What causes the climate to change, and what is the human role?
Explain the natural and human causes of climate change and describe how the enhanced greenhouse effect warms the planet
A clear, scaffolded answer to the N(A)-Level Geography outcome on the causes of climate change. The natural causes, the human causes, and how burning fossil fuels enhances the greenhouse effect and warms the planet.
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What this dot point is asking
This outcome asks you to explain what causes the climate to change, covering both natural causes and human causes, and to describe how the greenhouse effect works. The central idea is that the climate has always changed for natural reasons, but human activities are now adding extra greenhouse gases that strengthen the greenhouse effect and warm the planet faster than nature alone.
The answer
The natural greenhouse effect
The greenhouse effect is natural and necessary. Some gases in the atmosphere, called greenhouse gases (such as carbon dioxide, methane and water vapour), trap part of the heat that the Earth radiates back toward space. This keeps the planet warm enough to live on. Without the natural greenhouse effect, the Earth would be far too cold for life.
Natural causes of climate change
The climate changes naturally over long periods because of:
- Changes in the Sun's output: the amount of energy the Sun gives out varies slightly.
- Volcanic eruptions: large eruptions throw dust and gas into the air that can cool the planet for a few years.
- Natural cycles in the Earth's orbit that slowly change how much sunlight reaches us, causing ice ages over tens of thousands of years.
These explain past climate change but are too slow to explain the rapid recent warming.
Human causes of climate change
Human activities add extra greenhouse gases to the atmosphere:
- Burning fossil fuels (coal, oil and gas) for electricity, transport and industry releases large amounts of carbon dioxide.
- Deforestation removes trees that absorb carbon dioxide, and burning them releases even more.
- Farming, especially livestock and rice growing, releases methane.
The enhanced greenhouse effect
The extra greenhouse gases from human activity trap more heat than before, so the atmosphere warms beyond its natural level. This strengthening of the greenhouse effect is called the enhanced greenhouse effect, and it is the main reason for the rapid warming seen over the last century. Carbon dioxide levels have risen sharply since people began burning large amounts of fossil fuels.
Examples in context
Example 1. Rising carbon dioxide from fossil fuels. Since the industrial age, the burning of coal, oil and gas has pushed the amount of carbon dioxide in the atmosphere far above its natural level. Measurements show a steady rise, and because carbon dioxide traps heat, this build-up is the main human cause of warming, a key fact in data-response questions.
Example 2. Deforestation in Southeast Asia. Clearing and burning tropical forests in the region both releases stored carbon and removes the trees that would absorb carbon dioxide. This adds to the greenhouse gases in the atmosphere, showing how land-use change as well as fossil fuels drives climate change close to Singapore.
Try this
Q1. Name two greenhouse gases and a human activity that releases each. [2 marks]
- Cue. Carbon dioxide from burning fossil fuels; methane from farming (livestock and rice).
Q2. Explain why the natural greenhouse effect is important for life on Earth. [2 marks]
- Cue. Greenhouse gases trap some of the Earth's heat, keeping the planet warm enough to live on; without it the Earth would be far too cold.
Q3. Explain what is meant by the enhanced greenhouse effect. [2 marks]
- Cue. Humans add extra greenhouse gases that trap more heat than before, strengthening the greenhouse effect and warming the planet beyond its natural level.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain how human activities are causing the climate to warm.Show worked answer →
Human activities release greenhouse gases into the atmosphere. Burning fossil fuels (coal, oil and gas) for electricity, transport and industry releases large amounts of carbon dioxide. Cutting down forests (deforestation) removes trees that would absorb carbon dioxide and releases more when they are burned. Farming, especially livestock and rice, releases methane, another greenhouse gas.
These extra greenhouse gases trap more of the heat leaving the Earth, so the atmosphere warms. This is called the enhanced greenhouse effect.
What markers reward: naming human activities (burning fossil fuels, deforestation, farming) and the gases they release, and linking the extra greenhouse gases to trapping more heat (the enhanced greenhouse effect).
Original5 marksDescribe the natural greenhouse effect and explain how humans have made it stronger.Show worked answer →
The natural greenhouse effect is when greenhouse gases in the atmosphere, such as carbon dioxide and water vapour, trap some of the heat radiated from the Earth and keep the planet warm enough to live on. Without it, the Earth would be far too cold.
Humans have made it stronger by adding extra greenhouse gases, mainly carbon dioxide from burning fossil fuels and methane from farming. The extra gases trap more heat than before, so the planet warms beyond its natural level. This is the enhanced greenhouse effect.
What markers reward: the natural greenhouse effect described (gases trap heat, keeping Earth warm enough to live on), and humans adding extra gases to trap more heat (the enhanced effect).
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