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Greenhouse Gases and Climate ChangeAQA GCSE Chemistry: Revision notes

Section 1

What Causes the Greenhouse Effect?

The greenhouse effect describes how certain gases in the atmosphere keep the Earth warm enough to support life. The main greenhouse gases are:

  • Water vapour
  • Carbon dioxide
  • Methane

These gases absorb long wavelength radiation re-emitted from the Earth's surface and re-emit it in all directions, including back towards the Earth. This traps energy near the surface and maintains the temperatures needed to support life, in terms of the interaction between short and long wavelength radiation and matter.

Key termsgreenhouse effectgreenhouse gases
Think of it like this

Greenhouse gases act like a blanket around the Earth, letting short wavelength radiation in but slowing down the escape of long wavelength radiation back out to space.

Section 2

How Do Human Activities Increase Greenhouse Gases?

Human activities increase the amounts of greenhouse gases in the atmosphere. You should be able to recall at least two human activities that increase each of the following:

  • Carbon dioxide — for example, burning fossil fuels and deforestation
  • Methane — for example, livestock farming and rice paddy fields

As these gases build up, more long wavelength radiation is trapped, enhancing the greenhouse effect.

Exam tip

Learn at least two named human causes for each gas — carbon dioxide and methane — as exam questions often ask for two examples.

Section 3

What Is Global Climate Change?

An increase in average global temperature is considered a major cause of global climate change. Potential effects of global climate change include:

  1. Rising sea levels (from melting ice and thermal expansion of water)
  2. Changing amounts, timings and distributions of rainfall
  3. More frequent or more severe extreme weather events
  4. Changes to the distribution of wildlife species

These effects carry real scale, risk and environmental implications that scientists continue to study.

Key termsglobal climate change

Section 4

How Should We Evaluate Climate Change Evidence?

When evaluating reports on global climate change, it's important to look critically at the quality of evidence:

  • Consider uncertainties in the evidence base — measurements and models are never perfectly precise
  • Recognise the importance of peer review, where other scientists check results before they are published
  • Recognise the importance of communicating results clearly to a wide range of audiences, including non-scientists and policymakers

Good scientific practice means being open about the limits of the evidence, not just the conclusions.

Key termspeer review
Common mistake

Don't just describe climate change effects when asked to 'evaluate evidence' — you need to comment on data quality, uncertainty and peer review.

Must Know

  • The greenhouse effect is caused mainly by water vapour, carbon dioxide and methane absorbing and re-emitting long wavelength radiation
  • Human activities (e.g. burning fossil fuels, deforestation, livestock farming) increase carbon dioxide and methane in the atmosphere
  • Global climate change is linked to a rise in average global temperature, with effects including rising sea levels, changing rainfall and extreme weather
  • Evaluating climate change evidence means considering uncertainty, peer review, and clear communication to different audiences
  • Learn at least two human causes for increases in carbon dioxide and two for methane

That's the notes covered.

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