Feedback Loop: Negative and Positive Feedback Mechanisms

People often request you leave feedback after experiencing something or using any product. Feedback means a reaction or report of some products used or people’s performance. The loop means repeating the same process and instructions in the same system until the process is halted. 

So, a feedback loop is a process where the output of a system is fed as input to the same system, which results in a continuous cycle of information or actions. The occurrence of a feedback loop can have various contexts, including organizations, techniques, as well as individual behavior. An example of feedback loop mechanism is homeostasis in different organisms. 

Another area where the feedback loop plays a significant role is climate change. In climate change positive feed loop accelerates the rate of climate change. The negative feedback loop in the case of climate change helps stabilize the pace of climate change.  

Feedback loop is also termed as self-regulating loop in the living systems. The feedback loop is mainly of two types; positive and negative. In a positive feedback loop, the result of a system reinforces the input resulting in exponential growth or change. But in a negative feedback loop, a system’s output counteracts the information leading to stability or equilibrium.   

It is shown that feedback loop system in case of climate change has worsen the effects. 

Positive Feedback Loop

The feedback mechanism, where the mechanism’s output helps amplify the initial input, results in exponential growth. It is a self-reinforcing process. In short, the positive feedback loop is a cycle that intensifies its effect over multiple repetitions as the output enhances the input. Under different contexts, this rapid change due to the positive feedback mechnism has both; beneficial and detrimental effects. 

Let us understand the beneficial effects of the positive feedback mechanism, which is seen during labor. Here, the oxytocin released from the posterior pituitary gland acts as an input or stimulant of muscle contraction for delivering the baby from the birth canal. Muscle contraction is sharper and stronger due to the release of oxytocin. The contraction intensifies as long as the baby is in the birth canal. Once the baby is out, the stimulus at the receptor ends and oxytocin production decreases, halting the muscle contraction. 

Under certain conditions, a positive feedback loop has many detrimental effects. These damaging effects are observed during the formation of avalanches in the mountains and the increased rate of climate change. 

Let’s discuss the detrimental effect of a positive feedback loop by studying the example of avalanches in the mountains. Avalanche is a mass of snow, ice, soil, rock, and many other materials rapidly moving downward from the hill. Avalanche formation is a feedback system. Here the small amount of snow breaking from the slope of the mountain is the output, which rapidly increases and collects other snow, ice, and different materials during the fall. The increase in size and speed results in the formation of bigger and faster-moving mass now termed an avalanche. 

Negative Feedback Loop

Like a positive feedback loop system, negative feedback mechanisms use output as input for the next cycle. The output now counteracts the initial information, which can result in stability or equilibrium. In simple terms, in the negative feedback loop, the output opposes the input for maintaining balance in the system.  

It is also called a balancing feedback loop. This mechanism is essential in various biological systems and regulating processes in multiple fields. The most common areas where the negative feedback loop plays an important role are body temperature regulation by homeostasis, regulation of blood glucose levels, menstrual cycle in females, and thermostat-controlled heating system. Let us develop deeper understanding on the negative feedback loop by studying two examples; regulation of blood glucose level and thermostat-controlled heating system. 

Thermostat controlled heating system in a building is a great example of a negative feedback loop. Here, a target temperature is set in the system. (dramarnathansdentalcare.com) Once the temperature inside a room falls below the target temperature, the thermostat senses the change and turns on the heating system. Likewise, a rise in temperature above the target temperature triggers the turning off of the heating system. This cycle repeats as needed to maintain room temperature close to the set point.   

The blood glucose levels in humans are regulated with the help of a negative feedback mechanism. The body releases insulin after food consumption because glucose levels rise steeply in the blood. Insulin allows cell glucose absorption from the bloodstream, reducing glucose levels to a certain threshold. This reduction of blood glucose level results in decreased release of insulin. If the blood glucose level reduces too low, another hormone, glucagon, releases that stimulates the liver to release stored glucose. This release of glucose raises blood glucose levels back to the optimal range. These explanations show the importance of a negative feedback loop for maintaining stability and balance within various systems.  

Feedback Mechanism’s Role in Effects of Climate Change

The feedback system plays a significant role in amplifying and dampening the effects of climate change. Climate change occurs mainly through the increase in emissions of greenhouse gas (GHG), primarily carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). The GHG traps heat in the Earth’s atmosphere, leading to global warming. 

Positive feedback loops exacerbate the warming process in climate change, but negative feedback mechanisms partially offset the warming trends. 

Detailed effects of the positive and negative feedback loop in climate change are discussed in the upcoming headings. 

Effect of Positive Feedback System in Climate Change

The positive feedback loop in climate change increases the rate of climate change by feeding into detrimental output as input in the ecosystem. Ice-Albedo feedback, permafrost thawing, forest loss, and carbon sequestration are some of the effects of a positive feedback loop in climate change.  

1. Ice-Albedo feedback: The rise in Earth’s temperature melts glaciers and ice in the Arctic Sea. The melting reduced the planet’s surface area, which was covered by highly reflective ice (high albedo). The dark ocean water and land surfaces with low albedo are exposed, which increases the absorption of solar energy and warms the Earth even more. This warming of Earth results in the melting of more ice, creating a self-reinforcing cycle.  
2. Permafrost thawing: Permanently frozen soil (permafrost) present in the Arctic and subarctic regions starts to thaw once the global temperature rises. The thawing releases a significant amount of methane and carbon dioxide, previously trapped in the frozen ground. Methane is a potent greenhouse gas that further increases global warming. 
3. Forest loss and carbon sequestration: Wildfires and deforestation reduce the capability of Earth to absorb CO₂ by photosynthesis. Forests act as carbon sinks that trap CO₂ from the atmosphere and stores it as biomass. The lower the absorption of CO₂ due to the loss of forests, the higher the atmospheric CO₂ levels, increasing global warming. 

Effect of Negative Feedback Loop in Climate Change

The negative feedback loop helps in the slight remediation of the effects of climate change. 

1. Carbon uptake by Oceans: Oceans can absorb large amounts of CO2 from the atmosphere and act as carbon sinks. But increasing the amount of CO2 in the atmosphere results in less carbon absorption by the ocean, decreasing the efficiency of the negative feedback loop.    
2. Enhanced plant growth: Increased CO₂ level enhances plant growth in some ecosystems. The plant growth can absorb more carbon from the atmosphere. Nutrient availability, water availability, and weather conditions significantly affect the effectiveness. 

Although the negative feedback mechanism can slightly mitigate some climate change effects, it can be overwhelming due to the more robust positive feedback loops. For instance, the ability of oceans to absorb carbon is limited due to ocean acidification. This acidification negatively impacts the ocean ecosystems. As a result, the net effect of different feedback loops can increase the rate of global warming and its impact on various ecosystems. Effective methods of bioremediation is required for controlling climate change.

References

• Lippa, A. M., & Goulian, M. (2009). Feedback inhibition in the PhoQ/PhoP signaling system by a membrane peptide. PLoS genetics, 5(12), e1000788. https://doi.org/10.1371/journal.pgen.1000788 
• Dickinson, R.E. and Hanson, B. (1984). Vegetation-Albedo Feedbacks. In Climate Processes and Climate Sensitivity (eds J.E. Hansen and T. Takahashi). https://doi.org/10.1029/GM029p0180
• Rao, S.D. and Igoshin, O.A. (2021) ‘Overlaid positive and negative feedback loops shape dynamical properties of phopq two-component system’, PLOS Computational Biology, 17(1). doi:10.1371/journal.pcbi.1008130.