What's Causing Climate Change? Revision Notes | GCSE AQA Higher Geography

1. Why Climate Change Matters for Your Exam

The climate has always changed — but the rate of change happening right now is unlike anything in recorded human history. Your exam will ask you to explain why that is, and the answer involves two very different sets of causes: natural ones that have operated for millions of years, and human ones that have accelerated sharply since the Industrial Revolution.

AQA wants you to be precise: name the factor, explain the mechanism, and link it to a climate outcome. This lesson builds that chain of reasoning for every factor on the specification.

2. Natural Factors Driving Climate Change

Before humans ever burned coal, Earth's climate swung between ice ages and warm periods. Three natural mechanisms explain those swings: changes in Earth's orbit, volcanic activity, and variations in solar output.

Picture Earth's orbit as a slightly squashed circle. When the orbit becomes more elliptical, Earth spends part of the year much further from the Sun, receiving less energy and cooling down. When the axis tilts more steeply, summers get hotter and winters colder. These cycles operate over 20,000–100,000 years, so they cannot explain the rapid warming seen over the last 150 years — but they are the dominant driver of natural ice-age cycles.

Volcanic activity is a second natural driver. Large eruptions blast sulphur dioxide ($SO_2$) into the stratosphere, where it forms tiny droplets of sulphuric acid that reflect incoming solar radiation back into space. The result is short-term global cooling — the 1991 eruption of Mount Pinatubo in the Philippines lowered global average temperatures by around 0.5°C for roughly two years. Over geological timescales, however, sustained volcanic activity also releases large volumes of $CO_2$, contributing to longer-term warming.

Solar output — the amount of energy the Sun radiates — is not perfectly constant. Sunspot cycles (roughly 11 years) and longer-term variations in solar luminosity mean Earth receives slightly more or less energy at different times. Scientists measure this as total solar irradiance. Periods of reduced solar activity, such as the Maunder Minimum (approximately 1645–1715), coincided with the 'Little Ice Age' in Europe, suggesting a real link between solar output and surface temperatures.

All three natural factors are real and measurable — but crucially, scientists have modelled what current temperatures should be if only natural factors were operating. The observed warming since the mid-20th century far exceeds those natural predictions. That gap is where human factors come in.

3. Human Factors Driving Climate Change

Human activity has added greenhouse gases to the atmosphere at a rate that natural systems cannot absorb. The three main human factors the specification requires you to know are the burning of fossil fuels, agriculture, and deforestation.

Burning fossil fuels — coal, oil, and natural gas — releases $CO_2$ that was locked underground for millions of years. Power stations, vehicles, and industry are the largest sources. Atmospheric $CO_2$ concentration has risen from around 280 parts per million (ppm) before industrialisation to over 420 ppm today — a level not seen for at least 800,000 years according to ice-core records.

Agriculture contributes through two main pathways. Livestock farming — particularly cattle — produces methane ($CH_4$) during digestion (a process called enteric fermentation). Rice paddies also release methane as organic matter decomposes in flooded, low-oxygen conditions. Methane is a far more potent greenhouse gas than $CO_2$ over a 20-year period, making livestock farming a significant driver of warming even though total methane emissions are smaller in volume than $CO_2$ emissions.

Deforestation removes trees that would otherwise absorb $CO_2$ through photosynthesis. When forests are cleared — particularly tropical rainforests such as the Amazon — two things happen simultaneously: the carbon stored in the trees is released (often through burning), and the ongoing carbon sink is destroyed. This double effect makes deforestation one of the most significant human contributions to rising greenhouse gas concentrations.

4. Comparing Natural and Human Causes

Now that you know both sets of causes, the exam will often ask you to compare them. The key distinction is timescale and rate. Natural factors operate over thousands to millions of years; the current warming trend has accelerated over just 150 years — far too fast to be explained by orbital cycles or gradual solar changes alone.

Scientific consensus — supported by organisations such as the IPCC (Intergovernmental Panel on Climate Change) — is that human factors are the dominant cause of the warming observed since the mid-20th century. Natural factors are still operating, but they cannot account for the speed or magnitude of recent temperature rises on their own.

5. Effects of Climate Change

Climate change — whether driven by natural or human factors — produces a range of effects across physical and human systems. The specification states you need to know that climate change has a range of effects, so be ready to describe and explain them.

• Rising global average temperatures — increasing frequency and intensity of heatwaves
• Melting ice sheets and glaciers — contributing to sea-level rise
• Rising sea levels — increased coastal flooding and erosion, threatening low-lying areas
• More extreme weather events — stronger storms, prolonged droughts, and heavier rainfall events
• Ecosystem disruption — species migration, coral bleaching, and biodiversity loss
• Threats to food and water security — changing rainfall patterns affecting agriculture

These effects are interconnected. Melting Arctic sea ice reduces the albedo (reflectivity) of Earth's surface — dark ocean water absorbs more solar energy than white ice, creating a positive feedback loop that accelerates warming further. This kind of feedback is why scientists describe climate change as a self-reinforcing system once certain thresholds are crossed.

6. Exam Technique: Getting Full Marks on Climate Change Questions

Climate change questions appear regularly on AQA Paper 1. The command words vary, so your answer structure must adapt. Here is how to handle the most common question types on this topic.

Worked example: Answering an 'Explain' Question on Human Causes of Climate Change

Explain how the burning of fossil fuels contributes to climate change. [4 marks]

1. Burning fossil fuels releases carbon dioxide ($CO_2$) into the atmosphere. — [B1] — name the gas and the source. Do not just say 'pollution' — be specific.
2. $CO_2$ is a greenhouse gas. It absorbs outgoing infrared radiation from Earth's surface and re-emits it back downwards. — [B1] — this is the mechanism. Many students skip this step and lose the mark.
3. This traps more heat in the lower atmosphere, raising global average temperatures — the enhanced greenhouse effect. — [B1] — use the term 'enhanced greenhouse effect' for the extra mark.
4. Atmospheric $CO_2$ has risen from approximately 280 ppm before industrialisation to over 420 ppm today, correlating with a rise in global average temperature of around 1.1°C. — [B1] — a specific statistic or piece of evidence lifts a 3-mark answer to 4 marks.

Answer: Burning fossil fuels releases $CO_2$, a greenhouse gas that absorbs and re-emits infrared radiation, trapping heat in the atmosphere (enhanced greenhouse effect). $CO_2$ levels have risen from ~280 ppm to over 420 ppm since industrialisation, driving a global temperature rise of approximately 1.1°C.

For 'compare' questions, you must address both similarities and differences — and use connective language such as 'whereas', 'in contrast', or 'both'. A common trap is writing two separate descriptions without ever making a direct comparison.

Climate change is the result of both natural and human factors working together — but the evidence is clear that human activity has dramatically accelerated the rate of change since industrialisation, producing effects that now affect ecosystems, sea levels, and weather patterns across the globe.