Carbon sequestration, defined broadly, is the capture and storing of carbon for a long time so that it is not in the atmosphere in the form of carbon dioxide. A narrower definition refers to just the storage and not the capture. Carbon sequestration is important because the rising level of carbon dioxide in the atmosphere is both the leading cause of climate change and is also causing ocean acidification.
Carbon sequestration occurs naturally, most commonly as a result of the photosynthesis process in trees and other plants, which store carbon as they absorb carbon dioxide while growing, and through absorption by the oceans and other water bodies. Plants also release the oxygen from the carbon dioxide they absorb, and thus forests are often described as 'the lungs of the earth.' However, such natural carbon sequestration is no longer sufficient because of the vast amounts of carbon dioxide being released into the atmosphere by humans by the massive burning of fossil fuels.
Thus, there has been increasing interest in preserving and restoring of forests as a way to increase carbon sequestration, in addition to the desire to protect them in order to maintain biodiversity. Recently, much effort has also been devoted to developing artificial carbon sequestration processes. Although some progress has been made and some pilot plants have been put into operation, the scale of sequestration is still minuscule compared to the natural processes and will likely remain so for many years to come.