C24: Climate Change and Pollution
Greenhouse gases, climate change and air pollution
📋 Greenhouse Gases and Human Activities
Human activities are increasing the concentration of greenhouse gases in the atmosphere. The main greenhouse gases are carbon dioxide (CO₂) and methane (CH₄). Water vapour is also a greenhouse gas.
| Greenhouse Gas | Sources (Human Activities) |
|---|---|
| Carbon dioxide (CO₂) | Burning fossil fuels (coal, oil, gas) for energy and transport; deforestation (trees that absorbed CO₂ are removed) |
| Methane (CH₄) | Farming (cattle and rice paddies produce methane); landfill sites (decomposition of organic waste); extraction of fossil fuels |
📝 Climate Change
Increased greenhouse gas concentrations are causing global warming — an increase in the average temperature of the Earth. This leads to climate change, with significant consequences.
| Consequence | Explanation |
|---|---|
| Rising sea levels | Thermal expansion of oceans and melting of ice caps and glaciers |
| Changing weather patterns | More extreme weather events (floods, droughts, hurricanes) |
| Habitat loss | Ecosystems change faster than species can adapt (e.g. coral bleaching, Arctic ice loss) |
| Species migration and extinction | Species move to cooler areas; those that cannot adapt or migrate may die out |
| Impact on food production | Changing rainfall and temperature affect crop yields |
📝 Carbon Footprint
A carbon footprint is the total amount of CO₂ and other greenhouse gas emissions caused by a person, organisation, event or product, expressed as a CO₂ equivalent.
- It includes direct emissions (e.g. from driving a car) and indirect emissions (e.g. from manufacturing the products you buy).
- Everything we do that uses energy from fossil fuels contributes to our carbon footprint.
📝 Reducing Carbon Footprints
Reducing carbon footprints involves reducing greenhouse gas emissions. Methods include using renewable energy, improving energy efficiency, carbon capture, and changing agricultural practices.
- Replace fossil fuels with renewable energy sources (wind, solar, hydroelectric, geothermal).
- Improve insulation and energy efficiency in homes and industry.
- Use carbon capture and storage (CCS) — capture CO₂ from power stations and store it underground.
- Reduce deforestation and plant more trees (afforestation) to absorb CO₂.
- Reduce consumption of meat and dairy (less methane from farming).
- Use more public transport, electric vehicles, and cycling.
Difficulties in reducing carbon footprints: scientific disagreement over causes and effects, economic considerations (fossil fuels are cheap and established), lack of political will, incomplete international cooperation, and reluctance of individuals to change lifestyle.
📝 Air Pollution
Burning fossil fuels also releases pollutants that harm the environment and human health: sulfur dioxide, oxides of nitrogen, and particulates (carbon particles/soot).
| Pollutant | Source | Environmental Problem | Health Problem |
|---|---|---|---|
| Sulfur dioxide (SO₂) | Burning sulfur-containing fossil fuels | Acid rain (damages buildings, ecosystems) | Respiratory irritation |
| Oxides of nitrogen (NOₓ) | High-temperature combustion in engines | Acid rain, photochemical smog | Respiratory problems |
| Particulates (soot) | Incomplete combustion of fossil fuels | Global dimming | Respiratory problems (asthma, lung disease) |
| Carbon monoxide (CO) | Incomplete combustion of fossil fuels | Toxic — binds to haemoglobin, reduces oxygen in blood | Fatal in high concentrations |
❓ Practice Questions
Q1: Name two greenhouse gases increased by human activity and state one source of each.
Q2: Describe three consequences of global warming / climate change.
Q3: Define the term "carbon footprint" and suggest two ways an individual could reduce their carbon footprint.
Q4: Higher Explain how sulfur dioxide and oxides of nitrogen cause acid rain. Describe two effects of acid rain on the environment.
Q5: Explain what particulates are, how they are produced, and two problems they cause.
✅ Answers
- CO₂ — burning fossil fuels / deforestation. Methane — farming (cattle) / landfill sites.
- (1) Rising sea levels due to thermal expansion and melting ice. (2) More extreme weather — floods, droughts, storms. (3) Habitat loss and species extinction — ecosystems change too quickly for species to adapt.
- A carbon footprint is the total amount of CO₂ and other greenhouse gas emissions caused by a person, organisation or product. Two ways to reduce: use public transport, walk or cycle instead of driving; use renewable energy sources at home.
- SO₂ from burning sulfur-containing fossil fuels and NOₓ from high-temperature combustion dissolve in moisture in the atmosphere to form sulfuric acid and nitric acid. These fall as acid rain. Effects: (1) Corrodes buildings and statues. (2) Makes lakes and soil acidic, killing fish and trees.
- Particulates are tiny solid particles (soot/carbon) produced by incomplete combustion. Problems: (1) Respiratory problems such as asthma. (2) Global dimming by reflecting sunlight back into space.
