Revision notes for AQA GCSE Chemistry Global climate change. Open the guide for explanations and worked examples. Written against the AQA GCSE Chemistry (8462) specification, so the content matches what's examinable rather than general Chemistry background.
Global climate change
What you'll learn
- Why an increase in average global temperature is a major cause of climate change.
- The difference between weather, climate, global warming and climate change.
- Four potential effects of global climate change that GCSE exam questions often ask for.
- How to discuss the scale, risk and environmental implications of climate change.
The starting point: greenhouse gases
You have already met carbon dioxide and methane as greenhouse gases. These gases absorb some of the infrared radiation given out by the Earth and re-radiate it, helping to keep the planet warm enough for life.
This natural warming is called the greenhouse effect. The problem is that human activities have increased the concentration of greenhouse gases in the atmosphere, causing an enhanced greenhouse effect.
Definition
Enhanced greenhouse effect
The enhanced greenhouse effect is the extra warming of the Earth caused by increased concentrations of greenhouse gases, such as carbon dioxide and methane, in the atmosphere.
Extra greenhouse gases mean more infrared radiation is absorbed and re-radiated back towards Earth’s surface. This increases the average global temperature.
Weather, climate, global warming and climate change
These terms are related, but they do not mean exactly the same thing.
Weather
Weather means the short-term conditions in one place, such as temperature, rainfall, wind and cloud cover over hours or days.
For example, “It rained heavily in Manchester yesterday” is about weather.
Climate
Climate means the long-term pattern of weather in a region, usually averaged over many years.
For example, “The UK has mild, wet winters compared with many countries at the same latitude” is about climate.
Definition
Climate change
Climate change is a long-term change in the usual patterns of climate, such as temperature, rainfall, wind patterns and frequency of extreme weather events.
Global warming
Global warming means the increase in the Earth’s average surface temperature.
Global warming is a major cause of current climate change, because changing temperature affects oceans, ice, rainfall patterns, wind patterns and ecosystems.
Key Idea
The main chain of ideas
More greenhouse gases → enhanced greenhouse effect → higher average global temperature → climate change.
Common Mistake
Weather is not climate
A single hot day does not prove climate change, and a single cold day does not disprove it. Climate change is about long-term trends and patterns, not one-off weather events.
Why average global temperature matters
The phrase average global temperature means the mean temperature of the Earth’s surface, calculated using measurements from many locations around the world.
It is important because Earth’s systems are connected. A small rise in the average temperature can still have large effects, because it changes:
- how much ice melts
- how much water evaporates from oceans and land
- how much energy is available in weather systems
- where plants and animals can survive
- how warm oceans become
Analogy
A small average change can still matter
If your body temperature rises by only a few degrees, that can be very serious. Similarly, a few degrees of global temperature change can strongly affect ice, oceans, weather and ecosystems.
Potential effect 1: melting ice and rising sea levels
As average global temperature increases, glaciers and ice sheets can melt more quickly. This adds water to the oceans.
Also, warmer water expands slightly. This is called thermal expansion, and it also contributes to sea level rise.
Definition
Sea level rise
Sea level rise is an increase in the average height of the ocean surface, caused mainly by melting land ice and expansion of warmer seawater.
Rising sea levels can lead to:
- flooding of low-lying coastal areas
- coastal erosion
- loss of habitats such as salt marshes
- increased risk to coastal towns, cities and farmland
Example
Explaining sea level rise
A student writes: “Global warming melts ice, so sea levels rise.”
Improve the answer by making the science more precise.
- Identify which ice matters most: melting land ice, such as glaciers and ice sheets, adds extra water to the oceans.
- Add the second process: as seawater warms, it expands, so the same mass of water takes up more volume.
- Link to the effect: both processes can increase sea level, raising the risk of coastal flooding and habitat loss.
Common Mistake
All melting ice does not affect sea level equally
Melting land ice increases sea level because water is added to the sea. Melting floating sea ice has a much smaller direct effect on sea level because it is already displacing seawater.
Potential effect 2: more extreme weather
A warmer atmosphere and warmer oceans can change weather patterns. This can increase the frequency or severity of some extreme weather events.
Definition
Extreme weather
Extreme weather means weather that is unusually severe or unusual for a particular place, such as heatwaves, droughts, intense storms or very heavy rainfall.
Possible examples include:
- more frequent heatwaves
- longer droughts in some regions
- more intense rainfall and flooding in other regions
- stronger storms in some areas
Be careful: climate change does not mean every place becomes hotter and drier all the time. It means long-term patterns shift, and the effects vary by region.
Tip
Use careful wording
In exams, write “may increase the frequency or severity of extreme weather” rather than “will cause storms everywhere”. Climate effects are often about increased risk, not identical outcomes in every location.
Potential effect 3: changes in rainfall and water supply
Climate change can affect the water cycle, which is the movement of water between oceans, the atmosphere, land and living organisms.
