Global carbon cycle, carbon dioxide emissions and mitigation

Abstract

The carbon cycle is one of the biogeochemical cycles and describes the movement of carbon, in its many forms, within the biosphere, atmosphere, oceans and geosphere. The global carbon cycle involves the earth’s atmosphere, oceans, vegetation and soils of the terrestrial ecosystem and fossil fuels. Carbon in the form of inorganic and organic compounds, notably carbon dioxide (CO2), is cycled between different components of a system. For example, green plants absorb CO2 from the atmosphere during photosynthesis, also called primary production, and release CO2 back into the atmosphere during respiration. Another channel of exchange of CO2 is between the oceans and the atmosphere: CO2 dissolved in the oceans is used by marine biota in photosynthesis. Two important anthropogenic processes that contribute CO2 to the atmosphere are burning of fossil fuels and changes in land use. Fossil fuels, namely coal, oil and natural gas, are burnt in industries, power plants and automobiles. Land use is a broad term, which encompasses a host of essentially human-induced activities including conversion of natural ecosystems such as forests and grasslands to managed systems such as cropland, grazing land and settlements. Land conversion and other human activities such as extraction and burning of biomass and livestock grazing lead to soil degradation and emission of carbon contained in biomass and in soil to the atmosphere: CO2 emissions from the biosphere to the atmosphere result mainly from burning and decomposition of organic matter.