🎯 Exam Tips
- When asked about climate change consequences, be specific — mention sea level rise, extreme weather, habitat loss, species extinction, and food production impacts
- For pollution questions, always link the pollutant to its source AND its effect (SO₂ → acid rain → corrodes buildings/kills aquatic life)
- Global dimming is caused by particulates reflecting sunlight, NOT by greenhouse gases
- Carbon footprint includes DIRECT and INDIRECT emissions
- When asked why reducing carbon footprints is difficult, give specific reasons: economic, political, social
🔢 Maths Skills
Mathematical Skills
You need to interpret data on atmospheric CO₂ concentrations over time, calculate percentage changes in greenhouse gas levels, and compare carbon footprints of different activities.
Maths Example
Atmospheric CO₂ was 280 ppm in 1750 and 420 ppm in 2024. Calculate the percentage increase.
Percentage increase = ((420 − 280) ÷ 280) × 100 = (140 ÷ 280) × 100 = 50%
Maths Example 2
A car journey of 100 miles produces 22 kg CO₂. A train journey of the same distance produces 6 kg CO₂. What percentage reduction in CO₂ is achieved by taking the train?
Reduction = 22 − 6 = 16 kg. Percentage reduction = (16 ÷ 22) × 100 = 72.7%
⚠️ Common Misconceptions
Watch Out!
1. Wrong: The greenhouse effect is caused by human pollution Correct: The greenhouse effect is NATURAL and keeps Earth warm enough for life — human activities are ENHANCING it, causing additional warming
2. Wrong: Global dimming is caused by greenhouse gases Correct: Global dimming is caused by PARTICULATES (tiny solid particles from incomplete combustion) reflecting sunlight — it is NOT related to greenhouse gases
3. Wrong: Carbon monoxide causes acid rain Correct: Carbon monoxide is toxic (binds to haemoglobin) but does NOT cause acid rain — acid rain is caused by SO₂ and NOₓ
4. Wrong: Reducing carbon footprint means stopping all energy use Correct: Reducing carbon footprint means switching to low-carbon alternatives (renewable energy, electric vehicles, insulation) — not stopping energy use entirely
✍️ 6-Mark Question
Extended Answer
6 marks: Explain how human activities are increasing greenhouse gas concentrations, describe three consequences of climate change, and suggest why it is difficult to reduce global emissions.
Human activities are increasing greenhouse gas concentrations in several ways. Burning fossil fuels (coal, oil, natural gas) for electricity, heating and transport releases large amounts of CO₂ that was previously locked underground. Deforestation reduces the number of trees available to absorb CO₂ through photosynthesis, and when trees are burned or decompose they release stored carbon as CO₂. Farming produces methane from cattle digestion and rice paddies, while landfill sites produce methane from anaerobic decomposition of organic waste. Three consequences of climate change: rising sea levels (thermal expansion of oceans and melting ice caps), more extreme weather events (droughts, floods, storms), and habitat loss and species extinction (ecosystems change too rapidly for species to adapt). It is difficult to reduce global emissions because: fossil fuels are cheap and well-established as energy sources, making alternatives expensive; there is a lack of international cooperation — not all countries agree on targets or implement them fully; and individuals are reluctant to change their lifestyles (e.g. reduce car use, eat less meat). Economic growth in developing countries also increases energy demand.
Mark scheme: 1 mark for burning fossil fuels increasing CO₂; 1 mark for deforestation increasing CO₂; 1 mark for farming/landfill increasing methane; 1 mark for three consequences; 1 mark for difficulty — economic factors; 1 mark for difficulty — international cooperation or lifestyle reluctance
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
Two power stations each generate 1000 MW of electricity:
- Coal-fired: emits 900,000 tonnes CO₂ per year, 5,000 tonnes SO₂ per year
- Natural gas: emits 400,000 tonnes CO₂ per year, 10 tonnes SO₂ per year
(a) Calculate the percentage reduction in CO₂ emissions when switching from coal to gas.
(b) Explain why switching from coal to natural gas also reduces acid rain.
(c) A politician claims that "switching to gas solves the climate change problem." Evaluate this claim.
Answers: (a) Reduction = 900,000 − 400,000 = 500,000 tonnes. Percentage reduction = (500,000 ÷ 900,000) × 100 = 55.6%. (b) Coal contains sulfur impurities which form SO₂ when burned. Natural gas is mostly methane (CH₄) with virtually no sulfur, so far less SO₂ is produced. Since SO₂ causes acid rain, switching to gas greatly reduces acid rain. (c) While switching to gas reduces CO₂ by about 56%, the gas power station still emits 400,000 tonnes of CO₂ per year — a very significant amount. Gas is still a fossil fuel, so it still contributes to climate change. To truly address climate change, we need to switch to renewable energy sources (wind, solar, nuclear) that produce zero CO₂, not just to a less-polluting fossil fuel. The politician's claim is an overstatement — gas is better than coal but is not a solution on its own.
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