Last updated | August 21, 2025

Indicator information

Name

Soil organic carbon indicator (SOCI)

Unit

Amount of carbon stored in the soil (0 to 30 cm depth), expressed as density (in megagrams or tonnes per km²) and as total amount

Area of interest

The SOCI has been calculated and distributed through REST services at country, terrestrial ecoregion and protected area level and is available in KCBD - Global Biodiversity Data Viewer (GBDV) at country level.

Related targets

	Sustainable Development Goal 2 on zero hunger
	Sustainable Development Goal 13 on climate action
	Sustainable Development Goal 15 on life on land
	Global Biodiversity Framework Target 8
	Global Biodiversity Framework Target 10

Policy question

There are two main policy questions to which the SOCI indicator is relevant:

• How do protected areas contribute, through the conservation of soil resources, to the fertility, health and productivity of the ecosystems and to the livelihoods of the local communities that depend on these resources? Soil organic carbon (SOC) is the main component of soil organic matter, which is critical for the stabilization of soil structure, retention and release of plant nutrients, and water infiltration and storage in soil. SOC is therefore essential to ensuring soil health, fertility and food production. The loss of SOC indicates a certain degree of soil degradation, and can happen through unsustainable management practices such as excessive irrigation or leaving the soil bare, without significant vegetation cover.

• How do protected areas contribute to soil carbon storage and hence to offset the impacts of fossil fuel emissions and to climate change mitigation? Soils represent the largest terrestrial organic carbon reservoir. Carbon stored in soils worldwide exceeds the amount of carbon stored in phytomass and in the atmosphere, and is the second largest global carbon store (sink) after the oceans. Changes in land use and land cover can cause SOC decreases and carbon emissions, which are one of the largest sources of human-caused carbon emissions to the atmosphere. Protected areas may contribute to soil carbon retention and hence to the reduction of net emissions of greenhouse gasses responsible for climate change.

Use and interpretation

Soil organic carbon (SOC) is the carbon that remains in the soil after partial decomposition of any material produced by living organisms. Depending on local geology, climatic conditions and land use and management (amongst other factors), soils hold different SOC amounts.

The largest amounts of SOC are stored in the northern permafrost region, mostly in peat soils, where carbon accumulates in soils in huge quantities due to the low temperatures leading to low biological activity and slow decomposition of soil organic matter. In contrast, in dry and hot regions, plant growth is naturally scarce and only very little carbon enters the soil, leading to low SOC content. Climate change can also alter SOC levels, in contrasting magnitudes and directions depending on the considered regions.

Land cover and land use also have an important influence on SOC. Conversion of natural vegetation to cropland can cause large decreases in SOC levels. Unsustainable agricultural management practices such as excessive irrigation or leaving the soil bare are also drivers of important SOC losses, while the opposite is true for practices associated to sustainable soil management, such as mulching, planting cover crops, reduced or no tillage, moderate irrigation and judicious fertilization (Scharlemann et al., 2014; FAO, 2022; FAO and ITPS, 2018a, 2018b).

The SOCI provides useful information about the soil condition in protected areas, particularly when compared with other unprotected areas with similar environmental conditions, such as the unprotected buffers around protected areas. This information can contribute to identify potentially degraded areas, evaluate the conservation performance of protected areas, set restoration targets, and assess the contribution of protected areas to reduce net global carbon emissions.

Key caveats

The Global Soil Organic Carbon (GSOC) map (FAO, 2022 and FAO and ITPS, 2018a, 2018b), which has been used to obtain SOCI, only provides data on carbon stocks up to a depth of 30 cm. In parts of the world, however, organic soils can be up to 11 m deep, and they therefore contain more organic carbon than what is indicated by the GSOC map. For this reason, it is highly probable that SOCI underestimates the total amount of SOC, although the estimates it provides have been obtained using, for all locations, a common soil depth (0-30 cm), which therefore allows for comparisons across locations on that basis.

The global soil carbon map (GSOC) is based on national SOC maps and national soil sampling schemes, which may differ in their sampling period, intensity and spatial distribution. In addition, even when all countries have followed a common methodological approach to derive the national SOC maps, there might be national specifies and differences in the details of the approaches used to produce the 1 km resolution maps from the soil sampling data. All these reasons suggest the need for caution in the comparison of the SOCI values for protected areas located in different countries.

