Environmental Sustainability, revision notes

Overview

Human activity puts real pressure on the environment, so this chapter looks at where that pressure comes from and how it can be managed. It covers the main threats to air, water and land, the greenhouse effect and its link to global warming, and how biochemical oxygen demand (BOD) is used to judge how polluted a water sample is.

You should be able to connect a specific human activity to a specific environmental effect rather than describing pollution in only general terms. For example, burning fossil fuels releases both greenhouse gases that contribute to global warming and other pollutants that lower air quality, and each effect should be explained separately in an exam answer.

The chapter then moves to how ecosystems are protected and used sustainably: preservation keeps an area untouched, conservation manages resources so they are not used up, and restoration repairs ecosystems that have already been damaged. Ozone layer depletion and eutrophication are two further threats often tested here, each with its own distinct cause-and-effect chain.

The final section covers green technology and sustainable development, including renewable energy sources, waste reduction and an Environmental Impact Assessment (EIA) carried out before a development project is approved. A strong answer names a specific technology or practice and explains the mechanism behind why it reduces environmental harm, rather than simply calling it 'eco-friendly'.

Air pollution and its sources (CS 25.1)

Human activities that cause air pollution include burning fossil fuels in power plants and vehicles, open burning of rubbish and agricultural waste, industrial emissions, and burning linked to deforestation. Specific pollutants released include carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter (haze) and carbon dioxide.

Different pollutants cause different specific effects: sulfur dioxide and nitrogen oxides dissolve in rainwater to form acid rain, which damages plants, corrodes buildings and acidifies soil and water bodies; particulate matter and smoke create haze that reduces visibility and irritates the respiratory system; carbon dioxide and methane contribute to the greenhouse effect.

Exam note: name a specific activity, a specific pollutant and a specific effect rather than writing that 'air pollution is bad' in general. Vehicle exhaust and industrial emissions are also two separate, commonly confused sources with different control measures, a catalytic converter for vehicles compared with an emission filter or scrubber for a factory chimney.

Water and land pollution (CS 25.1)

Sources of water pollution include untreated industrial effluent discharged into rivers, agricultural runoff carrying fertiliser and pesticide, untreated sewage, oil spills, and improper disposal of chemical waste.

Sources of land pollution include illegal dumping, non-biodegradable plastic waste, leachate from a landfill seeping into soil and groundwater, and excessive use of chemical fertiliser or pesticide that lowers soil quality.

The greenhouse effect and global warming (CS 25.1)

In the natural mechanism, shortwave solar radiation passes through the atmosphere and warms the Earth's surface, which then re-emits longwave (infrared) radiation. Greenhouse gases such as carbon dioxide, methane, water vapour and nitrous oxide absorb some of this heat and radiate it back down, keeping the average surface temperature warm enough to support life.

In the enhanced effect, human activities, burning fossil fuels, deforestation that reduces carbon dioxide absorption, livestock farming that produces methane, and waste decomposing in landfills, release extra greenhouse gases. This traps more heat and raises the average global temperature, which is global warming.

Consequences include melting polar ice and rising sea levels that threaten low-lying coastal areas, more frequent extreme weather such as heatwaves and intense storms, shifting rainfall patterns that affect agriculture, and coral bleaching caused by warmer, more acidic oceans. Exam note: global warming is a long-term trend in average temperature, not a description of any single hot day or storm.

Biochemical oxygen demand and eutrophication (CS 25.1)

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen used by microorganisms to decompose the organic matter in a water sample, usually measured as the drop in dissolved oxygen over a fixed incubation period. A higher BOD value indicates more organic pollution.

Comparing BOD values at different points along a river, such as upstream and downstream of a discharge point, lets a specific pollution source be identified and its severity judged, since BOD normally falls with distance from a point source as the pollutant is diluted and broken down.

The stages of eutrophication run in sequence: excess nutrients such as nitrate and phosphate from fertiliser runoff or sewage enter a body of water; algae and other aquatic plants grow rapidly, forming a dense bloom; the bloom blocks sunlight from reaching submerged plants, which then die; decomposers break down the dead plant and algal material, consuming large amounts of dissolved oxygen; the dissolved oxygen level then drops sharply, leaving too little oxygen for fish and other aquatic organisms, which suffocate. Exam note: describe this as a chain of cause and effect, not a single event.

Ozone layer depletion (CS 25.1)

The ozone layer in the stratosphere absorbs most of the sun's ultraviolet (UV) radiation, shielding living organisms at the surface.

Chlorofluorocarbons (CFCs), once common in aerosol propellants, refrigerants and foam-blowing agents, are stable enough to rise into the stratosphere. There, UV radiation breaks them apart, releasing chlorine atoms that break down ozone molecules; each chlorine atom can destroy large numbers of ozone molecules before it is finally removed, thinning the layer over time, notably over the polar regions.

A thinner ozone layer allows more UV-B radiation to reach the Earth's surface, raising the risk of skin damage, skin cancer, eye cataracts and harm to some crops and marine phytoplankton. International agreement under the Montreal Protocol phased out most industrial production of CFCs, and satellite monitoring has since recorded some recovery of the ozone layer.

Preservation, conservation and restoration of ecosystems (CS 25.2)

Preservation keeps an area completely free from human exploitation, such as a strict virgin forest reserve where logging, hunting and construction are all banned. Conservation allows regulated, sustainable use of a resource so it is not depleted, such as a logging concession under a selective-felling and replanting quota, or a fishing zone with a closed season and a minimum catch size.

Restoration actively repairs a damaged ecosystem, such as replanting a mangrove area cleared for aquaculture, or rehabilitating a former mining pond into a wetland.

