Initial Publication Date: July 7, 2011

Carbon on the Move!

Part C: Carbon Cycle Feedbacks

When you took your carbon journey through the carbon cycle in Lab 2B, you moved through a complex system of carbon processes and reservoirs with many changes along the way. Understanding the carbon cycle and how it behaves requires that we think of it as a complex dynamic system with components of the system interacting with each other in often unpredictable and emergent ways. A change in one part of a complex system can often cause a myriad of changes in other parts of the system. The Amazon forest ecosystem is a good example of a complex ecosystem currently undergoing changes.

Discuss

Examine the image of the Amazon Rainforest Die-off pictured above right. Discuss and share your thoughts with a group and/or the class.

Identify as many environmental variables in this story as you can. HINT: Two examples would be trees and CO₂.
What do you think the arrows mean in this diagram?
What causal connectionscause and effect relationships between parts of a system; a change in one part of a complex system can cause changes in other parts of the system. can you identify in this environmental story of the Amazon Die-Off.
One environmental variable initiated this cascade of changes. What variable do you think it is and why? HINT: Temperature might seem the most obvious, but what caused the temperature to rise?
Why do you think the changes illustrated in the Amazon Die Off story are drawn in a circle?

Using the Connections Game to act out how complex systems can behave

How can we demonstrate that parts of a system are interconnected and that changes to one part of the system can cause changes to other parts of the system? To help us understand this concept, we are going to play the Connections Game, developed by systems thinkers Rob Quaden, Alan Ticotsky and Debra Lyneis in The Shape of Change. In the Connections Game, you and your fellow students will each be playing one component of a system. What will happen to other components of the system if one component should change?

Connections Game Materials:

Numbered cards large enough to be visible to other students. NOTE: If there are 20 students, cards should be numbered 1-20

Connection Game Instructions: (adapted from The Shape of Change)

1. Demonstration: Understanding the term "equidistant" is critical to playing this game. The teacher will ask two students to help demonstrate what it means to be equidistant from two other players. Can one person move and still be equidistant from the other two people?

2. Your teacher will give each student a number card.

3. Stand in a large circle with your numbers held in front of you so others can see.

4. Look around the room and randomly choose the numbers of two other players. These will be your SECRET equidistant partners. DO NOT tell anyone who they are!

5. When your teacher gives a signal, move to a point that is equidistant from your two partners. Do this with NO talking.

6. Keep playing the game until all players are equidistant from their two partners and the movement stops.

Discuss

Think of the people in the Connections Game circle as a complex system.

How did the system behave when you tried to stay equidistant from your two secret partners?
After destabilizing, did the system eventually reach equilibrium? How do you know?

Feedbacks in complex systems can stabilize or destabilize a system

In complex systems such as the carbon cycle, changes in one environmental variable can cause changes in other variables. Carbon cycle feedbacksinitial change in an environmental variable that causes changes in other variables that then influence the initial environmental change happen when these changes act on the initial change by either amplifying it or slowing it down. Amplyfying feedbacks tend to destabilize a system; feedbacks that slow down or dampen an initial change tend to stabilize a system. In many complex systems, multiple feedbacks are operating. This is especially true in the Arctic where a change to a warmer climate is happening more than twice as fast as anywhere else in the world. Multiple feedbacks are at work in this complex Arctic system, both amplifying and slowing down changes.

Watch the video below on feedbacks in the Arctic. As you watch, make note of the following:

different feedbacks operating in the Arctic (ex. reflectivity)
how a feedback can change from a positive feedback to a negative feedback and then back again in the Arctic environment
the difference between positive feedbacks and negative feedbacks

Why the Arctic is climate changes "canary in the coal mine" - William Chapman
NOTE: If the video does not load, you can watch it here. This link also has questions you can answer that go along with the video by clicking on the THINK—DIG DEEPER—DISCUSS tabs.

Show me more about feedbacks

Feedback loops act on the initial change by amplifying it or dampening it. These loops can be either positive (reinforcing) or negative (balancing).

A positive causal connection is one in which a change (increase or decrease) in some variable results in the same type of change (increase or decrease)in a second variable. In the positive feedback diagram on the right, the variable "increased surface temperature" causes an "increase of evaporation from the oceans."

A negative causal connection is one in which a change (increase or decrease) in some variable results in the opposite change (decrease/increase) in a second variable. In the negative feedback diagram, the increase in "more sunlight reflected back into space" causes a decrease in "surface temperature."

A positive feedback loop (sometimes referred to as a "reinforcing feedback loop"creates conditions that speed up a process and/or amplify the initial change or perturbation. This type of feedback can tend to push a system towards destabilization or even extreme states. Other words and phrases associated with reinforcing feedback loops are vicious circle, snowball effect, domino effect, feeds back in on itself, run-away change, and self-reinforcing loop.

