STELLA Modeling as a Tool for Understanding the Dynamics of Earth Systems

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STELLA Modeling as a Tool for Understanding the
Dynamics of Earth Systems

• Dave Bice
• Dept. of Geology
• Carleton College
• Northfield, MN
• Dbice_at_carleton.edu

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Outline

• Overview of the Modeling Process
• Simplicity vs. Complexity in Model Design
• Getting Acquainted with System Behaviors
• Example of the Global Carbon Cycle
• Educational Benefits of Modeling

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The Modeling Process

• Develop Conceptual Model Reservoirs, Processes,
  Relationships
• Simplify
• Find Data for Reservoir Initial Values, Fluxes
• Convert Conceptual Model to STELLA Diagram
• Mathematical Representation (Parameterization) of
  Processes
• Initial Testing of Model Establishment of
  Steady State or Alternative Control
• Test Model Against Observational Data (when
  possible)
• Experimentation Question Asking
• Interpretation of Results, Generation of More
  Questions, Further Experiments

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From conceptual model to STELLA model
Simplicity vs. Complexity
Conceptual model for 3
Increasing simplicity
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Increasing connections and complexity
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Common System Behaviors I
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Common System Behaviors II
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Common System Behaviors III
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Common System Behaviors IV
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Common System Behaviors V
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The Global Carbon Cycle
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STELLA Diagram of Global C Cycle
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Parameterization of Soil Respiration
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Parameterization of Photosynthetic Uptake of
Carbon
Fp is the global rate of photosynthetic uptake of
CO2 in GtC/yr. Pmax is a parameter with units of
GtC/yr that is used to force the equation for Fp
to give the proper value corresponding to the
starting conditions of the model. Khs 62.5 ppm
the half-saturation value the atmospheric CO2
concentration at which the rate of
photosynthesis, Fp, is half of the ultimate
saturation value, given that particular
temperature pCO2atm,init 280 ppm the
pre-industrial atmospheric CO2 concentration pCO2a
tm,min 30 ppm value below which no
photosynthesis can occur pCO2eff pCO2atm -
pCO2atm,min the effective atmospheric CO2
concentration Fp,init 100 GtC/yr the initial
value for global photosynthesis Tsensp 0.04
establishes the increase of Fp per degree of
warming ?T T - Tinit temp. difference
relative to initial temp., Tinit is set to 0
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Ocean Carbonate Chemistry Scheme
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Testing the Model
Year Fossil Fuel Land-Use
Gt C/yr GtC/yr 0
0.350 0.6 10
0.525 0.6 20
0.805 0.65 30
0.959 0.65 40
1.078 0.7 50
1.300 0.7 60
1.638 0.8 70
2.586 1.1 80
4.084 1.3 90
5.292 1.25 100
6.098 1.5
Observed Increase in Atmos. CO2
Units are Gt C for Soil and Land Biota ppm for
CO2
The model results closely match the observed
record for the same time period. This means that
the carbon cycle model generates meaningful
results so long as there is not some kind of
non-linear mode switch that becomes important in
the future.
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Experiment Looking into the Future
In these experiments, we start off with the
emissions history of the last 100 years and then
project different emissions scenarios into the
next 100 years. a) Business-as-Usual
Projecting the curve of fossil fuel emissions
using the most recent slope b) Stabilization
Emissions steady at current flux for the next 100
years c) Reduction Emissions drop to zero
next year (dream on!)
Business-as-usual
Atmos CO2
Stabilization
Reduction
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Where did all the carbon go?
Atmosphere
Stabilization scenario
Deep Ocean
Land Biota
Surface Ocean
Soil
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Looking Farther into the Future
Stabilization scenario
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Benefits of Modeling with STELLA

• Simple Graphical Interface, No Programming Skills
  Needed (can be used at an introductory level)
• Model Construction Motivates Learning About
  Relevant Processes
• Adds a Quantitative Dimension to the Learning
  Process
• Allows for Experiential Learning
• Watching the Dynamics Unfold Develops an
  Understanding of Dynamics
• Leads to Development of Systems Thinking