SOC mapping involves making predictions or extrapolations at locations where no soil measurements were taken. This inevitably leads to some prediction errors because soil spatial variation is the result of a complex set of factors and processes that cannot be modeled perfectly at a national or global level. Given that the soil sampling schemes are commonly focused preferentially on areas for agricultural production, the number of soil samples taken within protected areas may be low in different countries. This would imply that the SOCI values are more largely based on predictions, rather than on actual measurements, in these protected areas compared to agricultural-dominated areas.

Because the SOCI is computed within the boundaries for each protected area, results will be affected by the accuracy of the available protected area boundaries.

Indicator status

The GSOC map, developed by FAO, is publicly available for visualization and download and is described in detail in FAO (2022), in FAO and ITPS (2018b). Further information is available at http://www.fao.org/global-soil-partnership/pillars-action/4-information-and-data-new/global-soil-organic-carbon-gsoc-map. The assessment of SOCI in protected areas has not been published but a similar approach can be found in Campbell et al. (2008).

Available data and resources

Data

SOCI values are provided at country level on the KCBD Global Biodiversity Data Viewer  website.

Update frequency

Planned annually.

Code

The procedure for the computation of the indicator, which currently involves the use of a wide range of software to handle the different steps, is documented in Juffe Bignoli et al. (2024).

Methodology

The SOCI is based on the information provided by the global soil organic carbon (GSOC) map (version 1.6.0), which quantifies, with a spatial resolution of 1 km, the amount of organic carbon (Mg/km²) stored in the soil worldwide, considering a soil depth of up to 30 cm. The GSOC map was produced through a participatory approach in which countries developed their capacities and stepped up efforts to compile all the available soil information at the national level. It is the result of the combination of national SOC maps, with one SOC map developed independently in each country but following a common methodological approach for all countries. The GSOC map, and hence the SOCI values, build on the information from soil samples were carbon measurements were made in each country. The information from these samples was used to build, in each country, a full continuous SOC map through predictions or extrapolations, involving covariates that were shown to be related to SOC levels in the sampled locations and hence useful to provide SOC estimates in the unsampled locations.

The GSOC map data, with a spatial resolution of 1 km, have been submitted to the standard procedure for continuous raster datasets described in details Juffe Bignoli et al. (2024) in order to derive the minimum, maximum and mean (Mg/km²) SOC, as well as the total SOC stored (Mg) in each country, ecoregion and protected area. UNESCO Biosphere Reserves were discarded as well as protected areas with known areas but undefined boundaries.

Input datasets

References

Campbell, A., et al. (2008). Carbon storage in protected areas. Technical report. UNEP World Conservation Monitoring Centre. https://archive.org/details/carbonstorageinp08camp/page/3

Dinerstein et al. (2017), An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm, BioScience, Volume 67, Issue 6, June 2017, Pages 534–545, https://doi.org/10.1093/biosci/bix014

FAO and ITPS. (2018a). Global Soil Organic Carbon Map (GSOC map) Version 1.2.0 - Leaflet. Rome, Italy. 5 pp.

FAO and ITPS. (2018b). Global Soil Organic Carbon Map (GSOC map) - Technical Report. Rome. 162 pp.

FAO (2022). Global Soil Organic Carbon Map – GSOCmap v.1.6. Technical report. Rome. https://doi.org/10.4060/cb9015en

Juffe-Bignoli et al. (2024) Delivering Systematic and Repeatable Area-Based Conservation Assessments: From Global to Local Scales. Land 2024, 13, 1506. https://doi.org/10.3390/land13091506

Lázaro, C., Mandrici, A., Delli, G., Caudullo, G., Bourgoin, C. et al., Challenges in integrating global environmental data with GISCO administrative layers – A GIS perspective, Publications Office of the European Union, 2025. https://dx.doi.org/10.2760/8183010

Scharlemann, J.P.W., Tanner, E.V.J., Hiederer, R., & Kapos, V. (2014). Global soil carbon: understanding and managing the largest terrestrial carbon pool. Carbon Management, 5: 81-91, https://doi.org/10.4155/cmt.13.77

UNEP-WCMC & IUCN (2025). Protected Planet: The World Database on Protected Areas (WDPA) [On-line], [January/2025], Cambridge, UK: UNEP-WCMC and IUCN. www.protectedplanet.net