A feedback mechanism causes a change in a variable to keep changing in one direction or another. First, a variable needs to be picked. For example, surface temperature is a variable. Next, another variable is chosen to see how it impacts that first variable. For example, an increase in surface snow cover will cool temperatures since it reflects more radiation away. The cooler temperatures will in turn cause more snowfall. An increase in snowfall will cool temperatures more. This is a positive feedback mechanism since the relationship builds on itself over time.

A negative feedback mechanism acts in the opposite direction. For example, the addition of more moisture into the air will tend to warm temperatures since gaseous water is a greenhouse gas. However, the addition of moisture can also result in the addition of cloud cover. Cloud cover helps cool temperatures since it reflects sunlight and thus reduces the amount of sunlight that reaches the surface. The negative feedback mechanisms can prevent a runaway change in a variable from occurring. The negative feedbacks can be thought of as checks and balances that reduce or eliminate a positive feedback mechanism from continuing. Over time, equilibrium is achieved. This equilibrium is constantly being altered though by changes in various variables.