Carbon dioxide is a greenhouse gas. Explain how an increase in carbon dioxide levels in the atmosphere leads to climate change and describe two possible effects of climate change on living organisms.

Pearson Edexcel A-Level Biology A (9BI0) — 3.3 Climate change · Explain and Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Levels of carbon dioxide in Earth's atmosphere have been rising since the Industrial Revolution, largely due to the burning of fossil fuels and deforestation. Scientists have recorded a correlation between rising carbon dioxide concentrations and rising mean global temperatures.

Model answer (5 marks)

Carbon dioxide is a greenhouse gas that absorbs infrared radiation emitted by the Earth’s surface. The absorbed energy is re‑radiated in all directions, but a significant portion is trapped in the atmosphere, reducing the rate at which heat escapes to space. This additional heat causes mean global temperatures to rise, producing global warming.

Two possible effects of climate change on living organisms are:
1. Species may shift their distribution or range to cooler regions, such as moving poleward or to higher altitudes, because their original habitat becomes too warm.
2. Some species may face extinction if they cannot adapt or migrate, as their habitats and food sources disappear.

Rising temperatures can also disrupt interspecific relationships (e.g. predator–prey, pollinator–plant) because different species respond to warming at different rates, leading to changes in biodiversity and ecosystem function.

Examiner tips

  • Use the term "greenhouse gas" and mention infrared radiation; link trapping of heat to global warming. Include two specific, named effects (range shift, extinction) and explain the link to temperature. Show the causal chain: CO₂ ↑ → heat trapping ↑ → temperature ↑ → ecological impacts.
  • common_mistakes
  • :
  • Failing to mention infrared radiation or heat trapping. Giving vague effects such as “more heat” instead of specific ecological consequences. Mixing up cause and effect or omitting the link between temperature rise and biodiversity changes.

Mark scheme (5 marks)

  1. Carbon dioxide (and other greenhouse gases) trap/absorb heat (infrared radiation) in the atmosphere
  2. This causes mean global temperatures to rise / global warming
  3. Effect 1 on living organisms — named valid effect, e.g. species / organisms may shift their distribution / range to cooler regions (poles or higher altitudes) as their original habitat becomes too warm
  4. Effect 2 on living organisms — named valid effect, e.g. some species may face extinction if they cannot adapt or migrate as habitats/food sources are lost
  5. Qualitative link made between rising temperatures and change in biodiversity / ecosystems, e.g. as temperatures rise, interspecific relationships (e.g. predator–prey, pollinator–plant) may become disrupted because species respond to warming at different rates

Key terms in this question

greenhouse gas · carbon dioxide · climate change

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