GeographyICSE Class 10 · Waste Management

Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution (ICSE Class 10)

Updated 17 October 2026 · Draft, not yet fact-checked

Global warming is the gradual rise in the earth's average surface temperature caused by greenhouse gases that trap heat. Acid rain is rain containing sulphuric and nitric acids formed from sulphur dioxide and nitrogen oxides. Eutrophication is the excess enrichment of water with nutrients, causing algal bloom and oxygen loss. Biomagnification is the increase of a non-biodegradable toxin along a food chain. Thermal pollution is the release of heated water that lowers dissolved oxygen and harms aquatic life.

Match each pollution type on the left with its main effect on the right, and recall its cause from the chapter notes.

Illustration drawn for QuestionBuddy.

Understand Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution

1. Global warming.

*Meaning:* the gradual rise in the average temperature of the earth's surface and lower atmosphere.
*Cause:* increased amounts of greenhouse gases such as carbon dioxide and methane, which trap heat.
*How waste adds to it:* burning fossil fuels and waste, deforestation, and methane from rotting waste in dumps.
*Effects:* melting glaciers, rising sea levels and extreme weather.

2. Acid rain.

*Meaning:* rain containing sulphuric and nitric acids.
*Cause:* sulphur dioxide and nitrogen oxides from burning coal, oil and waste combine with water vapour in the air.
*Effects:* damages buildings and monuments (for example marble), harms crops and forests, and makes lakes and soils acidic.

3. Eutrophication.

*Meaning:* the excessive enrichment of a lake or pond with nutrients (nitrates and phosphates).
*Sources:* fertiliser run-off, sewage and detergents.
*Process:* algae grow rapidly (algal bloom); when they die and decompose, bacteria use up the dissolved oxygen, so fish and other aquatic life die.

4. Biomagnification.

*Meaning:* the increase in the concentration of a non-biodegradable toxic substance (such as DDT, mercury or lead) at each higher level of a food chain.
*Process:* small amounts in water become larger in plankton, more in fish, and highest in birds or humans that eat the fish.
*Why it matters:* the toxin is not broken down or excreted, so it builds up in top consumers.

5. Thermal pollution.

*Meaning:* the release of heated water from power plants and industries into rivers, lakes or the sea.
*Effect:* the warm water holds less dissolved oxygen and harms fish and other aquatic organisms.

6. Linking the terms to waste. Rotting waste releases methane (global warming); burning waste releases sulphur and nitrogen oxides (acid rain); sewage and detergents add nutrients to water (eutrophication); non-biodegradable toxins in waste enter food chains (biomagnification); industries discharge hot water (thermal pollution).

7. How to write a definition. Give the meaning, the cause and one effect. Examiners reward the exact scientific term (for example 'dissolved oxygen' or 'greenhouse gases') and not just 'pollution'.

Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution: key facts

Global warming: Rise in average temperature
Greenhouse gases: carbon dioxide, methane
Effects: glaciers melt, sea level rises, extreme weather
Acid rain: Sulphuric and nitric acids
From sulphur dioxide and nitrogen oxides
Damages marble monuments, crops, lakes
Eutrophication: Nitrates and phosphates
Fertiliser run-off, sewage, detergents
Algal bloom
Oxygen used up
Fish die
Biomagnification: Non-biodegradable toxin (DDT, mercury, lead)
Concentration rises at each food-chain level
Highest in top consumers
Thermal pollution: Heated water from power plants and industries
Less dissolved oxygen
Harms aquatic life

How to answer Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution questions

For each term, write the meaning, the cause and the effect.

1Write a one-line definition using the key scientific words.
2Name the cause: for global warming, greenhouse gases; for acid rain, sulphur and nitrogen oxides; for eutrophication, nutrients; for biomagnification, a persistent toxin; for thermal pollution, hot water.
3State at least one effect, linked to the cause.
4For process terms (eutrophication, biomagnification), write the steps in order.
5For comparison questions, use the same headings for both terms.

Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A pond turns green

Suppose a pond near a farm turns green and smelly after the farmer applies a large quantity of fertiliser before a heavy shower, and fish begin to die a few days later.

Name the process and explain it in three steps.

Try it first, then show the solutionSolution

Fertiliser run-off adds nitrates and phosphates to the pond.
Algae grow rapidly and form a bloom; when they die, bacteria decomposing them use up the dissolved oxygen.
With little oxygen left, fish and other aquatic life die.

Answer: Eutrophication.

Memory hook: Nutrients in, algae bloom, oxygen out, fish die.

