The report observes that grasslands cover 70 per cent of the world's agricultural lands, that more than a billion people depend directly on livestock for their living, and that rangelands store up to 30 per cent of the world's soil carbon stocks, plus carbon stored above-ground in shrubs and trees.

Globally, some 18-28 billion tonnes of carbon are estimated to have been lost as a result of rangelands degradation, and overgrazing has been estimated to release as much as 100 million tonnes of CO2 per year.

"In view of the vast extent of grasslands and rangelands and the degraded nature of large areas of these systems, the potential to sequester carbon through improved management is significant," the report's authors wrote.

"Such management practices include restoring organic matter to soils, reducing erosion, and decreasing losses resulting from burning and overgrazing."

The report also acknowledges the inter-relatedness of the problems and solutions: the solutions to climate change are not separate from the responses needed to make rangelands more resilient to drought, protect biodiversity and sustain the rural poor.

If a globally co-ordinated effort is made to improve management of rangelands with an aim to sequestering carbon, the report suggests that the world's dryland ecosystems have the potential to sequester a billion tonnes of carbon a year.

Improved grazing management is cited as the most important tool for sequestering carbon, with well-managed grazing usually preferable to leaving grasslands untouched.

"Reeder and Schuman reported higher soil C levels in grazed - compared to un-grazed - pastures, and noted that when animals were excluded, carbon tended to be immobilized in above-ground litter and annuals that lacked deep roots," the authors noted.

The report cites the work of Dr Christine Jones, the independent scientist who in 2005 convened a conference around the theme of soil carbon as a response to climate change, effectively putting the issue on the Australian agricultural agenda five years ahead of the FAO study.

* Click here to read a summary of the FAO report. The full report is also on the FAO website.