Global Warming (AQA GCSE Biology): Revision Note

Global warming

• Global warming is the long-term increase in Earth's average temperatures, resulting from human activities

• This temperature increase is taking place due to an increase in greenhouse gas emissions, particularly the release of:

  • carbon dioxide: produced during the combustion of fossil fuels, and increased by deforestation (fewer trees take in carbon dioxide for photosynthesis, and the cleared trees are often burned)

  • methane: produced by anaerobic breakdown of biological material, cattle digestion, and rice paddy fields

• Carbon dioxide and methane trap heat in the atmosphere, so less heat escapes from the Earth into space

Biological consequences of global warming

• The consequences of global warming due to an enhanced greenhouse effect include:

  • ocean temperatures increasing, causing:

    • melting of polar ice caps

    • habitat loss

  • extreme weather patterns, e.g.:

    • drought

    • increased rainfall

    • severe storms

  • changes in species distribution

    • As conditions change, organisms migrate to find more suitable habitats; this can cause changes in disease spread, disruption to ecosystems and local extinctions

  • changes to plant growth

    • Higher temperatures and carbon dioxide concentrations can temporarily increase rates of photosynthesis in plants

    • In the longer term this will also be affected by factors such as water availability, pollinator health and soil nutrients

The evidence for global warming

• There is scientific consensus that global warming is happening and that human activities are largely responsible for recent changes

  • This scientific consensus is based on peer reviews of thousands of scientific research papers

• Although scientific modelling can make some predictions, it is difficult to say for certain what the consequences of global warming will be in different parts of the world