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Estimates of total carbon storage in various important reservoirs.

Compiled by Jonathan Adams, Environmental Sciences Division, Oak Ridge National Laboratory, TN 37831, USA

Link to Introduction to the database

References directly cited in these pages (does not at present include secondary citations)

The following tables present some of the estimates for carbon reservoir sizes that have been put forward during the last twenty years or so. Some of these figures appear to be based on ad hoc studies and on extrapolation from very small amounts of data, but most seem to be based on fairly thorough work.

In general, the total range of all estimates published over the years for each reservoir should not be regarded as an indicator of the current range of uncertainty. In each case as more and more work has been done, so the general accuracy of the estimates has probably improved. Thus, the later-published estimates should generally be taken more seriously than the older ones. Nevertheless there is still always the possibility that some important aspect of any reservoir has been overlooked or poorly estimated, so that even the most recent estimates might eventually turn out to be in serious error.

It is important to distinguish between estimates that are intended to represent 'present-actual' carbon storage, and those intended to represent the 'present-potential' or past state. The present-potential is an elusive and hypothetical concept representing the distribution of vegetation types which it is thought would exist under presently existing climate conditions, if humans had not begun extensively modifying the environment through agriculture and forestry during the late Holocene. Sometimes it is taken to refer to the immediate pre-industrial era, but more often as a rough indicator of conditions about 4,000 years ago, just before the main anthropogenic deforestation phase.

Table 2:1a Previous global carbon storage estimates for vegetation. Note that some of these citations are secondary citations; these are marked (s.). Units are in gigatonnes of carbon (1 Gt = 1 billion tonnes = 1 Petagram = 1 x 1015 g).

Storage (Gt C) Reservoir type Author(s)
827 Gt (1.) Present actual land vegetation Whittaker & Likens (s.)
560 Gt (2.) Present actual land vegetation Olson et al. (1983)
550 Gt (3.) Present actual (1980s) vegetation IPCC (1990) (s.)
610 Gt (3.) Pre-industrial (pre-1700) vegetation IPCC (1990) (s.)
1080 Gt (4.) Land vegetation, 'prehistoric' times Bazilevich et al. (1971)
924 Gt Present potential ('prehistoric') vegetation Adams et al. (1990)
343 Gt (5.) Last Glacial Maximum vegetation Adams et al. (1990)
787 Gt (6.) Forest vegetation and soils (present day) Dixon et al. (1984)
110 Gt (7.) Global 'short-lived' biota (present day). Macdonald (1982)
450 Gt (7.) Global 'long-lived' biota (present day). Macdonald (1982)
350 Gt Coarse woody debris (present potential) Harmon (pers. comm.)
591 Gt (8.) Present-actual land vegetation Ajtay et al. (1975) (s.)

(1.) in Whittaker 1975, citing earlier work by Whittaker & Likens (s.).

(2.) 'Medium' value of 560 Gt, 'low' value 460 Gt, 'high' value 665 Gt. Based on a thorough study. For 'present actual' vegetation, these values are probably the most accurate to date.

(3.) From Siegenthaler & Sarmiento 1993, in a box model summary, using numbers approximating to 1990 IPCC assessment (s.).

(4.) Of this, several hundred Gt (240 Gt ) released on forest clearance (Olson 1974 (s.), cited in Olson et al. 1983), at an average rate of upto 0.1 Gt per year.

(5.) Based on palaevegetation maps of ecosystem areas.

(6.) Note that this estimate excludes non-forest ecosystems, but includes forest soil carbon.

(7.) Presumably derived from Olson et al. (1983), but source not specified. Presumably by 'short-lived' biota they mean herbaceous plant parts, fine roots, fruits etc.

(8.) Cited by Olson et al. (1983).

Table 2:1b: carbon storage totals for global soils. Note that some of these citations are secondary citations, marked by (s.).

