How does carbon dioxide get into Earth's atmosphere?

It is trapped in a lot of the things we burn as fuel (e.g. coal and oil) so when we burn it the carbon dioxide is released and goes into the atmosphere. Other human activities that add CO2 to the atmosphere include deforestation and cement manufacture. This accounts for about 3% of all annually produced CO2. Since this proportion is an addition to the total amount of atmospheric carbon dioxide, over time the level has increased by around 35 per cent from 260-280 parts per million (ppm) to the present 380 ppm.

Plants rotting, volcanoes and nature account for the remaining values. (97%)