Credit: UCAR/NCAR

This time-lapse video shows 42 time steps in a hands-on activity that illustrates how models of Earth's atmosphere and climate work.

The What is a "model"? activity was created by the Little Shop of Physics at Colorado State University.

In the activity, students move red markers - which represent sunlight, heat, and longwave infrared radiation - between three game boards representing Earth's surface and the lower and upper parts of Earth's atmosphere. The "rules" of the model tell students how many of the red markers to move, and where, each turn. As the model runs, it illustrates how heat flows throughout the Earth system. The model illustrates how the greenhouse effect warms Earth's surface and how Earth's atmosphere is cooler at higher altitudes.

In this video, the model is started (at Time = 0) with a somewhat arbitrary set of initial conditions. At the start, the temperature (as indicated by the number of red markers) of Earth's surface (far left game board) is 19 degrees. At the start, the temperature of the lower atmosphere (middle game board) is also set at 19 degrees, while the temperature of the upper atmosphere (right board) is set at 8 degrees.

As the model runs, the three temperatures (Earth's surface, lower atmosphere, upper atmosphere) gradually adjust themselves based on the "rules" of the model.

In this model run, the Sun is "on" during the first three time steps, followed by three turns of nighttime. Day and night, each lasting three time steps, alternate for the rest of this model run. During each day turn, three red markers, representing sunlight, flow into the board representing Earth's surface. During the nighttime turns when the Sun is down, the incoming "flow" of sunlight to Earth stops, and no red markers from the Sun are added to the board representing Earth's surface.

The model gradually "spins up" from the arbitrary initial state, eventually settling into a repeating pattern of temperatures in each of the regions represented in this model - Earth's surface, the lower atmosphere, and the upper atmosphere. This repeating pattern of temperatures throughout the day/night cycles is called a dynamic equilibrium state.

If the Sun is left "on" all the time, the model eventually reaches an unchanging state with fixed temperatures in each of the three regions. That state is referred to as a "static equilibrium". Since this model run includes the varying input of sunlight caused by the day/night cycle, it does not settle into fixed temperatures in a static equilibrium state. Instead, it settles into a dynamic equilibrium state with a repeating pattern of rising and falling temperatures through each day/night cycle. This model run reaches the repeating, dynamic equilibrium state by time step #28.

The graph below shows the changes in temperature of Earth's surface, the lower atmosphere, and the upper atmosphere over the course of this model run.

A version of this time-lapse video that runs twice as fast is also available. Some patterns are more readily apparent in the speeded-up version. Also, a looping video showing the repeating pattern of dynamic equilibrium that this model run eventually "spins up" to is also available.