How do feedbacks amplify or dampen climate change, and what are tipping points?
Explain positive and negative climate feedbacks and the concept of tipping points
A focused answer to the WACE Year 12 Earth and Environmental Science dot point on climate feedbacks. Covers positive feedbacks such as ice-albedo, water vapour and permafrost methane, negative feedbacks, the distinction between forcing and feedback, and tipping points, with worked reasoning.
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What this dot point is asking
SCSA wants you to explain positive and negative feedbacks and the idea of tipping points, distinguishing feedbacks from the forcings that start the change. Feedbacks are why small pushes, whether orbital or human, produce large climate responses.
Forcing versus feedback
First separate two ideas.
- A forcing is an external factor that pushes climate to change, such as rising carbon dioxide or an orbital shift.
- A feedback is a process within the climate system that the change itself triggers, which then either amplifies (positive) or reduces (negative) the original change.
Positive feedbacks
Positive feedbacks reinforce the initial change, making warming worse.
- Ice-albedo feedback. Warming melts reflective ice, exposing darker ocean or land that absorbs more sunlight, causing further warming and more melting.
- Water-vapour feedback. A warmer atmosphere holds more water vapour, itself a greenhouse gas, which traps more heat and warms further.
- Permafrost feedback. Warming thaws frozen ground, releasing stored carbon dioxide and methane, which adds to warming.
Negative feedbacks
Negative feedbacks oppose the change, helping stabilise climate, though they are generally weaker than the positive ones.
- Increased warming raises infrared emission to space, shedding some heat.
- Some changes in cloud cover can reflect more sunlight and offset warming, though cloud feedbacks are complex and uncertain.
Tipping points
A tipping point is a threshold where a small additional change pushes part of the climate system into a new state that is hard to reverse.
- Once past the threshold, positive feedbacks can drive the change even if the original forcing stops.
- Examples discussed in climate science include the collapse of major ice sheets, large-scale permafrost thaw, and shifts in ocean circulation.
- Because the changes can be effectively irreversible on human timescales, tipping points are a key reason for limiting warming.
Why feedbacks matter for prediction
Feedbacks determine how much warming results from a given increase in greenhouse gases, so they are central to climate models. Because positive feedbacks amplify the initial forcing and tipping points threaten abrupt, lasting change, understanding feedbacks underpins both the urgency of mitigation and the uncertainty in projections.