Key Idea: Most marks in topic 6.2 come from the impacts of climate change on ecosystems and on societies, then feedbacks. At HL, also learn climate models, scenarios, tipping points and climate justice.
1. Impacts on ecosystems (most marks)
- Warmer seas bleach corals: the Great Barrier Reef bleached in 2016, 2017, 2020, 2022 and 2024.
- Species shift towards the poles and uphill; those with nowhere to go can die out.
- Melting sea ice cuts krill, so penguins and seals lose food; more droughts and wildfires.
2. Impacts on societies
- Rising seas flood low coasts and islands, such as Tuvalu and Bangladesh.
- Stronger storms: Hurricane Maria wrecked Dominica's crops and homes in 2017.
- Farming and water suffer from drought and glacier loss; some cold places gain longer seasons.
3. Causes, feedbacks and HL ideas
- Carbon dioxide at Mauna Loa rose from about 317 ppm in 1960 to about 427 ppm in 2025: the Keeling curve.
- Positive feedback: melting ice exposes dark sea, which absorbs more heat and melts more ice.
- At HL: climate data and models, scenarios, tipping points and cascades, and responsibility versus vulnerability.
How it is examined:
| Question | How to score |
|---|---|
| [1] to [2] Describe a trend in a climate graph | Direction, years and numbers, with units. |
| [2] Outline two impacts on a named species or place | Name the climate change, then its effect. |
| [4] to [7] Explain feedbacks in global warming | Name the loop, positive or negative, step by step. |
| [7] Explain impacts on ecosystems or societies | Several impacts, each with a mechanism and an example. |
| [9] Discuss impacts on food or societies | Harms and some benefits, named places, a judgement. |
Key terms, one line each:
| Term | In one line |
|---|---|
| Enhanced greenhouse effect | extra warming from greenhouse gases released by people |
| Climate | the average weather of a place over about 30 years |
| Positive feedback | a change that makes itself bigger, such as melting ice |
| Negative feedback | a change that reduces itself and keeps the system stable |
| Coral bleaching | corals losing their algae in warm water and turning white |
| Tipping point | a threshold after which a system shifts to a new state and may not come back |
| Tipping cascade | one tipping point setting off others, like dominoes |
Last-minute check: answer, then tap to see.
Which ice sheets may tip at only about 1.5 °C? Greenland and West Antarctica.
How could Greenland's melt affect the Amazon? Fresh water slows the Atlantic currents, shifting rain belts: a cascade.
Why are scenarios not forecasts? They show possible futures; which happens depends on our choices.
Why is Tuvalu vulnerable but not responsible? Tiny emissions, but low land and little money to adapt.
Some scientists warn that warming could push the Amazon rainforest past a tipping point. Explain how a tipping cascade could follow.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Exam tips
- Link each impact to the change that causes it: warmer water, rising seas, drought or storms.
- Use named places and species: the Great Barrier Reef, Tuvalu, Dominica.
- For a feedback, say whether it is positive or negative and explain the loop.
- For tipping points, say the change is hard or impossible to reverse.