Module One 11.8 How do humans affect the environment?
Introduction
Humans often upset the balance of different populations in natural ecosystems, or change the environment so that some species find it difficult to survive. With so many people in the world, there is a serious danger of causing permanent damage not just to local environments but also to the global environment.
Losing land
Humans reduce the amount of land available for other animals and plants by:
1. Building
Humans use the land to build for example houses, schools, offices and factories.
2. Quarrying
Humans need materials such as stone to build with. They will dig these substances from the land and create areas of land that cannot support animal or plant life while the land is being excavated.
3. Farming
Large areas of land are used to provide food for humans. Creating these large fields destroys hedgerows, the habitat for many small animals. Often only one type of crop is grown, limiting the area of land for growth of other types of plant.
4. Dumping waste
Tips take up a large area of land and humans are constantly adding to waste sites.
Pollution
Human activity also causes pollution.
1. Water pollution
Human activity can upset the ecosystem of a stream or river and harm plant life.
· Chemical pollution kills water life. The chemicals may also end up in drinking water supplies.
· If sewage gets into a stream it leads to less oxygen being available in the water. Fish and other aquatic animals will then die.
· Fertilisers dissolve in rainwater and can be washed out of the soil. This is called leaching. Like sewage, fertilisers put unwanted nutrients into a stream and will eventually cause fish and other aquatic animals to die.
2. Land pollution
Land can be polluted with toxic chemicals, such as pesticides and herbicides (weed-killers). Farmers spray these chemicals onto their crops to increase the amount of crop that survives for humans to eat. These chemicals can be washed from the land and into water by rain.
3. Air pollution
The air can be polluted with smoke and gases such as sulphur dioxide.
Acid rainWhen coal, oil and gas (fossil fuels) are burned, the waste gases produced include sulphur dioxide, nitrogen oxides, as well as carbon dioxide.
However, unless the sulphur dioxide and nitrogen oxides (not carbon dioxide!!!!!) are removed, these gases will dissolve in rainwater and make it strongly acidic. Acid rain may damage trees and plants. If the water in lakes becomes strongly acidic plants and animals cannot survive.
The 'greenhouse effect'Do not confuse this with acid rain or the ozone layer. You do not need to know anything about the ozone layer, and if you mix up the science between acid rain the greenhouse effect or the ozone layer in your exam, you can be negatively marked!!!
What is causing the greenhouse effect?
Carbon dioxide is also released when fuels are burnt. Plants take in carbon dioxide from the atmosphere (photosynthesis). Plants and animals give out carbon dioxide during the process of respiration (including decomposing bacteria).
Large scale deforestation in tropical areas, for timber and to provide land for agriculture, has:
1) Increased the release of carbon dioxide into the atmosphere due to burning the timber and the activities of microbes.
2) Reduced the rate at which the carbon dioxide is removed from the atmosphere via the process of photosynthesis. This means that less carbon dioxide is locked up as wood.
Methane is another greenhouse gas. The amount of this gas entering the atmosphere has also increased. This is due to:
1) An increase in the number of cattle who give it off as a waste product.
2) An increase in the amount of rice fields that give off methane as it grows.
So how does the Greenhouse Effect work?
Solar radiation passes through the clear atmosphere
Most radiation is absorbed by the Earth's surface and warms it.
Some solar radiation is reflected by the Earth and the atmosphere.
Infrared radiation is emitted from the Earth's surface.
Some of the infrared radiation passes through the atmosphere and some is absorbed and re-emitted in all directions by greenhouse gas molecules e.g. methane. This causes the Earth's surface to warm up
What could the effects of Global warming be?
This process is thought to be increasing the temperature of the climate and increasing the sea level. Over the next hundred years the average temperature may rise by only a few degrees but this could drastically affect world climates.
Nutrient Cycles
Human Impact on the Environment
School Net - Different Ways the Environment is Being Harmed
Encyclopedia of Sustainable Development