Year 10 Science · Unit 4 · Lesson 7
Challenge Worksheet
Learning Goals
Read the graph
The graph models the cumulative cost of two coastal adaptation options for a 200-house town over 60 years. The sea-wall line steps up each time the wall is rebuilt and raised; the managed-retreat line rises during a 10-year buyout, then levels off. Use the data shown to answer the questions below.
Cumulative Cost of Two Coastal Adaptation Strategies (model)
Note: a simplified teaching model. Real cost projections vary with property values, sea-level scenarios and discount rates.
(a) Using the graph, describe what happens to the cumulative cost of each strategy over the 60 years. Identify the approximate year at which the sea wall first needs rebuilding.
(b) Over this 60-year window the sea wall is far cheaper than managed retreat. Explain why a council might still reasonably choose managed retreat despite the graph. What does the graph NOT show about the sea-wall option?
(c) The managed-retreat line is flat after year 10, but the sea-wall line keeps stepping upward forever. Extrapolate: at roughly what point would the two strategies cost the same, and what does this tell you about comparing strategies over very long timescales?
Limits to adaptation
Context
The IPCC distinguishes "hard limits" to adaptation (physical or biological constraints that cannot be overcome by any management or technology) from "soft limits" (overcome with enough money, technology or governance). The lesson gives three Australian examples of hard limits: the Great Barrier Reef above ~2°C of warming, mountain glaciers, and low-lying island nations such as Tuvalu.
(a) Choose ONE of the three examples above. Explain precisely why it represents a hard limit, not a soft limit, that adaptation cannot solve.
Someone claims...
"Spending money on adaptation, sea walls, drought-resistant crops, cooling centres, is just giving up on solving climate change. If we admit we have to adapt, we are admitting defeat. We should put every dollar into cutting emissions instead and stop wasting money preparing for a disaster we can still prevent."
(a) Identify the part of this claim that contains a reasonable point, and explain why mitigation is genuinely important.
(b) Explain why the claim is misleading. Use the idea that some climate change is already "locked in" and refer to a specific adaptation that protects people right now.
(c) Scientists summarise the relationship as: "Avoid the unmanageable, and manage the unavoidable." Explain how mitigation and adaptation work together, and why focusing on only one of them would leave communities worse off.
Wrap Up
In one sentence, what was the main idea of this lesson?
Warm Up, Read the graph
(a) Managed retreat rises steeply over the first 10 years to about $60 million, then stays flat (no further cost). The sea wall starts low (about $3 million) and steps upward each time it is rebuilt and raised, reaching roughly $9 million by year 50 but continuing to climb. The sea wall first needs rebuilding at about year 25. [2 marks]
(b) The graph only shows cost over 60 years. It does not show: the risk of catastrophic failure if a wall is overtopped, ongoing maintenance and erosion of neighbouring beaches, that costs keep rising indefinitely beyond year 60, or the safety benefit of permanently removing people from the danger zone. A council may choose managed retreat to guarantee long-term safety, avoid an ever-rising cost treadmill, and prevent locking future generations into a high-risk location. [3 marks]
(c) Extrapolating the stepped sea-wall line upward, it would eventually reach $60 million and overtake managed retreat far beyond year 60 (well into the next century at ~$3 million per 25-year cycle). This shows that the "cheaper" strategy depends entirely on the timescale chosen: over very long horizons the one-off retreat cost beats the never-ending wall cost. [2 marks; accept any reasonable extrapolated estimate with justification]
Go Deeper, Limits to adaptation
(a) Sample (Great Barrier Reef): Above about 2°C of global warming, tropical sea-surface temperatures regularly exceed the thermal tolerance of the coral-zooxanthellae symbiosis, triggering mass bleaching too often for reefs to recover. No local action (improving water quality, shading, coral gardening) can lower the temperature of the whole ocean, so it is a hard physical/biological limit, not a soft limit that money or technology could fix. (Glaciers: once small enough they enter unstoppable accelerating melt. Low-lying islands: at some sea level the entire territory is submerged, no wall is high enough.) [3 marks: identifies example + states the physical/biological constraint + explains why technology/resources cannot overcome it]
Evaluate the Claim
(a) Reasonable point: mitigation (cutting emissions) is genuinely vital because it limits total warming and keeps more systems below their hard adaptation limits, the less we warm, the less adaptation we will need. [2 marks]
(b) Misleading because a significant amount of warming and sea-level rise is already "locked in" from past emissions, so harm is happening now regardless of future emission cuts. Adaptation is not surrender, it protects people from changes that mitigation can no longer prevent. Example: heat health warning systems and cooling centres (introduced after the 2009 Melbourne heatwave that killed 374 people) save lives today; emission cuts cannot help those people this summer. [3 marks]
(c) Mitigation reduces how much future climate change occurs ("avoid the unmanageable"); adaptation reduces harm from the change already committed ("manage the unavoidable"). Relying only on mitigation leaves communities exposed to impacts already locked in (heatwaves, sea-level rise) with no protection. Relying only on adaptation lets warming run unchecked until systems pass hard limits (reefs collapse, islands drown) that no adaptation can manage. Both are needed: more mitigation reduces the adaptation burden, and adaptation buys time and safety while emissions fall. A strong answer notes that the two are complementary, not alternatives. [4 marks]