Explain why it is difficult for scientists to predict the effects of increased greenhouse gas emissions on global climate change.

AQA GCSE Chemistry (8462) — 4.9.3 Common atmospheric pollutants and their sources · Explain · 4 marks · View as Markdown

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

Many scientists use computer models to predict how increasing levels of carbon dioxide and methane in the atmosphere will affect the Earth's climate. However, there is debate about the reliability of these predictions.

Model answer (4 marks)

The global climate is a very complex system, so it is difficult to model accurately.
Models have to be simplified and may only use part of the evidence.
This leads to speculation and opinions that may be biased.
Predictions are based on peer‑reviewed evidence but uncertainty remains; scientists are not certain that human activities alone cause the temperature increase.

Examiner tips

Use the exact terms from the mark scheme – ‘complex system’, ‘simplified’, ‘speculation’, ‘uncertainty’.
Show the logical flow: complexity → simplification → bias → uncertainty.
Keep each point brief – 1–2 sentences per mark.

Common mistakes

Using vague words like ‘hard’ or ‘difficult’ without linking to complexity.
Over‑explaining the science (e.g., detailed feedback loops) instead of summarising the four points.

Mark scheme (4 marks)

Global climate is a very complex system (so it is difficult to model accurately)
Models have to be simplified / models may only use part of the evidence
This leads to speculation and opinions that may be biased
Predictions are based on peer-reviewed evidence but uncertainty remains / scientists believe (not certain) human activities cause temperature increase

Key terms in this question

global climate change

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