Acid Rain and Global Warming


Carbon Monoxide

Carbon monoxide, CO, is produced when fuels burn in a limited amount of air. It is a colourless, odourless and tasteless gas. Carbon monoxide passes into the red blood cells after breathing it in. It binds more strongly to haemoglobin than oxygen does, so the blood will be able to carry less oxygen than it should. This can cause tiredness, unconsciousness and even death.

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Sulfur Dioxide

Fossil fuels naturally contain sulfur compounds. These produce sulfur dioxide, a gas with a sharp, choking smell when the fuel is burned. When sulfur dioxide dissolves in water droplets in clouds, it makes the rain more acidic than normal. This is called acid rain.

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Acid Rain

Acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.

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Lichens can be used as biological indicators of sulfur dioxide pollution. They grow in exposed places such as rocks or tree bark, which means they easily absorb 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.

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Green House Gases

Greenhouse gases in the atmosphere absorb heat energy and prevent it escaping into space. This keeps the Earth warmer than it would be without these gases. Greenhouse gases are not a bad thing in themselves, but too much of them in the atmosphere leads to an increase in the greenhouse effect and global warming.

There are many greenhouse gases but these are some of the most important:

- water vapour, H2O

- carbon dioxide, CO2

- methane, CH4

- nitrous oxide, N2O

- CFCs (chlorofluorocarbons)

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The Greenhouse Effect

1. Sunlight passes through the Earth’s atmosphere.

2. The ground warms up and heat is emitted from the Earth’s surface.

3. Some heat escapes into space but some is absorbed by greenhouse gases. It is re-emitted and does not escape.

4. The Earth’s atmosphere warms up.

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Adding to Greenhouse Gases

Human activities are adding to the quantities of greenhouse gases in the atmosphere.


Farming causes the production of methane and nitrous oxide.

- Rice paddy fields produce methane, as do cattle. As the number of rice fields and cattle have increased, so has the amount of methane in the atmosphere.

- Nitrous oxide is released from animal waste and as a result of using fertilisers for crops

Using fuels

Fossil fuels produce carbon dioxide when they are burned. When land is cleared for timber and farms (deforestation), there are fewer trees to remove carbon dioxide from the atmosphere for photosynthesis. If the fallen trees are burned or left to rot, additional carbon dioxide is released into the atmosphere.

These factors are particularly important in tropical areas, where forests might be cleared to make way for cattle farms. Then, not only are fewer trees left to absorb carbon dioxide, but the burning trees release carbon dioxide and the cattle release methane.

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Carbon Dioxide

As the concentration of greenhouse gases in the atmosphere has increased, so too has the average global temperature. This is what scientists mean when they talk about global warming. Carbon dioxide emissions from human activities have increased the amount of this gas in the atmosphere

Carbon dioxide in the atmosphere

The concentration of carbon dioxide in the atmosphere was 0.028% before the start of the Industrial Revolution in the 18th century. Since then, the concentration has risen rapidly. It reached 0.040% in mid-2013.

Global average temperature

The average global temperature has changed over time. Although some years are colder than the year before, there has been a trend for the average temperature to rise.

The general increase in global average temperature follows a similar trend to the percentage of carbon dioxide in the atmosphere. This does not in itself show that there is a causal relationship.

However, taking into account other data, the consensus of scientific opinion is that the two are linked this way. This is why we are encouraged to reduce emissions of carbon dioxide, for example by walking instead of taking the car.

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Global Warming

A rise of just a few degrees in world temperatures will have a dramatic impact on the climate:

- global weather patterns will change

- polar ice caps will melt

Climate change will cause drought in some places and flooding in others. Increased sea levels from warming oceans and melting glaciers will cause increased coastal erosion and flooding of low-lying land.


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Recycling can reduce the amount of waste and pollution in the environment.

Many materials can be recycled, including:

- glass

- metal

- paper

- plastic


Glass can be melted and remoulded. Less energy is needed to do this than to make new glass from its raw materials. However, different coloured glass must be sorted and transported to the recycling plant.


It takes less energy to melt and remould metals than it does to extract new metals from their ores. Aluminium is a valuable metal that melts at a relatively low temperature and is particularly attractive for recycling. However, a lot of metals are alloys, and it can be difficult to sort different metals for recycling.


Paper can easily be recycled. The process takes less energy than making paper from trees. However, paper can only be recycled a few times before its fibres become too short to be useful


Crude oil is the raw material for making plastics. It is a non-renewable resource, so recycling plastic helps to conserve it. Recycling also stops plastic going to landfill sites or causing a litter nuisance. Different types of plastics have to be sorted out before recycling.

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