Human activities put growing pressure on the environment. The main threats are pollution, deforestation and global warming, all linked to the way we use resources.
Pollution
Pollution is the release of harmful substances (pollutants) into the environment. Its main forms are:
- Air pollution — from burning fossil fuels and open burning; causes haze, acid rain and breathing problems.
- Water pollution — from sewage, fertilisers and industrial waste; can cause eutrophication, where excess nutrients trigger algal blooms that use up oxygen and kill fish.
- Soil pollution — from pesticides, plastics and heavy metals.
Example
Fertiliser washed into a river adds nitrates and phosphates, causing algae to grow rapidly. When the algae die, decomposers use up the oxygen, and fish suffocate — this is eutrophication.
Deforestation
Deforestation is the large-scale clearing of forests for timber, agriculture and development. It causes soil erosion, flooding, loss of biodiversity and reduces the removal of carbon dioxide by trees.
Global warming
Burning fossil fuels and deforestation increase greenhouse gases such as carbon dioxide. These trap heat in the atmosphere (the greenhouse effect), raising the Earth's average temperature — global warming. Its effects include melting ice caps, rising sea levels, more extreme weather and shifts in the habitats of plants and animals. Another air-pollution problem is the thinning of the ozone layer by gases such as CFCs, which lets more harmful ultraviolet radiation reach the ground. These threats are linked: reducing the burning of fossil fuels and protecting forests helps to slow both pollution and global warming at the same time.
Key idea
More greenhouse gases → stronger greenhouse effect → global warming → climate change.
Remember
Eutrophication lowers oxygen in water; the greenhouse effect traps heat in the atmosphere.