The global carbon cycle

The global carbon cycle comprises the carbon stocks, or pools, in the atmosphere, ocean, and terrestrial biosphere, and the fluxes that link these pools, driven by a complex set of biological and geochemical processes. This chapter summarizes our current understanding and quantification of the global carbon cycle, including the Keeling curve of atmospheric carbon dioxide (CO2) concentration, and introduces the main processes driving annual CO2 fluxes between the atmosphere and the terrestrial and oceanic carbon pools—photosynthesis, respiration, and physical air–sea gas exchange. The impacts on these processes of increasing atmospheric CO2 concentration, climate change, and eventual CO2 removal through the large-scale deployment of negative emissions technologies are described, and the chapter concludes with a summary of current R&D focus areas related to the global carbon cycle.