have to make to limit atmospheric CO2 to that level?

Return to the simulation and change the annual percentage increase in fossil fuel usage until you can keep atmospheric CO2 below 550 ppm in 2100. Once you have found an appropriate level of fossil fuel percentage increase, predict what would happen if fuel use stayed at the that percentage increase and deforestation decreased. In fifty years, if deforestation were decreased 50%, how would the carbon levels in the soil change? Run the simulation to test your hypothesis. Were you correct? Were you surprised by the result? What about your result surprised you?

1. What effect does a high carbon level have on the deep ocean? Why might it be important to keep an eye on the deep ocean carbon levels? What could that one number tell you about the cycle as a whole?

2. Try reducing the level of fossil fuel percentage increase and decrease deforestation by 1 GT per year. Predict what will happen to the atmospheric carbon levels and record it in your Data Table. Run the simulation to test your hypothesis. Were you correct? Were you surprised by the result? What about your result surprised you?

For Your Consideration

You've seen that the rate of increase in fossil fuel use would have to stop in order to keep atmospheric CO2 below 550 ppm, despite a projected increase in energy demand (currently 2% per year, though it rose to 2.5% during 2000-2010). Consider what this means in real terms. What non-carbon-burning energy sources could make up the difference? And how fast would their adoption have to increase? You will explore this question in the Energy lab.

Thinking Ahead Considering the extra carbon created by humans, how might it be possible (or is it?) to generate more means of recycling carbon?

Feedback Effects

Step 1

So far we have considered only the impact of burning fossil fuels. But there are other human activities that influence the carbon cycle. One major factor is deforestation and land use. Currently, land use (for example, rice paddies) and deforestation outstrip reforestation by roughly 1 GT per year. If deforestation were to increase, perhaps due to increased burning of rainforests, carbon would be transferred first from terrestrial plants to the atmosphere and then through the rest of the carbon cycle as seen in Lesson 1.

Change the net deforestation rate and observe how that impacts the carbon cycle. Note that deforestation is expressed as GT of carbon released, not as a percentage rate of increase. Realistic deforestation estimates would remain less than

2 GT per year. Record what happens to the system at a steady net deforestation rate of 1.6 GT per year and answer the following:

1. By 2090, how has the terrestrial flora population changed? What is the carbon level in the soil and how does the carbon level affect the flora populations and species variety?

2. Compare this chart to the first one you made. 1. In 2070, how are soil carbon levels different? In what ways will this difference in soil carbon level manifest itself? 2. By 2070, how might the worldwide decomposer populations change? What effects could `business as usual' and the last rate of deforestation you selected have on human health?

Step 2

There are several important natural systems that may be affected by greenhouse warming as atmospheric CO2 rises. Some of these systems may release even more CO2 into the atmosphere, speed up the warming, and cause a positive feedback loop. Which feedback effects will actually take place is hard to predict in such a complex system, but a model for one feedback effect is included in the simulator: melting tundra. If the arctic tundra were to melt as temperatures rise, its stored carbon would enter the system. You will find two possible scenarios. One model assumes that 1/12 of the tundra will melt over 100 years. The other predicts that 1/6 will melt over that same time period.

Assume that, in this hypothetical scenario, the tundra melting is inevitable and there is a 2% increase in fossil fuel consumption. Which of the two rates of melting would:

1. Have an impact on coastal seaweed populations in 2060? How great an impact? 2. Have an impact on atmospheric carbon in 2110 that is similar to another scenario you've investigated? What

commonalities exist between these two scenarios?

For Your Consideration

As you have seen in this lab, despite the natural tendency of the carbon cycle to regulate the amount of carbon in the atmosphere, the system is currently being overwhelmed by human fossil fuel combustion and deforestation. If this increase in atmospheric CO2 results in temperature rise as scientists predict, there are several possible factors that could cause feedback effects. If human beings are to mitigate these risks, they will have to take strong action soon.

In the Energy lab, you will explore the nature of some of the changes we could make in our global energy use and how these changes could affect our planet's delicate balance.

Thinking Ahead What are some viable ways of lessening the effect that increased carbon has on the following?

1. Impact on human life 2. Destruction of the cycle 3. Global warming 4. Alteration/destruction of species, biomass

The carbon cycle is only one of many natural (and human "enhanced") cycles: hydrogen, water, nitrogen, and oxygen are some other cycles you may want to investigate. Think about how these cycles have changed due to human impact.

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