DP Biology (first assessment 2025)

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Question 22N.2.SL.TZ0.3b

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Date November 2022 Marks available [Maximum mark: 3] Reference code 22N.2.SL.TZ0.3b
Level SL Paper 2 Time zone TZ0
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 3]
22N.2.SL.TZ0.3b
(b)

Explain how increased levels of atmospheric carbon dioxide contribute to global warming.

[3]

Markscheme
  1. carbon dioxide absorbs/traps long wavelength/infra-red radiation;
  2. more heat trapped in/less heat escapes from atmosphere with more carbon dioxide;
  3. short wave/UV radiation from the sun passes through the atmosphere/reaches the Earth’s surface;
  4. radiation from the sun/sunlight warms the (surface of the) Earth;
  5. long wavelength/infra-red radiated from the (warmed) Earth’s surface;

Do not accept answers relating to ozone in the atmosphere because the question refers to carbon dioxide.
For mpa do not accept heat instead of LW/IR radiation.

Examiners report

Understanding of the greenhouse effect is very patchy and in some cases is lamentably weak. Some candidates still think that 'increased CO2 burns a hole through the ozone layer' or that the greenhouse effect is due to carbon dioxide being reflected back to the Earth's atmosphere. Nearly all answers included errors of understanding. Global warming will have a major impacts on all IB students' future lives so we owe it to them to make sure they understand how it is happening. Perhaps they should memorise these elements:

  • Short wave radiation from the sun causes the Earth's surface to warm up. 
  • The warmed surface of the Earth emits long wave radiation.
  • Greenhouse gases such as carbon dioxide absorb some of this long-wave radiation, which becomes
    heat.
  • If the concentration of carbon dioxide or other greenhouse gases in the atmosphere rises, more heat is
    trapped and the Earth becomes warmer.
  • Burning of fossil fuels causes the atmospheric carbon dioxide concentration to rise.

Syllabus sections