Clarifying 'carbon sequestration'

Despite widespread use in the literature, there seems to be little consensus on what the term 'carbon (C) sequestration' means. We differentiate between endogenous C, which fluxes within a system, and exogenous C, which fluxes between systems. Here we define 'endogenous C sequestration' as occurring when C fixation to release ratio is greater than one (fixation((a,s))/release((a,s)) >1), expressed at the briefest, annually (a) and budgeted within a specified system (s). We distinguish between sequestered C (stored for >1 year) and temporarily utilized biologic C (i.e., labile C present within a living organism), developing equations for herbaceous and woody plant systems. Standardized expression of C sequestration with incorporation of descriptors, for example 'somatic C sequestration((10 year,forest))', clarifies the location, timescale and system being considered and should allow for increased transparency and improved communication for climate change debates and C budgeting.