Climate change: exam questions

Answer: B – ring width depends on other factors as well as temperature and rainfall.

• peat is acidic / anaerobic / waterlogged so pollen is preserved (and does not decay) (1)
• cores are taken and layers (of different depths) are dated, for example by radiocarbon dating (1)
• pollen grains are identified and counted in each layer (1)
• different plant species need different conditions, so the species present show the climate at that time (accept cold-adapted vs warm-adapted species) (1)
• change in the pollen types with depth shows change in climate over time (1)
• Max 4

• both rise together / positive correlation (1)
• a correlation does not prove cause; another factor could affect both (1)
• the greenhouse effect gives a mechanism (CO₂ absorbs infra-red radiation) so a causal link is plausible (accept data from several independent sources / ice cores) (1)
• only three data points / limited data / temperature rose by more between 1950 and 2000 than before (1)
• Max 3

• short-wavelength radiation from the Sun passes through the atmosphere and warms Earth’s surface (1)
• Earth emits longer-wavelength infra-red radiation (1)
• greenhouse gases absorb the infra-red radiation and re-radiate it back to Earth’s surface (1)
• burning fossil fuels / deforestation increases carbon dioxide (accept methane from cattle / rice paddies) (1)
• so more infra-red is trapped (enhanced greenhouse effect) (1)
• Max 4

• planting trees / afforestation increases photosynthesis (1)
• so more carbon dioxide is removed from the atmosphere and carbon is stored in wood (1)
• burning fewer fossil fuels / using renewable energy reduces combustion (1)
• so less carbon is released from the fossil fuel store (1)
• other valid methods, for example protecting peat bogs / forests, using biofuels with explanation (up to 2)
• Max 4

• climate is a complex system with many variables / interacting factors (1)
• so not all can be included accurately / small errors in data are amplified (1)
• feedback loops are difficult to predict, for example melting ice reduces reflection of heat (1)
• predictions depend on assumptions about future emissions / extrapolation assumes the trend continues (1)
• data are incomplete / not available for all areas (1)
• Max 3

• mean temperatures have increased, so the area with suitable abiotic conditions has moved north (1)
• the butterfly (and its food plants) can now survive / reproduce further north (1)
• higher temperatures speed up enzyme-controlled reactions in development (1)
• so pupae develop faster and adults emerge earlier (accept earlier spring) (1)
• if food plants do not respond in the same way, there may be a mismatch in timing (1)
• Max 4

• the company may have a vested interest / financial interest in fossil fuels (1)
• the report may use selected data / not include all the evidence (1)
• check whether it has been peer reviewed / published in a scientific journal (1)
• compare with data from independent sources / other scientists’ research (1)
• check the authors’ expertise / who funded the research (1)
• Max 4

• biofuels may be close to carbon neutral, because the CO₂ released was absorbed by the crop in photosynthesis (1)
• they replace fossil fuels, so less carbon is released from the fossil store (1)
• clearing forest releases stored carbon as CO₂ (by burning and decay) (1)
• forests are removed so fewer trees to remove CO₂ / loss of carbon sink (1)
• loss of habitats and biodiversity / monoculture supports fewer species (1)
• fertiliser, machinery and processing use energy / release greenhouse gases (1)
• valid judgement, for example better to use waste material or poor land / reforestation (1)
• Max 5