Penn StateNASA

Simple Climate Model


We begin with a very simple analog model for our planet’s climate (figure below) in which solar energy enters the system, is absorbed (some will have been reflected), stored (some will have been transformed or put to work), and then released back into outer space. The amount of energy stored determines the temperature of the planet. The balance between the incoming energy and the outgoing energy determines whether the planet becomes cooler, warmer, or stays the same. Notice the little arrow connecting the box to the Energy Out flow — this means that the amount of energy released by the planet depends on how hot it is; when it is hotter, it releases, or emits, more energy and when it is cooler, it emits less energy. What this does is to drive this system to a state where the energy out matches the energy in — then, the temperature (energy stored) is constant. This energy balance sometimes called radiative equilibrium, is at the heart of all climate models.

Diagram showing the very simple concept of an energy flow system
Systems diagram for a simple energy flow system. Energy is added to a body (a reservoir in systems language), is stored by the body, and then leaves the body. The amount of energy stored determines the temperature, which in turn controls how much energy is released. This relationship between the energy out and the energy stored makes a negative feedback mechanism that tends to drive the system to a steady state where the energy in and the energy out are equal, and thus the temperature is constant.
Credit: David Bice