A reservoir that absorbs carbon is known as a carbon sink . However, at different stages in the carbon cycle, carbon dioxide is released from these reservoirs. When this happens carbon sinks become carbon sources . A balance of sorts between carbon storage and carbon dioxide release is essential to the maintenance of a habitable environment for most organisms. Plants act as carbon sinks because they normally use more carbon dioxide in the photosynthetic process than they release when they respire.
Respiration occurs when plants and animals die and decay, releasing carbon dioxide.
Human modifications of the Earth s land-based ecosystems, through deforestation, have reduced the ability of our forest ecosystems component of the carbon cycle to act as carbon sinks. To the extent which their carbon uptake is reduced, deforestation can be thought of as a carbon source. Human sources of greenhouse gases are sometimes referred to as anthropogenic sources. In the past 200 years, there has been a large increase in these sources of greenhouse gases, particularly carbon dioxide, methane and nitrous oxides. This has coincided with both the beginning of the Industrial Revolution as well as a concurrent surge in human population.