Question 1
Paper 1A style
Which is an example of a positive feedback cycle in global warming?
- Increased photosynthesis by trees absorbs more CO₂
- Melting ice exposes darker surfaces that absorb more solar radiation
- Warmer oceans increase upwelling of nutrients
- More cloud reflects sunlight back into space
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Answer: B [1]
Question 2
Paper 1A style
What is the cause of coral bleaching?
- Ocean acidification dissolving coral skeletons
- Microplastics blocking coral polyps
- Increased water temperature causing corals to expel their symbiotic algae
- Reduced upwelling of nutrients
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Answer: C [1]
Question 3
Paper 1B style
The table shows the annual mean concentration of atmospheric carbon dioxide measured at Mauna Loa Observatory, Hawaii (values rounded to the nearest ppm). (a) Calculate the percentage increase in CO₂ concentration from 1960 to 2020. [2] (b) Compare the rate of increase between 1960–1980 and 2000–2020. [1] (c) Outline two anthropogenic causes of the increase. [2]
| Year | CO₂ concentration / ppm |
|---|---|
| 1960 | 317 |
| 1980 | 339 |
| 2000 | 370 |
| 2020 | 414 |
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- (a) (414 − 317) ÷ 317 × 100 [1]
- (a) 30.6% / 31% [1]
- (b) rate doubled / 22 ppm per 20 years in 1960–1980 compared with 44 ppm per 20 years in 2000–2020 [1]
- (c) combustion of fossil fuels, e.g. coal / oil / natural gas [1]
- (c) deforestation / burning of forests, reducing CO₂ uptake and releasing CO₂ [1]
- (c) cement production [1]
- max 5
Question 4
Paper 2A style
Explain how early breakout of landfast ice threatens emperor penguins.
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- emperor penguins breed on landfast ice / ice attached to the coast [1]
- chicks need stable ice until they have grown waterproof feathers [1]
- early breakout causes chicks to drown / die of cold [1]
- breeding grounds lost / breeding fails / population falls [1]
- max 3
Question 5
Paper 2B style
Explain how climate change could cause boreal forests to change from net carbon accumulation to net carbon loss.
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- boreal forests / taiga currently store more carbon than they release / carbon sink [1]
- warmer temperatures [1]
- decreased winter snowfall / less spring meltwater [1]
- increased incidence of drought [1]
- reduced primary production / less photosynthesis so less CO₂ absorbed [1]
- forest browning / trees die [1]
- more frequent and intense forest fires [1]
- combustion of legacy carbon / old soil organic matter releases CO₂ [1]
- positive feedback: released CO₂ causes further warming [1]
- this is a tipping point / change becomes self-sustaining OWTTE [1]
- max 6
Question 6
Paper 2A style
Explain how warmer surface water can reduce energy flow through marine food chains.
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- warm surface water forms a stable layer that does not mix with deeper water [1]
- prevents upwelling of nutrients / nitrate / phosphate to the surface [1]
- phytoplankton growth / ocean primary production decreases [1]
- less energy available to consumers such as fish / seabirds [1]
- max 3
Question 7
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanUsing the example of great tits and caterpillars in north European forests, explain how climate change can disrupt the synchrony of phenological events.
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- phenology is the timing of biological events [1]
- caterpillar emergence / peak biomass is cued by temperature / leaf budburst [1]
- great tit breeding / laying date relies partly on photoperiod / changes less [1]
- warmer springs make caterpillar peak earlier [1]
- chicks hatch after the peak food supply / mismatch [1]
- fewer chicks survive / lower breeding success [1]
- max 4
Question 8
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how reduced snow cover has caused evolution in the tawny owl (Strix aluco).
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- tawny owls have heritable grey and brown colour variants [1]
- grey owls had higher survival / fitness in snowy winters (better camouflaged) [1]
- with less snow, brown owls have higher fitness than before / survive and reproduce more [1]
- frequency of brown owls / allele for brown colour increases in the population [1]
- max 3