|
GCOS Terrestrial ECV
Soil Carbon
Introduction: Soils represent the largest terrestrial carbon pool. On seasonal to decadal time scales, carbon sinks may be explained by changes in above-ground biomass, but on longer time scales soil carbon stocks become more relevant. Globally, the largest soil carbon stocks are primarily located in wetlands and peatlands, most of which are located on permafrost and in the Tropics. This soil carbon is vulnerable to changes in the hydrological cycle as well as to changes in permafrost dynamics (in the boreal zone), while tropical peatlands are severely threatened by deforestation and the transformation of primary forest to plantations. The total amount of carbon stored in soils and its distribution is still highly uncertain, and new estimates of carbon content at various depths are urgently needed.
The change in soil organic carbon is largely influenced by anthropogenic activities, particularly through the conversion of natural ecosystems to agricultural land. The soil organic carbon is contained within micro-aggregates, and a part is lost through respiration and erosion after their destruction. Soil organic carbon varies as a function of the texture, bulk density, microbiologic activity, and organic matter contained in the vegetation. Many authors have proposed quantification of the carbon stored in soils and study of the role of soils as both a source and sink of carbon. Comprehensive measurements of soil organic carbon involve identifying the different soil types and extracting soil samples. Since this is particularly labour-intensive and costly, a composite sampling method is necessary.
The identification of changes in soil carbon may be possible over long time scales at a limited number of sites identified under Action T33, e.g., those selected under Action T3, but additional and perhaps more accurate information on changes in soil carbon may be inferred from measurements of the annual cycle of carbon flux at these sites.
Such understanding and monitoring of greenhouse gas emissions and sinks is a fundamental step toward avoiding dangerous climate change. Obtaining verifiable and agreed estimates of regional CO2 sources and sinks is very important in the ongoing UNFCCC negotiation cycle to define emission reductions after the Kyoto Protocol. The consensus is that data assimilation systems that use both terrestrial and atmospheric data (i.e., GAW concentration data) will ultimately provide the required carbon fluxes at the required accuracy. Such systems are under development.
Earth observation data from various sources are useful to derive indicators of carbon flux (e.g., LAI, FAPAR), but these only document some of the carbon cycle processes. For example, FAPAR provides information on CO2 uptake, and satellite-based land surface imagery is essential for estimating emissions due to forest clearance. Assimilation of trace-gas concentration data, and column data provided by passive or active satellite sensors, together with a priori estimates of terrestrial fluxes and an atmospheric transport model, allow determination of large, continental-scale fluxes with uncertainties. The NOAA CarbonTracker scheme is probably the most advanced of these tools, but, as with all assimilation schemes, depends strongly on both the quantity and quality of atmospheric and surface data.
All FLUXNET sites maintain continuous CO2 flux measurements based on the eddy covariance technique covering various biomes around the world. Standards for data acquisition processing and archiving have been set in the framework of large international-scale projects (GTOS TCO, Global Carbon Project (GCP)) and continental-scale carbon projects (CarboEurope, CarboAfrica, US, Carbon Cycle Plan, etc). These standards should be implemented, preferably through centralised data quality-control centres and agreed protocols, such as those under the GAW umbrella. Integrated proposed carbon observing systems, such as ICOS, potentially provide the long-term monitoring capability to move the research network into a GCOS/GTOS baseline network.
(Source: WMO/IOC Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (2010 Update) GCOS-138/GOOS-184/GTOS-76/WMO-TD/No. 1523)
Satellite Observations: (under construction) (Satellite Missions)
References:
Data, Product, Metadata and Information Access
[ECV Matrix Main Page] [About the ECV Matrix] [Reference Documents] [Contact] [Updated June 6, 2010]
| Non-satellite or in-situ |
Satellite |
|
| |
|
