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.
Why feedbacks make projections uncertain
Feedbacks are the main reason climate projections come as a range rather than a single number, and explaining this earns marks in evaluation questions. The direct warming from a doubling of carbon dioxide is fairly well known from physics; the uncertainty lies in how strongly the feedbacks respond. Water-vapour and ice-albedo feedbacks are well understood and clearly positive, but cloud feedbacks are genuinely uncertain because warming changes both the amount and type of cloud, and different cloud changes can either amplify or dampen warming. Carbon-cycle feedbacks (how much extra carbon permafrost and warming soils release, and how ocean and forest sinks weaken) add further uncertainty. Because these feedbacks multiply the initial forcing, even small differences in their strength produce large differences in projected warming. This is why models report a likely range, and why the existence of net-positive feedback, rather than its exact value, is the robust conclusion that justifies precautionary mitigation.
Exam-style practice questions
Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WACE 20227 marksExplain the difference between positive and negative climate feedbacks, giving an example of each, and explain why the dominance of positive feedbacks means a modest forcing can produce a large climate change.Show worked answer →
A 7 mark answer needs both feedback types with examples and the amplification argument.
- Positive feedback (amplifies)
- Example, ice-albedo: warming melts reflective ice, exposing darker ocean or land that absorbs more sunlight, causing further warming and more melting, a self-reinforcing loop. Water-vapour feedback is another (warmer air holds more water vapour, a greenhouse gas, adding warming).
- Negative feedback (dampens)
- Example: a warmer surface emits more infrared radiation to space, shedding some heat and partly opposing the warming. Some cloud responses can also reflect more sunlight, though cloud feedbacks are uncertain.
- Why amplification
- Because the major feedbacks (ice-albedo, water vapour, permafrost carbon) are positive and outweigh the negatives, the initial change is reinforced rather than cancelled. So even a modest forcing (such as a given rise in carbon dioxide) is amplified through these loops into a much larger temperature response than the forcing alone would cause.
Markers reward correct examples of each feedback type and the point that net-positive feedback amplifies a small forcing into large change.
WACE 20206 marksExplain what is meant by a climate tipping point and discuss why tipping points are a particular concern for climate management.Show worked answer →
A 6 mark answer needs the tipping-point concept and why it matters.
Concept. A tipping point is a threshold beyond which a part of the climate system shifts into a new state that is difficult or impossible to reverse on human timescales. Once crossed, positive feedbacks can drive the change to continue even if the original forcing stops.
Concern for management. Tipping points matter because change can become self-sustaining and effectively irreversible (for example large ice-sheet collapse and the resulting sea-level rise, runaway permafrost methane release, or a shift in ocean circulation). This means warming may not be smoothly reversible by later cutting emissions, and the exact thresholds are uncertain, so we cannot be sure how close they are. This combination of irreversibility and uncertainty is a strong argument for limiting warming now (precaution), rather than assuming change can be undone later.
Markers reward the threshold/irreversibility definition with a feedback link and a clear discussion of why irreversibility plus uncertainty drives precautionary mitigation.