• 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 354 ppm in 1990 and about 414 ppm in 2020. What was the mean rate of increase, in ppm per year? Give 1 decimal place. → 2Prompt: 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? (People burn no fuel in summer / The instruments are faulty / Northern Hemisphere plants absorb CO₂ in spring and summer and release it in autumn and winter / Volcanoes erupt every winter) → 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? (Sea level is rising as oceans warm and land ice melts. / Arctic sea ice in summer has shrunk since satellite records began in 1979. / Global average surface temperature has risen by more than 1 °C since the late 1800s. / A cold winter in one city disproves global warming.) → A cold winter in one city disproves global warming.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: a warmer Earth radiates more energy to space? (positive feedback (amplifies warming) / negative feedback (reduces warming)) → negative feedback (reduces warming)Prompt: Does the effect cause more warming or less?
2. Fresh snow has an albedo of 0.85 (it reflects that fraction of sunlight). If 400 W/m² of sunlight arrives, how much is absorbed, in W/m²? → 60 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. 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. Why might a "tipping point" in the climate system be especially worrying? (Past a threshold, change can become self-sustaining and hard to reverse / It makes the climate change back instantly / It reduces sea level / It only affects weather for one day) → Past a threshold, change can become self-sustaining and hard to reversePrompt: Think about ice sheets once they start to collapse.

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