Carbon Cycle Lab
This lab uses a model of the carbon cycle to give you a sense for how carbon circulates
through the atmosphere, biosphere, oceans, and crust. It allows you to experiment with
how human input to the cycle might change global outcomes to the year 2100 and beyond.
One particularly relevant human impact is the increase in atmospheric CO2 levels. Between
the years 1850 and 2006, atmospheric concentrations have risen from 290 parts per
million (ppm) to over 380 ppm - a level higher than any known on Earth in more than 30
million years. Using the simulator, you will experiment with the human factors that
contribute to this rise and explore how different inputs to the carbon cycle might affect the
concentrations of the greenhouse gas CO2.
Part 1 - The Carbon Cycle
Step 1
Run the simulation to 2100 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 2050 and 2100. 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 1.5%. This rate of
increase is also a reasonable projection for the increase in global energy use, as the world's
economies continue to ramp up and populations grow.
1. If only one half of the plants in the world existed in 2100 (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. What happens to the level of atmospheric carbon as fossil fuel consumption
increases? Why does this happen?
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 plant populations?
What impact could twenty years at this level of consumption have on plant life?
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 animals? On marine plants?
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?
Conclusion
1. How will the increased carbon levels as noted in your Data Table affect current
animal and plant populations? Will the number and variety of species change? How
will they change?
2. From your collected data and what you have learned so far, what do you propose as
a solution to this dilemma?
3. Lesson 1:
4. Step 1
5.
To Year
Gaseous
Carbon
Atmosphere
Ocean Water
Ocean
Surface
Deep
Ocean
Fossil Fuels
Oil and
Gas
Coal
Biosphere Gaseous
Carbon
Soil
Terrestrial
Plants
2000
2050
2100
Lesson 1:
Step 2
To Year
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Total
Carbon
Emissions
Gaseous
Carbon
Smokestack
Atmosphere
Ocean Water
Ocean
Surface
Deep
Ocean
Fossil Fuels
Oil and
Gas
Coal
Biosphere Gaseous
Carbon
Soil
Terrestrial
Plants
Part 2 - 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 CO2emissions 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 pre-industrial levels.
Reducing carbon emissions to zero is far from realistic. Many scientists agree that a
doubling of the pre-industrial CO2concentration 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 CO2below 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 that percentage increased 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 50%. 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?
Conclusion
You've seen that the increase in fossil fuel use would have to be less than half of the
projected increase in energy demand (1.5% per year) in order to keep atmospheric
CO2 below 550 ppm. Consider what this means in real terms.
1. What non-carbon-burning energy sources could be used to keep carbon
emissions down?
2. Considering the extra carbon created by humans, how might it be possible
(or is it?) to generate more means of recycling carbon?
Lesson 2:
Step 1
To Year
Gaseous Carbon
Atmosphere
Ocean Water
Ocean Surface
Deep Ocean
Biosphere Gaseous Carbon
Soil
Terrestrial
Plants
2000
2050
2100
Lesson 2:
Step 2
To Year
2000
2050
2100
Gaseous Carbon
Net Def.
Rate
Fossil Fuel
% Increase
Atmosphere
Deep Ocean
Part 3 – The Feedback Effect
Part 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 2080, how has the terrestrial plant life population changed? What is the carbon
level in the soil and how does the carbon level affect the plant populations and
species variety?
2. Compare this chart to the first one you made.
1. In 2060, how are soil carbon levels different? In what ways will this
difference in soil carbon level show itself?
2. By 2060, 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?
Part 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 1/6 of the tundra will melt over 100 years. The
other predicts that 1/3 will melt over that same time period.
Assume that, in this hypothetical scenario, the tundra melting is inevitable and there is a
1.5% increase in fossil fuel consumption. Which of the two rates of melting would:
1. Have an impact on coastal seaweed populations in 2050? How great an impact?
2. Have an impact on atmospheric carbon in 2100 that is similar to another
scenario you’ve investigated? What similarities exist between these two
scenarios?
Conclusion
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 use and deforestation. If this increase in atmospheric CO2results in temperature
rises 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.
What are some viable ways of lessening the effect that increased carbon has on the
following?
1.
2.
3.
4.
Impact on human life
Destruction of the cycle
Global warming
Reduction or extinction of species, biomass
Lesson 3:
Step 1
Biosphere Gaseous Carbon
To Year
2000
2060
2080
2100
Net Def. Rate
Lesson 3:
Step 2
To Year
2000
2050
2100
Tundra
Melt
Rate
Net
Def.
Rate
1
Soil
Gaseous
Carbon
1
–—
-—
3
6
Atmosphere
Terrestrial Plants
Ocean Water
Ocean
Surface
Deep
Ocean
Fossil Fuels
Oil and
Gas
Coal
Biosphere Gaseous
Carbon
Soil
Terrestrial
Plants