A new study has shown just how much carbon is stored globally in soils, and how important this is to climate change mitigation.

Published in Carbon Management, the study collates estimates of global soil organic carbon stocks, drawing on literature on soil carbon published over the last 60 years.

Researchers from Sussex, Cambridge in the UK and Italy found that most soil organic carbon is stored at northern latitudes, with a significant quantity locked up in permafrost regions. In cool, temperate regions more carbon is stored in soil than plants however in warm areas more carbon is stored in plants than in the soil.

The findings should help efforts to conserve carbon by focusing on conserving soils in temperate regions and plants in tropical regions.

Currently the majority of policies aimed at reducing CO2 emissions focus on carbon stored in plants, despite the fact that globally more carbon is stored in soils than in plants.

Practices such as agroforestry, reduced tillage and the use of manure can slow, halt or even reverse the loss of soil organic carbon.

The findings draw attention to how changes in land use – such as from forest to agriculture - contribute to rising atmospheric CO2. For example, up to 50% of soil organic carbon is lost when native vegetation is converted to cropland. The authors say emissions caused by changes in land use and land cover are the least understood component of the global carbon cycle.

The authors call for improved understanding of the global variation in carbon stocks, as well as their importance relative to carbon stored in vegetation. There needs to be better collection of data - on soil profiles, sampling soil carbon to greater depths, and the use of standardized sampling and modelling techniques - to improve estimates of global organic carbon stocks.

Download the article:

Scharlemann JPW, Tanner EVJ, Hiederer R & Kapos V (2014). Global soil carbon: understanding and managing the largest terrestrial carbon pool. Carbon Management 5(1) 81-91.