Biology Unit 4: Global Warming (AQA)

1: Short wave light radiation from the sun reaches earth.

2: Light energy is absorbed by earth and re emmited as long wave heat radiation.

3: Most of the heat energy passes through the gases in the atmosphere

4: Some heat energy is reflected back to earth by atmospheric gases.

Gases that contribute to the greenhouse effect are carbon dioxide, methane, water vapour and ozone.

The concentration of these greenhouse gases is increasing, leading to enhanced global warming.

We know greenhouse gas concentrations are increasing by measuring them in a number of ways.

For the past fifty years, the climate observatory at Mona Loa has been taking measurements of carbon dioxide concentrations.

Before that, we rely on indirect measurements from tree rings and ice cores. The thickness of annual tree rings indicate growth rate for that particular year. Tiny bubbles of air trapped in ice can be analysed.

The main causes for the rise in greenhouse gases are:

Methanogenic bacteria found in the intestines of cows and in flooded rice paddy fields produce methane. The increase in farming cows and rice have caused an increase in methane emissions. These bacteria are also found in landfill sites.

Burning fossil fuels such as oil and coal releases large amounts of carbon dioxide.

Deforestation increases carbon dioxide concentrations as less photosynthesis takes place and carbon dioxide is released when the trees decay or are burned.

Wild animals and plants must colonise further towards the poles in order to find a more suitable climate. If they cannot do this, they face extinction.

Cooler regions may be able to grow crops that were previously only grown in warmer climates. Other regions may suffer from crop failure as their climate becomes to warm and dry.

Pests that could not survive in cooler regions have now moved northwards. They can also spread disease further.