Positive Feedback Cycles in Global Warming
- A positive feedback cycle in global warming occurs when an initial increase in temperature triggers processes that further enhance warming.
- These feedback loops amplify climate change, making it more severe and accelerating the rate of global temperature rise.
- Unlike negative feedback, which stabilizes a system, positive feedback reinforces change, making it more difficult to reverse.
- Several natural processes contribute to positive feedback cycles in global warming.
Definition
Positive feedback loop
A process where an initial change causes further changes that amplify the original effect, making it stronger and self-reinforcing.
- Think of positive feedback like a snowball rolling down a hill.
- As it rolls, it picks up more snow, growing larger and moving faster.
- The initial push (warming) sets off a chain reaction that amplifies the effect.
Key Positive Feedback Cycles in Global Warming
1. Release of Carbon Dioxide from the Deep Ocean
- Warming Oceans: As the atmosphere warms, so do the oceans.
- Reduced Solubility: Warmer water holds less carbon dioxide ($CO_2$), causing it to be released back into the atmosphere.
- Amplified Warming: This additional $CO_2$ enhances the greenhouse effect, further warming the planet.
- Imagine opening a soda can on a hot day.
- The gas escapes more quickly because warm liquids hold less dissolved gas.
- Similarly, warmer oceans release more $CO_2$.
2. Loss of Reflective Snow and Ice (Albedo Effect)
Definition
Albedo
Albedo ($\alpha$) measures the reflectivity of a surface.
- Albedo Effect: Snow and ice reflect sunlight, keeping the Earth cooler.
- Melting Ice: As global temperatures rise, ice melts, exposing darker surfaces like ocean water or land.
- Increased Absorption: These darker surfaces absorb more solar radiation, leading to further warming and more ice melt.
- The albedo effect is a critical concept.
- Remember: high albedo means more reflection (cooling), while low albedo means more absorption (warming).
3. Accelerating Decomposition in Peat and Permafrost
Definition
Permafrost
Ground that remains frozen for two or more consecutive years, typically found in polar regions.
- Peatlands and Permafrost: These areas store vast amounts of organic carbon.
- Warming Temperatures: Higher temperatures accelerate the decomposition of organic matter, releasing $CO_2$ and methane ($CH_4$).
- Amplified Greenhouse Effect: Methane is particularly potent, trapping much more heat than $CO_2$.
- Don't confuse $CO_2$ and $CH_4$.
- While both are greenhouse gases, methane is approximately 25 times more effective at trapping heat over a 100-year period.
4. Methane Release from Melting Permafrost
- Frozen Methane: Permafrost contains methane hydrates where methane is trapped in ice.
- Thawing Permafrost: As permafrost melts, these hydrates break down, releasing methane into the atmosphere.
- Rapid Warming: This creates a powerful feedback loop, as methane significantly accelerates warming.
Methane hydrates are sometimes called "frozen time bombs" because of their potential to release large amounts of methane if destabilized.
5. Increases in Droughts and Forest Fires
- Drier Conditions: Warming increases the frequency and severity of droughts.
- More Fires: Droughts make forests more susceptible to fires, which release stored carbon into the atmosphere.
- Reduced Carbon Sequestration: Burned forests can no longer absorb $CO_2$, further amplifying warming.
The 2020 Australian bushfires released an estimated 900 million tonnes of $CO_2$, equivalent to nearly double the country's annual emissions.
Why Do Positive Feedback Cycles Matter?
- Acceleration of Warming: These cycles make it harder to stabilize global temperatures.
- Tipping Points: They can push the Earth's climate system toward irreversible changes, such as the collapse of ice sheets or the dieback of rainforests.
- Global Impacts: Amplified warming affects ecosystems, weather patterns, and human societies.
- How do positive feedback cycles challenge our ability to predict and manage climate change?
- Consider the role of uncertainty in scientific models.
Addressing Positive Feedback Cycles
- Mitigation: Reducing greenhouse gas emissions is critical to slowing these feedback loops.
- Adaptation: Strategies like restoring peatlands or increasing forest resilience can help reduce the impact of these cycles.
- Innovation: Technologies such as carbon capture and storage (CCS) offer potential solutions for removing $CO_2$ from the atmosphere.
Which positive feedback cycle do you think poses the greatest threat? Why?
Self review- What is a positive feedback cycle, and how does it contribute to global warming?
- How does the release of methane from permafrost accelerate global warming?
- Explain the role of decreasing ice and snow cover in amplifying global warming.
- Why are forest fires considered a positive feedback mechanism in climate change?