A negative feedback loop' (sometimes referred to as a " balancing feedback loop") creates conditions that slow down and/or dampen the initial change or perturbation. This type or feedback tends to push a system towards stability. Other words and phrases associated with balancing feedback loops are dampening, restores balance, and reducing.

Discussion

Describe a positive (reinforcing) feedback operating in the Arctic
Describe a negative (balancing) feedback operating in the Arctic.
Think about the changes happening in the Arctic. Predict how might these changes might cause other changes in the Arctic biosphere.

Biosphere feedbacks can influence and drive changes in climate; conversely, climate feedbacks can drive changes in the Biosphere.

The Biosphere, comprised of organisms, food webs and ecosystems, is a major component of the carbon cycle. Ecosystem feedbacks may have no influence on climate; however many do. In the following activity, you will use a case study to investigate how carbon cycle feedbacks respond when the biosphere is disrupted by increased infestations of Pine Bark beetles. Before you begin your case study, watch the video below on how feedbacks behave in Biosphere ecosystems. As you watch, make note of:

the types of positive (reinforcing) and negative (balancing) feedbacks that occur; and
feedbacks that shift ecosystems from destabilized states to stabilized states

Feedback Loops - How Nature Gets its Rhythms-Anje-Margreit Neutel NOTE: If the video does not play, you can watch here

When you finish watching, start your case study investigating change in Western pine tree forests ecosystems.

A Case Study: Pine Bark Beetles Infestations and Carbon Cycle Feedbacks

Western forests in both the U.S. and Canada are in trouble. Unusually high Pine Bark Beetle infestations have been causing massive die-offs of pine trees - especially Lodgepole Pine trees. Pine Bark Beetle infestations have been a part of the natural ecology of western forests for a long time. However, the severity and range of the infestations have been increasing. What is causing these changes in beetle infestations and how does the forest carbon cycle respond?

First, find out more about the ecology of Pine Bark Beetles and the causes of increased infestations by clicking on the following links. Then, start your investigation.

Checking In

Show me the materials I will need

Instructions for the Pine Bark Beetle Case Study

1. Draw a circle in the middle of your notebook paper with a diameter of 10 cm (4 inches). If you are using larger paper, scale up the size of the circle. You will be drawing several labels around the outside of the paper so make sure you leave space to write these labels.

2. In groups, choose two or more Case Study scenarios from the list below as per your teacher's instructions. Each scenario will identify environmental variables that are involved in a feedback loop. These variables will be in boldtype. It will be your job to determine cause and effect between environmental variables and what type of feedback loop is operating.

Show me the Carbon Cycle Feedback Scenarios for this activity

Choose two or more of the following Feedback Scenarios:

Scenario One: CO₂, Pine Bark Beetles and wildfires
- The increase of the greenhouse gas carbon dioxide (CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere, combined with drought in some forests, has been creating conditions for increased pine bark beetle infestations. The beetle infestations kill more trees which then dry out. Dry, dead trees are fuel for more wildfires. As they burn, wildfires release greenhouse gases such as carbon dioxide (CO₂), nitrous oxide (N₂O) and methane(CH₄) increasing Earth's surface temperature and warming the atmosphere further.
Scenario Two:: CO₂, Pine Bark Beetles, wildfires and black carbon
- The increase of the greenhouse gas carbon dioxide (CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere, combined with drought in some forests, has been creating conditions for increased pine bark beetle infestations. The beetle infestations kill more trees which then dry out. Dry, dead trees fuel more wildfires. Wildfires release sooty black carbon particles which can linger in the atmosphere for days or weeks before being deposited on the land or ocean far away from their original sources. When black carbon particles fall on ice and snow, the reflectivity of snow and ice is reduced and less sunlight bounces out to space. This increases Earth's surface temperature and warms the atmosphere further.
Scenario Three: CO₂, Pine Bark beetles, wildfires, black carbon and clouds
- The increase of the greenhouse gas carbon dioxide (CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere, combined with drought in some forests, has been creating conditions for increased pine bark beetle infestations. The beetle infestations kill more trees which then dry out. Dry, dead trees fuel more wildfires. Wildfires release sooty black carbon particles which can linger in the atmosphere for days or weeks before being deposited on the land or ocean far away from their original sources. Some black carbon particles increase the growth of stratocumulus clouds which blocks and reduces incoming sunlight. This decreases Earth's surface temperature, cooling the atmosphere.
Scenario Four: CO₂, Pine Bark beetles, wildfires, black carbon and volatile organic compounds(VOCs)
- The increase of the greenhouse gas carbon dioxide (CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere, combined with drought in some forests, has been creating conditions for increased pine bark beetle infestations. The beetle infestations kill more trees which then dry out. Dry, dead trees fuel more wildfires. Wildfires release sooty black carbon particles, greenhouse gases and volatile organic carbon compounds (VOCs). VOCs create a haze that blocks and reduces incoming sunlight. This decreases Earth's surface temperature and cools the atmosphere.
Scenario Five: CO₂, Pine Bark beetles, gross primary production and photosynthesis
- The increase of the greenhouse gas carbon dioxide(CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere has been creating conditions for increased pine bark beetle infestations which are killing many trees in Western Forests. The increase of dead trees in a forest reduces the forest's gross primary productivity which means less CO₂ is being absorbed from the air for photosynthesis. This increases the amount of CO₂ in the atmosphere which then increases Earth's surface temperature, warming the atmosphere further.
Scenario Six: CO₂, Pine Bark beetles, decomposition and soil respiration
- The increase of the greenhouse gas carbon dioxide (CO₂)increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere has been creating conditions for increased pine bark beetle infestations which are killing many trees in Western Forests. Over a decade or so, dead treeseventually fall to the forest floor where they decompose. Increased decomposition increases the rate of soil respiration by soil microbes. Increased soil respiration releases more CO₂to the air which increases Earth's surface temperature, warming the atmosphere further.
Scenario Seven: CO₂, Pine Bark beetles, gross primary production, photosynthesis and forest regeneration.
- The increase of the greenhouse gas carbon dioxide(CO₂) increases Earth's surface temperature, warming the atmosphere. A warmer atmosphere, combined with drought in some forests, has been creating conditions for increased pine bark beetle infestations.The beetle infestations kill more trees which then dry out. Dry, dead trees fuel more wildfires. Wildfires create space for new vegetation and forest regeneration, which can take decades. New vegetation increases the forests' gross primary productivity which means more CO₂_is being absorbed from the air for photosynthesis.This reduces Earth's surface temperature and cools the atmosphere.

