GLY 1073 - Carbon Cycle Model

The purpose of today's exercise is to construct a simple carbon cycle model using Stella.  Next week, we will couple this model to the population model to predict future changes in atmospheric pCO₂.

1.) We will begin by building a model before man began to affect carbon flow.  Construct a five reservoir model using the diagram below.  For the pre-anthropogenic model, do not include the fossil fuel or deforestation fluxes or missing sink.  Set the atmospheric reservoir to 600 Gt (not 720) to reflect the pre-Industrial concentration of CO₂ in the atmosphere.  Set both the Oceanic Uptake and Oceanic Release to 105 Gt/hr.  Run the model for 100 years. 

a.) What happens to the size of the atmosphere, land plants, soils, geosphere, and ocean reservoirs?  Why? 

b.) If 1Gt of carbon is equivalent to 0.47 ppm atmospheric CO₂, what was the pre-industrial atmospheric CO₂

2.) Next add the anthropogenic fluxes and missing sink.  Where is the missing sink? These flux estimates are "1990" estimates.  Set the atmospheric reservoir to 720 gT (corresponding to 338 ppm).  Set the Oceanic Uptake to 107 Gt/yr.  Run the model for 110 years (to 2100) assuming constant 1990 rates of deforestation and fossil fuel combustion. 

a.) What happens to the the size of atmosphere, land plants, soils, geosphere, and ocean reservoirs?  Why? 

b.) What will the atmospheric CO₂ concentration be in 2100 assuming these 1990 rates?  What is the percentage increase relative to the pre-Industrial concentration? 

c.) How valid is the assumption of constant rates of anthropogenic emissions?  Are emissions rates likely to increase or decrease for the next 50 years? 

Note:

All reservoirs of carbon are in units of 10¹⁵grams of carbon (10¹⁵grams of carbon = One Pg [petagram]= one gigaton (Gt) = one billion metric tons = 1000 x one billion kg ).

All fluxes are in 10¹⁵grams of carbon per year.

Values given are "1990" estimates.