3 Anthropogenic causes of global warming

3.1 What are the main causes of the enhanced greenhouse effect?

The most significant greenhouse gas is CO₂. When fossil fuels such as oil, coal and gas are burnt, CO₂ is released into the Earth's atmosphere. The cutting down of forests also increases the concentration of CO₂ in the atmosphere, as growing forests remove CO₂ from the atmosphere by absorbing it in wood, leaves and soil; this CO₂ is released back into the atmosphere when forests are burnt. The human activities of deforestation and fossil fuel use are the major anthropocentric causes of climate change.

But there are other important greenhouses gases, such as methane, nitrous oxide and water. And aerosols have a cooling effect. All of these, and others, are taken into consideration in arriving at the main conclusion above, and summarised in a neat diagram in the FAQ ‘How do human activities contribute to climate change and how do they compare with natural influences?’ from the IPCC.

• In a short video with Sir David Attenborough, computer models are used to compare the natural and human causes of global warming.