Here we introduce an application for a statistical model. The entire reason to generate such a model is to predict what future conditions might be (in a statistically averaged sense) given what we know about the situation being modeled.

The simulator that you can run can be run under many conditions to assess the sensitivity of global warming predictions to climate model parameters, population growth, and continued world economic development. YThe simulator has many different things to adjust and we can literally run hundreds of models with it (Beware the wicked witch ...). That is the entire point of statistics it allows one to generate scenarios in a scientifically defensible manner. Why we run screaming away from this instead of embracing this approach is beyond me and largely responsible for failed public policy at all levels.

Explanation of Simulation and Simulator Parameters:

We begin in the year 1900 with initial CO2 of 280 ppm, initial world population of 1.5 billion, and initial CH4 concentration of 20 ppm in equivalent CO2 units (we assume the global warming potential of one methane molecule to be 21 times that of one carbon dioxide molecule). This standard scenario will correctly reproduce the observations at the year 2000. From there we extrapolate to the future.

Our goal is to adjust various parameters, under various assumptions, to determine which models melt the world's polar caps and which don't.

Each time step of the model is 30 years and is activated by the "Take One Step Forward" button. You can read the data points off of any of the curve by mouseover on that curve.

Adjustable Parameters:

  • Pop = annual world population growth - the current real world value is about 1.1% (0.011)

  • Capacity = This is the carrying capacity of the Earth in units of billions or people. The default is set to 1000 - while completely unrealistic, this allows the business as usual exponential growth scenario to continue. For this exercise, don't change from the default value.

  • Coupling Factor = In this simulation, this factor is treated as a percentage of the total worlds population that uses Fossil Fuels. For the 20th century, an average of 1/6 of the worlds population using Fossil Fuels combined with an average population growth rate of 1.5% correctly yields both the world's population and the measured CO2 concentration in the year 2000.

  • Time Variance = This is the time, in years, it would take for the current fraction of the worlds population (set at 1/6 by default) to double its use of fossil fuels. For example, the default is +20 meaning that in 20 years 1/3 of the world's population will be using Fossil Fuels. If you set it to 40 years then it would take 40 years for 1/3 of the world's population. So carbon reduction intensities are coded into this. The bigger the number, the lower the carbon intensity. Note that operationally, we can shut off the CO2 channel by making the value for time variance to be negative

  • Anthro = This is the anthropogenic methane factor. In general it will remain at 1. However, if we can find ways to grow rice without producing methane, have co-energy generation at sewage treatment plants, eat less beef, etc, etc, you can set this factor less than 1. On the reverse side, the release of frozen methane and/or gas hydrates as a positive feedback mechanism (this is extensively discussed in Module 4). In this case, anthro will be greater than 1. In this simulation we have maxed it out at 3.

  • Lag = The time it will take for the atmosphere to initially respond in terms of having a temperature change with respect to CO2 buildup. Climatologists have no clue what this lag time might be. Empirical evidence suggests it could be as high as 75 years or as short as just 20 years - we just don't know. In any event, this is a free parameter which can be adjusted from 1 to 200 years. Obviously the longer it is, the more favorable the climate model will be.

  • Temp = This parameter controls the relation between CO2 increase and the raise in the average temperature of the Earth. We have no idea what this parameter is. A default value of 2 is used. Values less than 2 could be considered as favorable climate models while values greater than 2 are less favorable models which are more conducive for rapid and early melting of the polar caps. We will see that our melting times are quite sensitive to the choice of this parameter.

  • Polar = This is the temperature threshold which melts the polar caps. Obviously we have no idea what it is. The parameter can be varied from 2 to 8 degrees.

  • Melting = A green vertical line will appear when the Wicked Witch chimes in. This is the year at which the polar threshold was exceeded.

Here are some challenges and scenarios for you to do with this simulator

  1. Run the Business as Usual model but set pop growth to 0.009 (which represents some reasonable average from now until 2050). When do the polar caps melt? (put the cursor on the green line and read off the year) Does this scenario allow you to punt on any decision making?

  2. Now lower the time variance to 5 (this increases the rate of globalization) and take one step forward until polar caps melt. Are you worried yet?

  3. By now we have some methane feedback so set Anthro 2.5 and take on step forward until polar caps melt. Are you heading for the hills yet?

  4. New data suggests that the polar caps are far more fragile than we think and that climate sensitivity to increasing greenhouse gasses is higher than we thought it was in the year 2000. So raise coefficient to 3.4 and lower threshold to 3 to reflect these new data. No again, take one step forward until polar caps melt. (by now you probably turned your audio off). Whoops ....

  5. Challenge 1: Hit Rest to go back to default state. Change the population growth rate to .01 - your goal is to get out to the year 2300 before polar caps melt. You can change any of the other parameters you like. Is this possible?

  6. Challenge 2: Hit reset and then reset pop growth rate to .01 again. Sent Anthro to 2. Now try again to get to 2300 without melting - is it possible within the range of the adjustable parameters to do so? What are the implications of this?