CA, Energy Education, Encyclopedia, "Natural carbon cycle" ([Internet, 2022-09-20](https://energyeducation.ca/encyclopedia/Natural_carbon_cycle))
The natural carbon cycle is the flow of carbon naturally across the globe in various forms, such as carbon dioxide or methane. This carbon moves through the atmosphere, ocean, terrestrial biosphere, and lithosphere. The natural carbon cycle is kept very nearly in balance; animals and plants emit CO2 into the atmosphere through respiration, while plants absorb it through photosynthesis. The ocean also cycles CO2 with the atmosphere, in an almost perfect balance. [...] Human activities are known to be negatively affecting this cycle. [...] Human inputs [...] are causing a net increase in the atmosphere, soil, and oceans. This net increase stems from the fact that humans pull carbon-rich fossil fuels from underground that would otherwise not be part of the cycle, and introduce them into it via combustion.