Storage (Gt C) Reservoir type Author(s)
1115 Gt Soils, present potential ('prehistoric') Adams et al. (1990)
1395 Gt (1.) Peats + soils, present potential Adams et al. (1990)
1400 Gt (2.) Soils (?present-day) Macdonald (1992)
1640 Gt (2.) Soils + peat + litter Macdonald (1992)
1405 Gt (3.) Soils, present-day Bazilevich (1974) (s.)
3000 Gt (4.) Soils (+peats ?), present-day Bohn (1978) (s.)
1672 Gt (3.) Soils, present-day Bolin et al. (1979) (s.)
1477 Gt (5.) Soils, present-day Buringh (1983) (s.)
1515 Gt (6.) Soils (+peatlands?) present-day Schlesinger (1984)
787 Gt Forest soils only (+fine debris) Dixon et al. (1993)
1500 Gt (7.) Soils, in 1989 IPCC (1990) (s.)
1560 Gt (7.) Soils, in 'preindustrial' era. IPCC (1990) (s.)
860 Gt (8.) Peats, present-day Bohn (1976) (s.)
300 Gt (8.) Peats Sjors (1980) (s.)
202 Gt (8.) Peats Post et al. (1982)
377 Gt (8.) Peats Bohn (1976,82)
500 Gt (8.) Peats Houghton et al. (1985) (s.)
249 Gt (8.) Northern peatlands Arm.& Men. (1986). (s.)
210 Gt (8.) Boreal peatlands Oeschel (1989) (s.)
180-227 Gt (8.) Peats Gorham (1990) (s.)
461 Gt (9.) Subarctic and boreal peat Gorham (1992)
1576 Gt (10.) Global soils (present-day) Eswaran et al. (1993)
500 Gt (11.) Global peats Markov et al. (1988) (s.

(1.) incorporating 280 Gt for peats, a rough mid-way estimate from the range of sources in the literature (see below).

(2.) 1400 Gt in soils, plus 180 Gt in peat, plus 60 Gt in litter = 1640 Gt total. Figure of uncertain derivation.

(3.) Value cited by Schlesinger (1985); origonal reference not consulted.

(4.) Value cited by Schlesinger (1985). Based on extrapolation from data on South American soils. Generally viewed as too high a value by other authors. An estimated 300 Gt C was lost from soils since mid 1800s.

(5.) Value cited by Schlesinger (1985). With 537 Gt lost from soils since pre-history.

(6.) Based on a range of IBP and other data. With 36 Gt lost from soils since the mid-1800's.

(7.) Siegenthaler & Sarmiento 1993, in a box model summary, using numbers approximating to 1990 IPCC assessment.

(8.) Values cited by Schlesinger (1985).

(9.) Of the estimates for global peatland, the recent one of 461 Gt compiled by Gorham (1992) is generally seen as the most robust by experts in the field whom I have spoken to (e.g. R. Clymo, C. Kreminetski). It was based on a wide range of data sources including much recently gathered data, and compiled using a GIS-based approach. However, the latest estimates currently emerging from studies on Canadian peatlands (C. Kreminetski pers. comm., May 1994) seem to suggest figures of around 200 Gt for Canada alone, and if one takes the Russian and Scandinavean peatlands as together containing about twice this amount of carbon (a conservative estimate) this would give a total of around 600 Gt. This figure also does not include any tropical peatlands, which might well contain 100 Gt or more of peat carbon (H. Faure, unpublished calculations).

(10.) Eswaran et al. (1993) produced a revised set of estimates based on currently available data on soils, classified using the FAO-UNESCO system. However, their definition of 'soils' (meaning soils and peats) includes histosols (peats) only to a depth of 1m, which clearly greatly underestimates the size of the soil+peat reservoir.

(11.) Cited from the Russian by C. Kreminetski (Acad. of Sciences, Moscow), who regards this as a conservative estimate and probably an underestimate.

Table 2a:3 Marine, geologic and atmospheric reservoirs of carbon.

Storage Reservoir type Author(s)
750 Gt (1.) In atmosphere, CO2, CH4 (1990) IPCC (1990) (s.)
11,500 Gt (2.) Methane clathrates Macdonald (1992)
38,725 Gt (3.) Dissolved or in suspension in oceans IPCC (1990) (s.)
700 Gt (4.) Dissolved organic C; intermediate & surface waters IPCC. (1990) (s.)
4,000 Gt (5.) Fossil fuel Johns. & Ker. (s.)

(1.) currently increasing by 3 Gt per year (1ppm CO2 in atmosphere = 2.1286 Gt carbon).

(2.) Buried in seafloor, under permafrosts. A controversial figure. Considered much too high by many.

(3.) 38,725 Gt in oceans; 725 Gt (25 Gt organic, 700 Gt inorganic) in surface waters, 38,000 Gt (1,000 Gt organic, 37,000 Gt in inorganic form) in deep waters.

(4.) 1000 Gt total (organic and inorganic carbon) in surface ocean waters. D.O.C. 700 Gt. 38,000 Gt in intermediate and surface waters. Siegenthaler & Sarmiento 1993, in a box model summary, using numbers approximating to the 1990 IPCC assessment.

(5.) cited by Siegenthaler & Sarmiento (1993).

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