A national park or marine park often combines all three approaches in different zones: a core zone may be preserved untouched, a buffer zone may allow conservation-based activity such as regulated ecotourism or research, and a degraded section may need active restoration. An exam answer should identify which zone or activity matches which term rather than treating an entire park as one category.

Exam note: name the specific practice, a total ban, a managed quota, or an active repair action, rather than describing an area only as 'protected', since that word alone does not show which of the three approaches is being used.

Environmental sustainability and sustainable practices (CS 25.3)

Sustainable development balances three pillars together: economic (continuing growth and livelihoods), social (community wellbeing, health and education) and environmental (protecting natural resources for the future), rather than pursuing economic growth at the environment's expense.

Practical sustainable practices span four areas: sustainable forestry through selective logging with a mandatory replanting ratio; sustainable fishing through quotas, closed seasons and a ban on gear that damages the seabed; sustainable agriculture through crop rotation, integrated pest management that reduces chemical pesticide use, and efficient irrigation; and the 3R principle, reduce, reuse, recycle, applied at household and industrial level to lower waste generation and resource extraction.

Exam note: link a named practice to the specific resource it protects and the mechanism by which it does so, for example, explain how crop rotation maintains soil fertility because different crops draw on different nutrients and some fix nitrogen, rather than simply stating that a practice 'helps the environment'.

Green technology (CS 25.4)

Green technology reduces environmental harm relative to conventional methods across four categories: renewable energy generation, cleaner production processes, efficient waste and wastewater treatment, and low-emission transport.

Choosing a green technology in practice (CS 25.4)

Choosing a green technology in practice involves weighing its environmental benefit against upfront cost, land requirement and reliability. An exam answer should evaluate one named technology against one named alternative, rather than asserting that green technology is automatically superior in every situation.

Green technology reduces environmental impact compared with fossil fuel alternatives, but no technology is entirely free of impact, manufacturing solar panels or wind turbines, for instance, still uses raw materials and energy, even though the technology itself produces no emissions while generating electricity.

Key concepts to master

• Threats to the environment, Human activities such as burning fossil fuels, deforestation and improper waste disposal cause air, water and land pollution, alongside a rise in greenhouse gases that drives global warming. Each threat has a distinct cause, so an exam answer should name a specific activity and its specific effect rather than describing pollution in general terms. Open burning and vehicle exhaust, for example, are two separate sources of air pollution with different pollutants and different control measures.
• Greenhouse effect and global warming, Greenhouse gases such as carbon dioxide and methane trap heat in the atmosphere that would otherwise escape into space, a natural effect that keeps Earth warm enough for life. Human activities release extra greenhouse gases, trapping more heat and raising the average global temperature, which is global warming.
• Biochemical oxygen demand (BOD), BOD measures how much oxygen microorganisms use to break down the organic matter in a water sample over a set time. A high BOD value means the water contains a lot of organic pollution, since more oxygen is used up, leaving less available for fish and other aquatic organisms. Comparing BOD values upstream and downstream of a discharge point is a common way to judge how much a specific source has polluted a river.
• Preservation, conservation and restoration, Preservation protects an area of nature and keeps it untouched by human use, such as a strict nature reserve. Conservation manages the wise, sustainable use of a resource so it is not exhausted, such as controlled fishing. Restoration actively repairs an ecosystem that has already been damaged, such as replanting a cleared forest.
• Green technology, Green technology reduces environmental harm compared with older methods, including renewable energy, recycling processes and cleaner production methods that release less pollution. Choosing a green technology usually involves weighing its environmental benefit against its cost and how practical it is to adopt widely. An electric vehicle, for example, produces no exhaust emissions itself, though the source of the electricity used to charge it also matters.
• Sustainable development, Sustainable development meets the needs of people today without reducing the ability of future generations to meet their own needs. It balances economic growth, social wellbeing and environmental protection together rather than treating environmental protection as separate from development. Planting a fast-growing replacement crop for every tree logged in a plantation forest is one practical example of this balance.
• Ozone layer depletion, The ozone layer in the upper atmosphere absorbs most of the sun's harmful ultraviolet (UV) radiation. Chemicals such as chlorofluorocarbons (CFCs), once common in aerosols and refrigerants, break down ozone molecules, thinning this layer and allowing more UV radiation to reach the Earth's surface, which raises the risk of skin damage and harm to some crops.
• Eutrophication, Eutrophication begins when excess nutrients, often from fertiliser runoff or untreated sewage, enter a body of water and cause algae to grow rapidly, forming a dense bloom. When the algae die, decomposers use up large amounts of dissolved oxygen breaking them down, which can leave too little oxygen for fish and other aquatic life.
• Renewable energy, Renewable energy sources, such as solar, wind and hydroelectric power, generate electricity without burning fossil fuels, which reduces the greenhouse gases released compared with coal or oil power plants. Adopting them at a larger scale usually requires weighing the upfront cost of infrastructure against the long-term reduction in emissions.
• Environmental Impact Assessment (EIA), An Environmental Impact Assessment is a formal study carried out before a development project, such as a new highway or factory, is approved. It identifies the project's likely effects on the surrounding environment so that mitigation steps can be planned, rather than approving a project without considering its environmental consequences.

Quick recall checklist

1. Can you define and explain Threats to the environment?
2. Can you define and explain Greenhouse effect and global warming?
3. Can you define and explain Biochemical oxygen demand (BOD)?
4. Can you define and explain Preservation, conservation and restoration?
5. Can you define and explain Green technology?
6. Can you define and explain Sustainable development?
7. Can you define and explain Ozone layer depletion?
8. Can you define and explain Eutrophication?
9. Can you define and explain Renewable energy?
10. Can you define and explain Environmental Impact Assessment (EIA)?

Frequently asked questions

More for Environmental Sustainability

Source:SRC-DSKP-EN