Impact of Humans

Quick revise

Humans pose a huge threat to lives of animals, plants and their environment

Our impact is so great due to:

  • technologies that change the world so quickly
  • population increase
  • consumption of natural resources, and waste

Human Population Growth

Humans can adapt to survive in almost all habitats and climates. The human population is increasing rapidly and is threatening the environment.

The population will eventually be limited by these factors:

  • food and water supply
  • disease and pollution
  • over-crowding
  • sudden changes in climate

Household Waste, Sewage and Pollutants

Pollution is the addition of substances to the environment that may be harmful to living organisms. The increase in the human population is also increasing the amount of pollution.

Landfill sites

Most rubbish is buried in landfill sites and not all of it comprises safe materials. Even common household items can contain toxic chemicals such as poisonous metals. Many smoke alarms contain radioactive americium, for example.

Raw sewage is harmful to the environment. It kills aquatic organisms and harms human health. Sewage must be treated to make it safer before it can be released into the environment.

Carbon Dioxide

Carbon dioxide is released when fossil fuels are used. It is a greenhouse gas that can prevent heat escaping from the Earth into space. Increased emissions of carbon dioxide are causing a rise in carbon dioxide levels, which in turn contribute to global warming. People have different ‘carbon footprints’, depending on how much carbon dioxide their activities produce.

Sulphur Dioxide

Many fuels contain small amounts of sulphur compounds. When these fuels are burned sulphur dioxide is released into the air. Sulphur dioxide causes acid rain that can damage buildings, and kill plants and aquatic animals.


In the past, chlorofluorocarbons or CFCs were widely used in aerosol cans, refrigerators and insulating materials. CFCs destroy ozone in the upper atmosphere, leading to ozone depletion. This causes increased levels of ultraviolet light to reach the Earth’s surface.

Urbanisation & Industrialisation

More and more people are moving into the cities.

The effects:

  • increased pollution due to traffic, energy consumption and waste production
  • farmland is built on, land taken out of food production
  • loss of natural habitats, as cities and roads are built
  • rural communities and cultures dissolve as people leave to live in urban areas

Development of industries

The effects:

  • non-renewable fossil fuels are used for energy
  • release of greenhouse gases speeds up global warming

Air Pollution

The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations. Sulfur dioxide is released if the fuel contains sulfur compounds. This gas contributes to acid rain. Lichens can be used as air pollution indicators, especially of the concentration of sulfur dioxide in the atmosphere.

Lichens are plants that grow in exposed places such as rocks or tree bark. They need to be very good at absorbing water and nutrients to grow there. Rainwater contains just enough nutrients to keep them alive. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens and prevent them from growing. This makes lichens natural indicators of air pollution.

For example:

  • bushy lichens need really clean air
  • leafy lichens can survive a small amount of air pollution
  • crusty lichens can survive in more polluted air.

In places where no lichens are growing it is often a sign that the air is heavily polluted with sulfur dioxide.

Water Pollution

Oil spills cause a lot of harm to the environment, both at sea and on land

Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas. Many aquatic invertebrate animals cannot survive in polluted water, so their presence or absence indicates the extent to which a body of water is polluted.

Effect of Fertilisers

Intensive farming can damage the environment.

1.  Fertilisers containing plant nutrients are sprayed onto fields

2. Plants grow faster and boost crop yields.

3. Rain means may wash nutrients from the fields and into rivers and lakes (this is called run-off).

4. Eutrophication (hyper-nutirtion from fertisiler pollution) occurs which can kill almost everything living.

  • Algae grows fast using up lots of oxygen and blocking sunlight
  •  Plants begin to die providing food for microbes
  • Microbes increase the competition for oxygen
  • Water becomes de-oxygenated causing aquatic life to die

Effect of Pesticides

Pesticides used to kill insects and other crop damaging micro-organisms can effect the food chain

  • Pesticides can be abosrbed by small aquatic animals
  • Fish eat the animals, which have eaten pesticides
  • Birds eat the fish
  • Pesticides enters food chain

Fishing and Forestry


Unsustainability: the using up of resources faster than they are produced so that they will not continue in the future

Example: North Sea Cod are over-fished so are reproducing slower than are being caught. The effect of this means the cod population is heavily declining


Humans burn wood or clear land for farming causing deforestation:


  • destroys habitats
  • causes soil erosion leading to barren land and potential flooding
  • causes pollution from combustion
  • increased levels of carbon dioxide as loss of photosynthesis