3. Read your scenario(s) carefully.

4. Label the outside of the scenario circle with the environmental variables which are in boldtype. The first two variables, CO₂and Earth's surface temperature need to be up at the top. NOTE: At the end of each scenario, the feedbacks will "loop'' back to these two variable. You do not need to write them on the circle again. Abbreviate the variables on your paper if you need to.

5. Draw arrows outside the circle linking the variables.

6. Discuss the type of cause and effect between two sequential variables. Here are your choices:

If an amplified variable causes an amplified effect in the next variable, write (amp/amp) next to the arrow that links the two variables.
If a slowed down/dampened variable causes a slowed down/dampened effect in the next variable, write (slow/slow) next to the arrow that links the two variables.
If a slowed down/dampened variable causes an opposite amplified effect in the next variable, write (slow/amp)next to the arrow that links the two variables.
If an amplified variable causes an opposite slowed down/dampened effect in the next variable, write (amp/slow) next to the arrow that links the two variables.

7. Analyze the feedback loop you have just created from your scenario. Identify the feedback loop as a reinforcing feedback loop (positive feedback) or a balancing feedback loop (negative feedback) and write R or B inside the feedback loop. Here are two hints:

A feedback loop is reinforcing if the initial change (in this case an increase in CO₂) is pushed in the same direction by the feedback loop.
A feedback is balancing if the initial change (in this case an increase in CO₂) is pushed in the opposite direction by the feedback loop.

8. Complex systems such as ecosystems and the carbon cycle have multiple reinforcing( positive feedbacks) and balancing feedbacks (negative feedbacks) operating at the same time. As you analyze your feedback loops, consider the following:

The influence of some feedbacks dominate the influence that other feedbacks have on the system (i.e., some feedbacks are stronger, some are weaker)
Some feedbacks cancel each other out or change from one to another if environmental conditions change.
Some feedbacks operate at different time scales (i.e. days, years, decades, centuries etc.)
Some feedbacks operate at different spatial scales (i.e.,local, regional, continental, hemispheric, global)

Discuss

With your group and the class, discuss the following:

What type of feedback loop is operating in each scenario- Reinforcing or Balancing? Explain why you think so.
Are these feedback loops stabilizing the pine forest carbon cycle or destabilizing the pine forest carbon cycle? Explain why you think so.
Compare and contrast your feedback loops with the class. If you have the space, put them up next to each other on a wall.
- Which feedbacks loops(if any) could cancel each other out?
- Which feedbacks loops (if any) seem weaker or stronger than others? In other words, do the effects of some feedbacks dominate the effects of others?
- Which feedbacks loops operate over shorter timescales? (days, months) Which operate over longer times scales (years, decades+)
- Which feedbacks loops operate over larger spatial scales as opposed to smaller spatial scales? Why?