Toxin up the chain

Suppose a lake contains a very small, constant amount of a toxic non-biodegradable chemical. Plankton take it up, small fish eat plankton, and a bird eats many fish.

Where will the toxin be most concentrated, and what is the process called?

Try it first, then show the solutionSolution

Concentration rises at each higher level of the food chain.
So it is highest in the bird at the top, and the process is biomagnification.

Answer: In the bird; biomagnification.

Memory hook: Higher on the chain, higher the dose.

Tricks to remember Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution

Short memory aids. Say each one aloud once, then use it on a question the same day.

GAEBT
Global warming, Acid rain, Eutrophication, Biomagnification, Thermal pollution: the five terms in syllabus order.
Use it when: Recalling the list.
Fertiliser, bloom, no oxygen
Eutrophication: nutrients, algal bloom, oxygen used up, fish die.
Use it when: Writing the process.
S and N make acid
Sulphur dioxide and nitrogen oxides give sulphuric and nitric acids in acid rain.
Use it when: Cause of acid rain.

Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Define the term · 2 marks · Short answerBoard level

Define (a) global warming and (b) thermal pollution.

Try it first, then show the solutionSolution

(a) The gradual rise in the average temperature of the earth's surface and lower atmosphere caused by increased greenhouse gases that trap heat.
(b) The release of heated water from power plants and industries into rivers, lakes or the sea, which harms aquatic life.

Answer: (a) Rise in average temperature due to greenhouse gases (b) Release of hot water into water bodies.

Example 2: Causes and effect of acid rain · 3 marks · Short answerBoard level

State the gases responsible for acid rain and one effect each on buildings and on lakes.

Try it first, then show the solutionSolution

Sulphur dioxide and nitrogen oxides, from burning coal, oil and waste, combine with water vapour to form sulphuric and nitric acids.
Buildings: damage to buildings and monuments, for example marble.
Lakes: lakes and soils become acidic.

Answer: Sulphur dioxide and nitrogen oxides; it damages monuments and acidifies lakes.

Example 3: Eutrophication in steps · 4 marks · Short answerHarder board level

Explain how fertilisers can lead to the death of fish in a lake.

Try it first, then show the solutionSolution

Run-off from fields carries nitrates and phosphates into the lake.
Algae multiply rapidly (algal bloom).
When the algae die and decompose, bacteria use up the dissolved oxygen.
The fish and other aquatic life die for lack of oxygen.

Answer: Nutrients cause algal bloom; decomposition uses up oxygen; fish die.

Example 4: Biomagnification contrasted with eutrophication · 4 marks · Short answerHarder board level

Distinguish between eutrophication and biomagnification on (a) the substance involved, (b) the place where the effect is seen, (c) the final result.

Try it first, then show the solutionSolution

(a) Eutrophication involves nutrients (nitrates and phosphates); biomagnification involves a non-biodegradable toxin such as DDT, mercury or lead.
(b) Eutrophication occurs in a lake or pond; biomagnification builds up along a food chain.
(c) Eutrophication ends in oxygen loss and death of aquatic life; biomagnification ends with the highest concentration of the toxin in top consumers.

Answer: Nutrients in a water body leading to oxygen loss, versus a toxin concentrating up a food chain.

Example 5: Case study: a power plant by a river · 5 marks · Case-basedHOTS / competency

A power plant discharges hot water into a river and its coal-fired boilers emit sulphur dioxide. Downstream, the fish population falls and a nearby marble monument shows damage. (a) Name the two pollution problems. (b) Explain the fish decline. (c) Explain the monument damage. (d) Link the coal burning to global warming.

Try it first, then show the solutionSolution

(a) Thermal pollution and acid rain.
(b) Warm water holds less dissolved oxygen, which harms the fish.
(c) Sulphur dioxide forms sulphuric acid in rain, which damages marble.
(d) Burning coal releases carbon dioxide, a greenhouse gas that traps heat.

Answer: (a) Thermal pollution and acid rain (b) Less dissolved oxygen (c) Sulphuric acid attacks marble (d) Carbon dioxide traps heat.

Where students lose marks in Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution

The slips examiners see most often, and what to write instead.

