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There is increasing evidence that the level of carbon dioxide in the Earth’s atmosphere is rising. There is also evidence that humans are responsible for this rise.

Human factors increasing global warming

Some human activities increase the greenhouse gases in the atmosphere:

• Burning fossil fuels, eg coal, gas and oil - these release carbon dioxide into the atmosphere.
• Deforestation - trees absorb carbon dioxide during photosynthesis. If they are cut down, there will be higher amounts of carbon dioxide in the atmosphere.
• Dumping waste in landfill - when the waste decomposes it produces methane.
• Agriculture - agricultural practices lead to the release of nitrogen oxides into the atmosphere.

Natural factors increasing global warming

There are also natural factors which contribute to increased global warming:

• Orbital changes - the Earth has natural warming and cooling periods caused by Milankovitch cycles or variations in the tilt and/or orbit of the Earth around the Sun (Wobble, roll and stretch theory).
• Volcanic activity - during a volcanic eruption carbon dioxide is released into the atmosphere.
• Solar output - there can be fluctuations in the amount of radiation from the sun. If there is high amount emitted there will be an increase in Earth's temperatures.