Threats to the Environment

Human activities that threaten the environment

• Deforestation, clearing forests for logging, agriculture, or development, which destroys habitats.
• Pollution, the release of harmful substances into the air, water, or land.
• Overexploitation, harvesting resources such as fish or timber faster than they can be replenished.
• Urbanisation and industrialisation, converting natural habitats into towns, roads, and factories.

Air, water and land pollution

Air pollution comes from vehicle exhausts, factory emissions, and open burning, releasing gases such as carbon monoxide, sulfur dioxide, and particulates that harm respiratory health and contribute to acid rain. Water pollution results from untreated sewage, industrial effluent, and agricultural runoff containing fertilisers and pesticides entering rivers and seas, which can cause eutrophication and kill aquatic life.

Land pollution comes from improperly disposed solid waste and toxic chemicals contaminating soil.

The greenhouse effect and global warming

The greenhouse effect is a natural process in which gases such as carbon dioxide and methane trap heat radiated from the Earth's surface, keeping the planet warm enough to support life. Human activities such as burning fossil fuels and deforestation increase the concentration of these greenhouse gases in the atmosphere, intensifying the greenhouse effect beyond its natural level and causing global warming, a gradual rise in the Earth's average temperature.

Consequences for biodiversity and how this is examined

These threats reduce biodiversity by destroying habitats, poisoning organisms, and disrupting food chains, and can drive vulnerable species towards extinction. Global warming also shifts climate patterns, causing sea level rise and more extreme weather, which further stresses ecosystems already weakened by pollution and habitat loss.

SPM questions commonly ask you to link a named human activity to its environmental effect, explain the mechanism of the greenhouse effect using a labelled diagram, or discuss how a specific type of pollution affects a named ecosystem.

Worked exam-style question

Question. A lake near an oil palm plantation receives runoff containing fertiliser after heavy rain. Over the following weeks, the water turns green and cloudy, and large numbers of fish are found dead along the shore.

(a) Name the process responsible for the fish deaths. (b) Explain, in sequence, how the fertiliser runoff leads to the fish deaths.

(c) Suggest one way farmers could reduce this type of pollution.

Model answer. (a) Eutrophication. (b) Fertiliser runoff enters the lake and provides excess nitrates and phosphates, causing an algal bloom (rapid overgrowth of algae) on the water surface; the algae block sunlight from reaching plants below, which die and are broken down by decomposers that use up dissolved oxygen through respiration, leaving too little oxygen for the fish, which then suffocate and die.

(c) Farmers could apply fertiliser only in the recommended amount, avoid application before heavy rain, or leave a buffer strip of vegetation along the waterway to absorb runoff before it reaches the lake.

Practice question

Try this. A city's air quality index worsens noticeably every dry season due to smoke from open burning of agricultural waste combined with vehicle exhaust. (a) Name two gases released by this activity that harm human health or contribute to acid rain.

(b) State one consequence of this air pollution for a nearby forest ecosystem. (c) Suggest one action that would reduce this source of air pollution.

Exam tip

Key terms

• Greenhouse effect, the natural trapping of heat in the atmosphere by gases such as carbon dioxide, intensified by human activity.
• Global warming, the gradual rise in the Earth's average temperature, driven largely by an intensified greenhouse effect.
• Eutrophication, the over-enrichment of water with nutrients from runoff, leading to algal bloom and oxygen depletion.
• Sustainability, using natural resources to meet present needs without compromising the ability of future generations to meet theirs.

Source:SRC-DSKP-EN

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