Assignment: Scientific Measurements



The Carbon Cycle

[pic]

Name of Student:       Date:      

Go to the Interactive Lab site:

This model is similar to ones presented by the Intergovernmental Panel on Climate Change. 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.

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.

Step 1: Carbon Cycle

To find out where all the carbon really goes, run the simulation, 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.

The simulator is already set to default for this simulation. Simply hit “Run Decade” and record your data with each click.

|Step 1 |Total Carbon |Gaseous Carbon |Ocean Water |Fossil Fuels |Biosphere Gaseous Carbon |

| |Emissions | | | | |

|To Year |Smokestack |Atmosphere |Ocean Surface |

|To Year |Atmosphere |Ocean Surface |Deep Ocean |Soil |Terrestrial Plants |

|2000 |      |      |      |      |      |

|2050 |      |      |      |      |      |

|2100 |      |      |      |      |      |

Answer the following questions:

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?      

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

As you saw in Step 2, 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 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.

Step 3: Feedback Effects

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.

Change the lesson to Feedback Effects. Change the net deforestation rate and observe how that impacts the carbon cycle. You can do this by clicking and dragging the green block on the Net Deforestation Rate or by typing in a value. 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 (so use a value less than 2). Record what happens to the system at a steady net deforestation rate of 1.6 GT per year.

| | |Biosphere Gaseous Carbon |

|Step 3 | | |

|To Year |Net Def. Rate |Soil |Terrestrial Plants |

|2000 |enter your # |      |      |

|2060 |enter the same # |      |      |

|2080 |enter the same # |      |      |

|2100 |enter the same # |      |      |

Answer the following questions:

1. By 2080, how has the terrestrial flora population changed?      

2. What is the carbon level in the soil and how does the carbon level affect the flora populations and species variety?      

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.

1. What effect on atmospheric carbon levels would you expect to see as a result of this tundra melt?      

Run the simulation by clicking the 1/3 or 1/6 option next to the Melting Tundra option and verify your decision.

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 order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download