AQA GCSE Chemistry 4.9.2 Carbon Dioxide and Methane as Greenhouse Gases Exam Questions

About AQA GCSE Chemistry 4.9.2 Carbon Dioxide and Methane as Greenhouse Gases

AQA GCSE Chemistry 4.9.2 explains how greenhouse gases keep the Earth warm enough for life, and how human activities are increasing their amounts. You learn which gases are greenhouse gases, how they absorb and re-emit long wavelength radiation, the evidence for climate change, its possible effects, and how a carbon footprint can be reduced. It is assessed on Paper 2 and links to combustion of fuels in 4.7.1 and pollutants in 4.9.3. Examiners like questions that ask you to evaluate data, discuss uncertainty in climate models and peer review, and suggest realistic actions with their problems.

What you need to know

• Greenhouse gases Water vapour, carbon dioxide and methane are greenhouse gases. They maintain temperatures on Earth high enough to support life.
• The greenhouse effect Short wavelength radiation from the Sun passes through the atmosphere and is absorbed by the Earth's surface. The Earth emits long wavelength (infrared) radiation, which is absorbed by greenhouse gases and re-radiated, warming the atmosphere.
• Human activities Burning fossil fuels and deforestation increase carbon dioxide. Livestock farming (cattle), rice paddy fields and landfill sites increase methane.
• Evidence and uncertainty Most scientists agree, based on peer-reviewed evidence, that human activities will cause the mean global temperature to rise. Climate models are complex and simplified, which leads to some uncertainty and speculation in the media.
• Effects of climate change Rising sea levels causing flooding and coastal erosion; more frequent and severe storms; changes in the amount, timing and distribution of rainfall; temperature and water stress; changes in food production and the distribution of wildlife.
• Carbon footprint The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event. It can be reduced by using renewable energy, energy conservation, carbon capture and storage, carbon taxes and carbon off-setting such as planting trees. Problems include scientific disagreement, lifestyle change and economic factors.

Common mistakes in 4.9.2 Carbon Dioxide and Methane as Greenhouse Gases

• Confusing the greenhouse effect with the hole in the ozone layer. They are different problems.
• Saying greenhouse gases 'trap' or 'reflect' heat. They absorb long wavelength infrared radiation and re-emit it.
• Saying all of the Sun's radiation is absorbed by greenhouse gases. Short wavelength radiation passes through; it is the long wavelength radiation emitted by the Earth that is absorbed.
• Calling the greenhouse effect itself bad. Without it the Earth would be too cold for life; the problem is an enhanced greenhouse effect.
• Listing 'global warming' as an effect of climate change. Give specific effects such as sea level rise or changes to rainfall.

Try three 4.9.2 Carbon Dioxide and Methane as Greenhouse Gases exam-style questions