Future Climate: Explore the Possibilities

Future Climate: Explore the Possibilities

Even simple models can help us understand how the rate of carbon dioxide emissions relates to climate change. The basic model below, called the Very, Very Simple Climate Model, gives us a peek into the future. You suggest the rate that you think humans will release CO2 into the atmosphere in the future and the model calculates what that means for atmospheric CO2 concentration and global temperature.

Models let you mix up scenarios for how things could be and see what happens if those scenarios were in place. Below are three scenarios. Test them out on the Very, Very Simple Climate Model and see for yourself what the future may hold.

 

Notes:

  • You can keep the Time Step Size the same (5 years). This will make it easier to visually compare results.
  • The Very, Very Simple Climate Model is undergoing revisions. An updated version will be available soon!

Scenario #1: What if the amount of carbon dioxide that we release into the atmosphere each year doesn’t change over time? The rate at which we are currently adding carbon dioxide to the atmosphere is the rate that we will emit CO2 in the future - around 9 gigatons of carbon per year (9 GtC/yr). To explore this scenario, use the controls along the left side of the model to do this:

  1. Set "Carbon Dioxide Emissions" to 9 GtC.
  2. Click the "Step Forward" button. You should see three points appear on the graph above the year 2020.
  3. Click the "Step Forward" button several more times, until you've filled out the graph to the year 2100. What do you notice in the graph?
  • Notice how the blue triangles (the emission rate of CO2 in GtC per year) make a horizontal line since the rate stays the same over time. Do you see the increase atmospheric concentration of CO2 (the black dots)? Adding CO2 at a steady rate causes the concentration to steadily climb. Red squares represent average global temperature in degree Celsius. In this model run, how much did the temperature rise by the year 2100?

Scenario #2: The glass is half full! People will rise to the challenge and limit the emissions of greenhouse gases in the atmosphere. Sure, it might take some time, but we will have new technologies and policies in place to limit the amount of carbon dioxide released. In this scenario, let’s assume that people will keep emitting carbon dioxide at an increasing rate until the middle of this century, and then we will have figured out how to stop polluting and the rate will fall.

  1. Click the “Start Over” button to clean the slate.
  2. As before, start with carbon emissions set at 9 GtC/yr.
  3. Click the "Step Forward" button twice to advance "model time" by 10 years to 2020.
  4. Increase emissions by 1 GtC/yr (to 10 GtC/yr) and advance another 10 years.
  5. Keep increasing the emission rate by 1 GtC/yr (to 11, then 12) for each time step and then advancing the model by 10 years using the "Step Forward" button.
  6. Once you reach the year 2050 (and an emission rate of 12 GtC/yr), start decreasing the emission rate by 1 GtC/yr for each decade (to 11, 10, 9, etc.).
  7. Run the model to the year 2100. What do you notice?
  • Did you notice that emissions (blue) increased until 2050, then steadily decreased through 2100? Did you see that CO2 concentration in the atmosphere (black) continued to rise even as emissions dropped? That’s because we were still pouring CO2 into the atmosphere, just at a slower rate. Temperature (red) follows a trend similar to that for CO2 concentration - continuing to rise even as emissions drop, but at a slower pace.

Scenario #3: Or perhaps the glass is half empty. What if people don’t invent ways to limit greenhouse gas emissions? What if people, instead, release more and more carbon dioxide into the atmosphere over time? This would mean that carbon emissions would rise steadily throughout the 21st century. What do you expect CO2 concentration and temperature to do?

  1. Also as before, start with carbon emissions set at 9 GtC/yr.
  2. Click the "Step Forward" button twice to advance "model time" by 10 years to 2020.
  3. Increase emissions by 1 GtC/yr (to 10 GtC/yr) and advance another 10 years.
  4. Keep increasing the emission rate by 1 GtC/yr (to 11, 12, ...) for each decade and then advancing the model by 10 years clicking the "Step Forward" button twice.
  5. Run the model to the year 2100. What do you notice?
  • Did you notice that emissions (blue) rose steadily in 2100? Atmospheric CO2 concentration (black) rose as well. When did they peak? How was temperature affected?

 

Some Notes About This Model

"All models are wrong, but some models are useful." - George E.P. Box

  • A major educational point embodied in this model is that temperatures depend on concentration, which rises whenever emissions are greater than zero. You've probably heard sound bites along the lines of "we are working hard to reduce the rate of growth of greenhouse gas emissions", presented as if such an approach would eventually lead to reduced temperatures.
  • This model is very, very simple. It knows nothing of changing wind or precipitation patterns that might accompany and in turn influence warming; it doesn't care where in the atmosphere the CO2 is; it ignores other greenhouse gases; and so on. In this simple model, the temperature is determined entirely by the atmospheric CO2 concentration via greenhouse warming of the atmosphere.
  • The assumptions behind this model, though rather limited, are valid as far as they go. The starting values for concentration, emission rate, and temperature are right around actual values for the year 2000. The ranges for emission rate choices are in line with predictions scientists think we are likely to see in the coming century. The relationship between atmospheric CO2 concentration and temperature uses a well-established relationship; basically, temperature rises about 3° C for each doubling of CO2 concentration. So, for example, if the concentration goes from 400 ppmv to 800 ppmv, we expect to see temperature go up by 3° C.
  • The Very, Very Simple Climate Model is available on the UCAR Center for Science Education website. It is free to use and requires no registration. This interactive was built using Flash, so you will need the Flash plugin from Adobe installed in your browser to view the interactive.
© 2011