Key Idea: Most marks in topic 6.2 come from the impacts of climate change on ecosystems and on societies. Then learn feedbacks, the Keeling curve and the climate planetary boundary.
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 and feedbacks
- 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.
- The climate planetary boundary is 350 ppm of carbon dioxide; we passed it in 1988.
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 |
Last-minute check: answer, then tap to see.
Why do corals bleach in a heatwave? They expel their algae, which feed them, so they starve.
Is ice melting a positive or negative feedback? Positive: less ice, less reflection, more warming.
Where has carbon dioxide been measured since 1958? Mauna Loa, Hawaii: the Keeling curve.
Name one possible benefit of climate change. Longer growing seasons in cold places, such as Canada.
In the Arctic, sea ice in September now covers far less ocean than it did in 1980. Explain how this can speed up global warming.
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 a [9], give harms and some benefits, then a judgement.