FeedbackLoops
One way in which components of Earth’s climate system interact is through feedback loops.
Feedback loops consist of connections from a component that circle through one or more
components back to influence the original component. Before climate change, balancing feedback
loops kept Earth’s climate in equilibrium. However, the balance has been changed by the increase of
greenhouse gases in the atmosphere. This is significantly changing how the climate system works.
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This short, fun video from NASA gives a clear explanation of the albedo effect, and how it
can cause a reinforcing warming feedback loop (3:46)
https://www.youtube.com/watch?v=cW4JTHz1aRg
Feedbacks can be either “reinforcing” feedbacks or “balancing” feedbacks. Balancing feedbacks
dampen or suppress an effect, as shown in this diagram:
Balancing feedback: Human energy use increases greenhouse gases. This causes a rise in
temperature. The negative environmental impacts that result cause human concern. This
results in attempts to reduce energy use.
Reinforcing feedbacks strengthen or amplify an effect, as shown in the next diagram:
Reinforcing feedback: Human emissions cause a rise in greenhouse gases. This results in
rising temperatures. Hotter conditions increase human discomfort. As a result, humans
increase their use of air-conditioning. Increased AC use increases emissions.
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Another example of a reinforcing feedback is the melting of land and sea ice at the poles. Because
ice is light-colored, a large proportion of the sunlight that hits it bounces back to space. We say that
ice has a high “albedo” since it reflects a high proportion of the solar energy. Since a lot of the
incoming energy is reflected, this high albedo limits the amount of solar energy that is absorbed by
the ice.
As the world gets warmer, the ice melts, which reveals land or water below. These have a darker
color than ice. The darker color means that less heat energy is reflected – land and water have lower
albedo. This, of course, means that more of the sun's energy is absorbed. This leads to more
warming, which leads to more ice melting – a reinforcing feedback.
A reinforcing feedback from melting ice cover. Source: PBS
Another important reinforcing feedback due to global warming is caused by molecules of water
vapor in the atmosphere.
A reinforcing feedback from water vapor. Greater evaporation of water from land due to
higher temperatures adds to water in the atmosphere. Water vapor is a greenhouse gas that
absorbs solar energy, contributing to higher temperatures. Source: SERC
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Water vapor is in fact the most abundant greenhouse gas! Warmer air can hold higher amounts of
water vapor than colder air can. More water vapor in the air acts as a greenhouse gas, which causes
more heat energy to be absorbed. This leads to even higher temperatures. This is shown in the
diagram above.
More information:
• How reinforcing climate feedbacks work (5:00) (Here called “amplifying” feedbacks)
http://on.aol.com/video/how-climate-feedbacks-worsen-global-warming-516923291
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