1. Burning of fossil fuels.
Under natural conditions the release of carbon from fossil fuels occurs slowly, as they are subducted into the mantle, and CO2 is released through volcanic activity. However, humans are heavily reliant on fossil fuels, and extract it from the lithosphere in great quantities. Burning coal, oil, natural gas, and other fossil fuels – for industrial activity and power generation for example, removes the carbon from the fossil fuels and emits it as CO2 into the atmosphere.