The amount of carbon dioxide varies naturally in a dynamic equilibrium with photosynthesis of land plants. The natural carbon sinks are:
*Soil is a carbon store and active carbon sink.
* Photosynthesis by terrestrial plants with grass and trees allows them to serve as carbon sinks during growing seasons.
* Absorption of carbon dioxide by the oceans via solubility and biological pumps.
Artificial carbon sinks are those that store carbon in building materials or deep underground (geologic carbon sequestration). No major artificial systems remove carbon from the atmosphere on a large scale yet.
Public awareness of the significance of  sinks has grown since passage of the 1997 Kyoto Protocol, which promotes their use as a form of carbon offset.