World’s Soil Resources

IPCC Climate Region IPCC HWSDa
Tier 1 Topsoil Subsoil Soil Density
0-30 cm 0-≤30 cm 30-≤100 cm 0-≤100 cm 0-≤30 cm
Pg C Pg C Pg C Pg C* Mg C ha -1
Tropical Wet 52.4 62.6 65.4 128.0 66.5
Tropical Moist 94.5 78.6 72.3 150.9 45.0
Tropical Dry 99.9 67.3 69.0 136.2 22.0
Tropical Montane 49.8 29.6 26.5 56.1 40.3
Warm Temperate Moist 41.7 33.3 29.7 63.0 60.2
Warm Temperate Dry 42.9 38.9 39.6 78.5 30.8
Cool Temperate Moist 110.6 104.1 106.2 210.3 88.2
Cool Temperate Dry 56.9 52.2 50.0 102.2 42.7
Boreal Moist 137.3 162.0 194.7 356.7 117.6
Boreal Dry 30.3 32.0 37.0 68.1 84.0
Polar Moist 26.8 30.6 21.7 52.4 40.4
Polar Dry 7.2 8.0 4.3 12.3 40.5
Total 750.3** 699.3 716.4 1415.7 52.1
Table 6.1 Distribution of Soil Organic Carbon Stocks and Density by IPCC Climate Region
* Differences in topsoil and subsoil sum are due to data rounding
** Total includes 1.4 Pg C in undefined climate regions
The table shows that according to the processed data from HWSD, most SOC (356.7 Pg C) is stored in the
‘Boreal Moist’ climatic region. The second largest stock is found in the ‘Cool Temperate Moist’ region (210.3 Pg
C). With 117.6 Mg C ha -1 and 88.2 Mg C ha -1 , these climate regions also have the highest SOC densities. These
figures compare poorly with those presented by Post et al. (1982). A major source for the deviation is the
difference in the definition of the life zones as compared to the climatic regions, which lead to the delineation
of different areas.
Using the IPCC Tier 1 default values for organic C in mineral soils and retaining the stocks for organic soil
gives global organic C stock in the upper 30 cm of soil of 750.3 Pg C. This estimate is 51 Pg C (7.3 percent) higher
than the estimates derived from the HWSDa topsoil layer.
When comparing the two spatial SOC stock estimates by IPCC climate region, the stocks within each region
are broadly similar. A notable difference is for soils in the ‘Tropical Dry’ climate region. The IPCC Tier 1 SOC map
gives 99.9 Pg C for this zone, compared to 67.3 Pg C found in the HWSDa.
In the interpretation of the figure for SOC stocks of the IPCC Tier 1 Soil Organic Carbon layer, it should be
considered that organic soils were only added to the mineral soil layer in places where this soil type is not
found in association with mineral soils. Using all organic soil data is likely to increase the global SOC stocks.
However, the Tier 1 default values are calculated over a constant depth of 30cm, although some soils are
shallower, which in turn would reduce the stocks.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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