In environmental science, a feedback loop is a process where indirect impacts either amplify or dampen the direct effects of an external stimulus. A change in the initial process affects the secondary process, which then has an impact on the initial process.

Positive feedback loops increase the impacts of the original stimulus. Negative feedback loops decrease its impacts: they are sometimes known as self-regulating systems. An example of a positive feedback loop is the role of water vapor as a greenhouse gas in earth’s atmosphere. Increasing levels of atmospheric carbon dioxide raise the temperature of earth’s atmosphere. This increasing temperature drives an increase in surface water evaporation, leading to more atmospheric water vapor. The increased water vapor acts as a greenhouse gas, further increasing the temperature of the atmosphere.

On the other hand, the increased reflectivity of clouds forms a negative climate feedback loop. Increased levels of carbon dioxide raise global atmospheric temperatures, which leads to the evaporation of water and the formation of clouds. However, clouds have a highly reflective surface, which helps to bounce excess solar energy back into space, thus cooling the atmosphere.

The amplifying effect of positive feedback loops in complex systems means that certain types of systems (like climate) are susceptible to tipping points. At a tipping point, a small increase in external stimulus can cause a stable system to transition into a very different state.