Climate change — Edexcel International A Level Biology
Evidence for and causes of climate change, the carbon cycle, models, effects on organisms, and the conflict between human needs and conservation.
Revision notes
7 short notes, in the order of the specification. Each one in short:
Evidence for past and present climate change comes from direct records of carbon dioxide levels and temperature, and from indirect evidence such as pollen preserved in peat bogs and the width of tree rings (dendrochronology). Climate change is judged by recognising correlations and then deciding whether the evidence also shows a causal relationship.
Anthropogenic climate change is caused by human activities that raise concentrations of greenhouse gases. The greenhouse effect occurs when gases such as carbon dioxide and methane absorb long-wavelength infra-red radiation emitted by Earth and re-radiate it, warming the lower atmosphere. More greenhouse gases enhance this effect and cause global warming.
In the carbon cycle, carbon dioxide is removed from the atmosphere by photosynthesis and dissolving in oceans, and is returned by respiration, decomposition and combustion. Methods to reduce atmospheric carbon dioxide act on these processes: increasing carbon stored in plants and soils, protecting carbon sinks, and burning less fossil fuel.
Extrapolation extends a trend in existing data beyond the range measured to make predictions, and these predictions are built into mathematical models of future climate change. Models have limitations: the climate is a complex system with many interacting factors and feedback loops, data are incomplete, and predictions depend on assumptions about future emissions.
Climate change alters temperature, rainfall patterns and the timing of the seasons. These changes affect where species can live, so distributions shift towards the poles or to higher altitude, and they alter development and life cycles, for example the timing of flowering, hatching and migration. Species with different responses can become out of step.
Scientific conclusions about controversial issues, such as how much humans are affecting climate change and what should be done, can depend on who reaches them. Individuals and organisations may have vested interests, select data or use different assumptions. Evidence should be judged by checking the source, the funding, peer review and whether the conclusion matches the data.
Humans need resources such as timber, food and fuel, but using them can damage ecosystems. Reforestation and the use of sustainable resources, including biofuels, are examples of effective management of this conflict. A resource is sustainable if it is replaced as fast as it is used, so that it is available for future generations.
Exam questions
9 exam-style questions (32 marks), each with its mark scheme.
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21 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of energy flow, ecosystems and the environment on one page, so you can see where this subtopic fits.
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Quick check questions
Name two sources of indirect evidence for past climates.
Show answer
Pollen in peat bogs and tree rings (dendrochronology). Ice cores are also acceptable.
What is an anthropogenic cause of climate change?
Show answer
One caused by human activity, such as burning fossil fuels or deforestation.
Which processes in the carbon cycle remove CO₂ from the atmosphere?
Show answer
Photosynthesis and dissolving in the oceans.
State one limitation of climate models.
Show answer
Climate is a complex system with feedback loops that cannot all be included accurately.
Why might the conclusions about climate change differ between organisations?
Show answer
Vested interests, funding or selection of data can influence the conclusions.
Frequently asked questions
What evidence is there for climate change?
Evidence includes direct records of atmospheric carbon dioxide and global temperature, and indirect evidence such as pollen preserved in peat bogs and tree ring widths (dendrochronology). Together these show past and present changes, and the correlation between carbon dioxide and temperature is supported by the greenhouse effect mechanism.
How do greenhouse gases cause global warming?
Greenhouse gases such as carbon dioxide and methane absorb infra-red radiation emitted by Earth’s warmed surface and re-radiate it, some back to the surface. Higher concentrations from human activities trap more heat, so the lower atmosphere warms. This is the enhanced greenhouse effect.
How can the carbon cycle be used to reduce atmospheric carbon dioxide?
Methods increase removal or reduce release. Planting trees raises photosynthesis, protecting forests and peat bogs keeps carbon stored, and replacing fossil fuels with renewable energy or biofuels reduces combustion. Each method acts on a specific stage of the carbon cycle.
What are the limitations of climate models?
Climate is a complex system with many interacting factors and feedback loops that cannot all be modelled accurately. Data may be incomplete, and predictions depend on assumptions about future emissions. Extrapolation also assumes that the current trend will continue, which may not happen.
How does climate change affect plants and animals?
Changes in temperature and rainfall shift the distribution of species towards the poles or higher altitude and alter development and life cycles. Seasonal events such as flowering, hatching and migration occur earlier, and species that depend on each other can become out of step.
Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026