Selecting Appropriate Models in Science

Instructor: Marc Chiacchio

Marc has taught Bachelor level students climate science and has a PhD in climate science.

Scientific models are used to describe physical phenomenon and are tested against real world data. In this lesson, you will become familiar with a real example of how scientists select appropriate models for their work including knowledge of their limitations.

Scientific Models

Have you ever seen computer simulations of a star exploding or planets with habitable life on TV? These are visual models that are used to teach us about how certain events in nature work. In this example, these simulations are also computer models, which use current knowledge to simulate future events using mathematical computer code. Climate models that simulate the future climate of Earth or even the far past is another example of a computer model.

Scientific models can also exist as diagrams showing the circulation of the atmosphere, or as an actual physical model, such as the solar system that a teacher might use in a classroom. Scientists in the lab use these same types of models to explain complex concepts in simpler terms to other colleagues.

Example of the Earth
atmosphere

The main function of a scientific model is to convey a basic idea that may be less understood, and then try to explain it more clearly with a known physical mechanism or process. A scientific model must also be able to predict future events. They are tested with real data, and once they are capable of producing reliable results, the predictions are accepted by the scientific community.

Alternative Models

The debate about whether humans have been affecting the climate comes to light in the public mainly because scientists have been using more than one climate model. By using alternative models and taking into account many aspects of the climate, scientists are able to inspect whether a certain phenomenon they are testing is reliable enough to make predictions.

Once a particular model has failed to explain a physical concept, that model is discarded and the alternative model that better fits the phenomenon is kept. Also, many times the mechanisms that are tested in these discarded models are incorporated into the new model in order to improve the computer simulation.

We will see in the next section an example of how this works with climate models and how scientists select more appropriate models for their research.

Climate Models

Scientists have proposed many mechanisms that contribute to changes in the climate. Natural changes have been proposed, like solar activity or volcanic eruptions, as well as human-induced changes like increasing concentrations of carbon dioxide contained in the atmosphere. Carbon dioxide in this context is produced by fossil fuel emissions and can trap heat in our atmosphere, thereby raising surface temperatures.

Scientists can test these possibilities. By allowing for a particular model to see how well solar activity influences this rise in temperature, this aspect of the model is turned on and the rest is turned off such as human-produced carbon dioxide. This is accomplished in the computer code itself.

The results from this experiment are then compared against the actual rise in temperature that we see from real data. In the next experiment, the solar activity is turned off and the carbon dioxide is turned on. The results are once again compared against real data.

The global temperature time series from data.
temp

In order to properly compare these two experiments, statistical tests need to be applied such as a simple correlation. The correlation is a quantity that measures the interdependence of two variables. You can also see by visual inspection how well the two experiments compare to the real data.

In this example, the models that incorporate human-induced climate change such as carbon dioxide are more successful at explaining the recent rise in the Earth's temperature. This is just one example of how scientist select the most appropriate model in science.

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