Climate feedbacks and tipping points: WACE Year 12 Earth and Environmental Science
“Explain positive and negative climate feedbacks and the concept of tipping points”
A feedback is a process triggered by warming or cooling that then amplifies it (positive feedback) or dampens it (negative feedback). Positive feedbacks such as the ice-albedo, water-vapour and permafrost-methane feedbacks make warming worse, while some negative feedbacks resist change. Because positive feedbacks dominate, a small forcing can be amplified into large change, and crossing a tipping point can lock in change that is hard to reverse.
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.
The major climate feedbacks, ice-albedo, water vapour and permafrost carbon release, are positive, so they amplify warming. This is why a relatively modest forcing can produce a large temperature response, and why feedbacks are central to projecting how much the climate will change.
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.
Forcing: an external factor that drives climate change. Feedback: an internal process triggered by change that amplifies or dampens it. Positive feedback: amplifies the original change. Negative feedback: dampens the original change. Tipping point: a threshold beyond which change becomes self-sustaining or irreversible.
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.
For the ice-albedo feedback, set out the loop. Warming melts ice; less ice means lower albedo, so more sunlight is absorbed; more absorption causes more warming; more warming melts more ice. Identify it as a positive feedback because each step reinforces the last, and note it amplifies the original forcing.
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.
- Confusing forcing and feedback
- A forcing starts the change; a feedback is the system's triggered response.
- Calling all feedbacks positive
- Some are negative and oppose change, though weaker overall.
- Saying positive feedback means good
- Positive means amplifying, not beneficial.
- Treating tipping points as gradual
- They are thresholds beyond which change can become self-sustaining and hard to reverse.
Exam-style questions
Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
WACE 2022-style7 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 2020-style6 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.