Climate Change Lesson 7 : Climate Models Making Global Predictions

1. How do scientists model the climate system?

Climate models are mathematical representations of the climate system. The climate system is often considered to consist of five main components:

• atmosphere

• hydrosphere (oceans, rivers, lakes)

• biosphere (global sum of living things)

• geosphere (rock, soil, and land surface)

• cryosphere (snow and ice cover)

Numerous physical, chemical and biological processes take place within and among the five main components.

Transparency 1: Modeling the Climate System is a graphic depiction of some of the elements which should be considered in trying to develop a climate model. The arrows show some of the relationships among factors. The relationships are important.

Identify some of the major relationships in the Modeling the Climate System transparency. Use Relationships in a Climate Model student activity for practice in interpreting a model.

Students complete the activity and share answers. (Note the layers in both atmosphere and oceans.)

2. Run a Very, Very, Simple Climate Model.

Demonstrate or have students go online to The Very, Very Simple Climate Model at http://www.windows2universe.org/earth/climate/cli_model.html. This model will calculate the amount of CO2 in the atmosphere and the average global temperature based on CO2 emissions.

To run the model:

• Decide how much CO2 will be released into the atmosphere each year and set the CO2 emissions rate.

• Then set the Timestep at 5 years.

• Click the Step Forward button to see how temperature and CO2 change.

• Continue to click to Step Forward button until you reach 2100.

• Record the starting and ending temperatures as well as the starting CO2 concentration.

• Refresh the screen after each model run and change the CO2 emissions for the next run.

Record the results of the model runs on The Very, Very Simple Climate Model student activity page. Run many scenarios with different carbon inputs to answer the questions: What trends do you see as you increase the amount of carbon dioxide emissions? (As the carbon dioxide emissions increase so does the temperature and the buildup of CO2.)

If we wanted to keep the carbon dioxide levels below 500 ppmv, how much carbon dioxide could be released? (Not more than 3 Gigatons of CO2 (GtC) per year.)

3. Developing Not So Simple Climate Models 

The Modeling the Climate System image is a diagram of some of the factors that influence climate in a single area. How do scientists develop models which look at all the relationships for every part of the world, and how the relationships change over time? How do they know their models are correct?

Show Evolution of Climate Models transparency.

Have students read and discuss How Climate Models are Developed and Tested (student resource).

Follow-up questions:

Why is the size of the grid cell important? (Large sizes generalize too much, but making the grid sizes smaller means many more calculations.)

What are some of the other difficulties of making a climate model? (Calculations of solar energy; number of layers of atmosphere and ocean; movement from cell to cell; changes in atmosphere.)

What are some potential sources of error? (The data could be wrong, our understanding of the relationships is, at best, incomplete, the formulas could be incorrect, and there could be programming mistakes.)

How do scientists test their models to see if they are correct? (By using data from the past to predict climate and climate changes.)

4. What did the IPCC Panel’s models predict?

The term climate projection is used by the IPCC when referring to model-derived estimates of future climate. When a projection is branded “most likely” it becomes a forecast or prediction.

A scenario is a coherent, internally consistent and plausible description of a possible future state of the world. It is not a forecast; rather, each scenario is one alternative image of how the future can unfold. The Intergovernmental Panel on Climate Change (IPCC) published a range of emissions scenarios known as the ‘SRES’ (Special Report on Emissions Scenarios). These various scenarios attempt to describe the different ways in which the world might develop in terms of population growth, economic growth, technological development and globalization. Each scenario is one alternative image of how the future can unfold. The scenarios are the socalled A1, A2, B1 and B2 storylines. Generally speaking, the ‘A’ scenarios describe a world in which economic growth prevails, while the ‘B’ scenarios describe a world in which concern for the environment limits economic growth somewhat. The ‘1’ storylines describe a world that becomes more globalized while in the ‘2’ storylines tend to preserve regional differences.

Computer Lab Option

Using the How Much and When? student activity, have students explore or demonstrate the SRES General Circulation Model (GCM) change fields website at http://www.ipcc-data.org/cgi-bin/ddcvis/gcmcf. They will be able to select a parameter (temperature, precipitation, etc.), type of model (high growth – A2, moderate growth – A1, and low growth-B1), month, and time frame to see a world map of what is projected to happen globally.

5. Tying it all together.

The Climate Scenarios transparency shows one of the major graphs from the IPPC report. The IPPC scenarios try to show data based projections of different futures, making a variety of assumptions about how human activity and how it may influence climate warming.

1. How much has the global land and ocean temperature changed in the last century? (About 1.3°F).

2. What was the projection for the temperature change by 2100? (It depends. There are several different scenarios for this ranging from 3.2 to 7.2°F. The average rate of warming over each inhabited continent is very likely to be at least twice as large as that experienced during the 20th century.)

3. Will every place on the Earth experience the same amount of change? (No, some areas will experience warming, some even cooling, but the overall global temperature is projected to increase.)