• Quick retrieval from earlier learning (Analyse climate data: CO₂ records and temperature trends). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Annual mean CO₂ at the Mauna Loa observatory was about 369 ppm in 2000 and about 421 ppm in 2023. What was the mean rate of increase, in ppm per year? Give 1 decimal place. → 2.3Prompt: rate = change in CO₂ ÷ change in time
2. The CO₂ record from Mauna Loa rises every year but also goes up and down within each year. Why the yearly wiggle? (Volcanoes erupt every winter / Northern Hemisphere plants absorb CO₂ in spring and summer and release it in autumn and winter / The instruments are faulty / People burn no fuel in summer) → Northern Hemisphere plants absorb CO₂ in spring and summer and release it in autumn and winterPrompt: Most land, and so most plants, is in the Northern Hemisphere.
3. Climate evidence: which statement is NOT true? (Arctic sea ice in summer has shrunk since satellite records began in 1979. / Melting sea ice is the main cause of sea-level rise. / Global average surface temperature has risen by more than 1 °C since the late 1800s. / Burning fossil fuels is the main cause of the recent rise in atmospheric CO₂.) → Melting sea ice is the main cause of sea-level rise.Prompt: What is the difference between weather and climate?

• Show today's forecast and ask what it means for the class and how forecasters know.
• Share the objective: Climate feedbacks and natural climate cycles. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Is this a positive or negative climate feedback: more CO₂ boosts plant growth, which takes up some CO₂?
• Step 1: A negative feedback works against the initial change.
• Step 2: So the answer is: negative feedback (reduces warming)
• Answer: negative feedback (reduces warming)
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Is this a positive or negative climate feedback: warmer air holds more water vapour, a greenhouse gas? (positive feedback (amplifies warming) / negative feedback (reduces warming)) → positive feedback (amplifies warming)Prompt: Does the effect cause more warming or less?
2. Open ocean has an albedo of 0.06 (it reflects that fraction of sunlight). If 300 W/m² of sunlight arrives, how much is absorbed, in W/m²? → 282 W/m²Prompt: Absorbed fraction = 1 − albedo.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Why can Milankovitch cycles not explain today's warming? (They act over thousands of years, but today's warming has happened in about 150 years / They only affect Mars / They cause cooling only / They stopped working in 1900) → They act over thousands of years, but today's warming has happened in about 150 yearsPrompt: Compare the time scales.
2. Is this a positive or negative climate feedback: melting ice exposes darker ocean that absorbs more sunlight? (positive feedback (amplifies warming) / negative feedback (reduces warming)) → positive feedback (amplifies warming)Prompt: Does the effect cause more warming or less?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-12.