Warmer temperatures can increase evaporation. This can lead to more water vapour in the atmosphere, but rainfall may not be spread evenly. Some regions may get more intense rain, while others may experience less rainfall.
This can cause:
- droughts and water shortages
- reduced crop growth
- increased flooding after heavy rainfall
- changes to river flow and freshwater habitats
Example
Linking temperature change to drought risk
Explain how an increase in average global temperature could increase drought risk in some regions.
- Higher temperatures increase evaporation from soil, rivers, lakes and plants.
- If rainfall does not increase enough to replace this lost water, the land becomes drier over time.
- Drier soils and reduced river flow can lead to drought, affecting crops, wildlife and human water supplies.
Potential effect 4: changes to habitats and biodiversity
A habitat is the place where an organism lives. Biodiversity means the variety of living organisms in an area, including different species of plants, animals and microorganisms.
Climate change can alter habitats by changing temperature, rainfall, sea level and seasonal patterns.
Definition
Biodiversity
Biodiversity is the variety of living organisms in an ecosystem or on Earth as a whole.
As climate changes, some species may:
- move to cooler areas, such as further north or to higher altitudes
- breed or migrate at different times of year
- struggle to find food if seasonal timings change
- decline in number if they cannot adapt or move
- become extinct in extreme cases
For example, coral reefs are sensitive to warmer ocean temperatures. If conditions become unsuitable, coral ecosystems can be damaged, affecting many species that depend on them.
Key Idea
Ecosystems are connected
Climate change can affect one species directly, but it can also affect food webs, habitats and biodiversity because organisms depend on each other.
Discussing scale, risk and environmental implications
GCSE questions may ask you to discuss climate change rather than just list effects. That means you need to go beyond naming an effect.
A strong discussion often includes three ideas: scale, risk and environmental implications.
Scale
Scale means the size or level of the impact.
Climate change can operate on different scales:
- local: flooding in a particular town
- regional: drought affecting a whole farming region
- global: rising sea levels affecting coastlines worldwide
Scale can also mean time scale. Some impacts happen quickly, such as a heatwave. Others develop over decades, such as sea level rise.
Risk
Risk means the chance of something harmful happening, combined with how serious the harm would be.
For climate change, risk is not the same everywhere. A low-lying island may face a high risk from sea level rise. An inland area may face more risk from drought or heatwaves.
Environmental implications
Environmental implications are the effects on natural surroundings, ecosystems and living organisms.
Examples include:
- loss of coastal habitats due to flooding or erosion
- reduced biodiversity if species cannot adapt
- changes in food webs
- damage to freshwater ecosystems during drought
- increased wildfire risk in some dry regions
Example
Discussing a climate change impact
A question asks: “Discuss the possible environmental effects of rising global temperatures.”
- Choose a specific effect: rising temperatures can melt land ice and warm seawater, causing sea level rise.
- Add scale: this can affect coastlines in many parts of the world, but low-lying areas are especially vulnerable.
- Add risk: the risk is greater where large populations or important habitats are close to sea level.
- Add environmental implications: flooding and erosion can destroy coastal habitats and reduce biodiversity.
How to write about uncertainty
Climate change predictions use evidence from temperature records, ice cores, satellite data and computer models. Models are useful, but the exact effects are difficult to predict because Earth’s climate system is complex.
This does not mean scientists know nothing. It means predictions often come with ranges and probabilities.
Common Mistake
Uncertainty does not mean no evidence
Scientific uncertainty usually means “we cannot predict the exact size, timing or location of every effect”, not “climate change is just a guess”.
Good GCSE answers use cautious scientific language:
- “could lead to…”
- “may increase the risk of…”
- “is likely to cause…”
- “in some regions…”
Bringing the four effects together
For this specification, you should be able to briefly describe four potential effects of global climate change. A solid set to remember is:
- Sea level rise due to melting land ice and thermal expansion of seawater.
- More extreme weather, such as heatwaves, droughts, storms and heavy rainfall.
- Changes in rainfall and water supply, causing droughts in some areas and flooding in others.
- Changes to habitats and biodiversity, as species move, decline or become extinct.
Tip
Four-effect memory hook
Remember SEHR: Sea levels, Extreme weather, Habitats, Rainfall. If you can explain each one, you are well prepared for this topic.
Exam technique
In the exam
- If asked for effects, give descriptions, not just single words: “sea levels rise, causing coastal flooding” is stronger than “flooding”.
- If asked to discuss, include scale, risk and at least one environmental implication, such as habitat loss or reduced biodiversity.
- Use cautious wording like “may”, “could” and “in some regions” when describing climate impacts, because effects vary around the world.
Self review
Check yourself
- What is the difference between weather and climate?
- Describe four potential effects of global climate change.
- Why can a small increase in average global temperature have large environmental effects?
Carbon dioxide and methane as greenhouse gases
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