Mistake: Defining global warming as 'pollution of air'
The scientific idea of rising average temperature is missing.
Do this: Write rise in average temperature due to greenhouse gases.
Usually costs: 1 mark.
Mistake: Forgetting dissolved oxygen in eutrophication
Only 'fish die' is written.
Do this: Write that bacteria use up the dissolved oxygen.
Usually costs: 1 mark.
Mistake: Confusing biomagnification with bioaccumulation in one organism
The food-chain levels are not mentioned.
Do this: State that concentration increases at each higher level of the food chain.
Usually costs: 1 mark.
Mistake: Naming wrong gases for acid rain
Carbon dioxide is written instead of sulphur dioxide and nitrogen oxides.
Do this: Learn: S and N make acids.
Usually costs: 1 mark.

Exam tips

Write definitions in one clear sentence, then give cause and effect.
Use the exact terms: greenhouse gases, dissolved oxygen, algal bloom, food chain.
Sequence process answers with first, then, finally.
Keep the five terms separate; do not blend the causes.

Practice questions on Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Heat-trapping gases that raise the earth's average temperature include:
(a) argon and helium
(b) carbon dioxide and methane
(c) oxygen and nitrogen
(d) neon and hydrogen
Hint
A greenhouse gas.
Answer
(b) carbon dioxide and methane.
Q2 · 1 mark · MCQBoard level
Thermal pollution harms aquatic life because warm water:
(a) contains more dissolved oxygen
(b) holds less dissolved oxygen
(c) is always acidic
(d) is richer in nitrates
Hint
Oxygen.
Answer
(b) holds less dissolved oxygen.
Q3 · 2 marks · Short answerHarder board level
State two consequences of global warming.
Hint
Glaciers, sea level, weather.
Answer
Melting glaciers and rising sea levels, and extreme weather.
Q4 · 2 marks · Short answerHarder board level
Why does a toxin such as DDT have the highest concentration in birds that eat fish rather than in the water itself?
Hint
Higher level of the food chain.
Answer
DDT is non-biodegradable and its concentration increases at each higher level of the food chain, so it is small in water, greater in plankton, more in fish and highest in birds that eat the fish.
Q5 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Detergents and sewage entering a pond can cause algal bloom.
Reason (R): They add nutrients such as nitrates and phosphates.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Nutrient enrichment.
Answer
(a).
Q6 · 2 marks · Short answerHarder board level
Give two ways in which burning waste and fossil fuels can harm the environment, using the terms in this topic.
Hint
Greenhouse gases and acid-forming gases.
Answer
Burning releases greenhouse gases such as carbon dioxide, adding to global warming; it also releases sulphur dioxide and nitrogen oxides that cause acid rain.
Q7 · 3 marks · Long answerHOTS / competency
A student says: 'Acid rain is the same as global warming because both come from burning fuels.' Evaluate this statement with two differences.
Hint
Different gases, different effects.
Answer
Both are linked to burning fuels, but they are different. Global warming is caused by greenhouse gases such as carbon dioxide and methane trapping heat and raising temperature; acid rain is caused by sulphur dioxide and nitrogen oxides forming acids. Effects also differ: melting glaciers and rising seas versus damage to monuments, crops and lakes.
Q8 · 5 marks · Case-basedHOTS / competency
A farm uses DDT near a lake, and fertiliser from its fields also drains into the lake. A researcher finds low oxygen in the lake and very high DDT in fish-eating birds. (a) Name the two processes. (b) Explain the cause of each. (c) Suggest one measure to reduce each problem.
Hint
Nutrients versus toxins.
Answer
(a) Eutrophication and biomagnification. (b) Nutrients (nitrates and phosphates) from fertiliser cause algal bloom and loss of oxygen; DDT is non-biodegradable and its concentration rises along the food chain. (c) Reduce fertiliser run-off (use less fertiliser, compost instead) and avoid or reduce use of persistent toxins like DDT.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Name two greenhouse gases.Show answer
Carbon dioxide and methane.
2.Which nutrients cause eutrophication?Show answer
Nitrates and phosphates.
3.Name a toxin that biomagnifies.Show answer
DDT (also mercury or lead).
4.Which acids are in acid rain?Show answer
Sulphuric and nitric acids.
5.Which industries cause thermal pollution?Show answer
Power plants and other industries that release heated water.

Global Warming, Acid Rain, Eutrophication, Biomagnification and Thermal Pollution: frequently asked questions

What is eutrophication?

Excess nutrient enrichment of a lake or pond that causes algal bloom and oxygen loss.

What is biomagnification?

The rise in concentration of a non-biodegradable toxin at each higher level of a food chain.

What causes acid rain?

Sulphur dioxide and nitrogen oxides combining with water vapour.

What is thermal pollution?

The release of heated water into rivers, lakes or the sea.