Page 31 - FAO-IPCC Expert meeting on climate change

Human-directed impacts on food and land-based ecosystems and their implications for food security
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2.2 Land degradation and desertification: between human drivers and climate change
The global soil assessment issued in 2015 by the Intergovernmental Technical Panel on Soils (ITPS), as part of the first Plenary Assembly of the Global Soil Partnership, lists several processes that affect land degradation, including soil erosion, decline of soil organic carbon and nutrient imbalance. A recent study documents the important role of temperature on carbon stock in boreal areas, concluding that one degree of additional warmth will result in a significant net loss of soil carbon into the atmosphere.11
Desertification is defined under the United Nations Convention to Combat Desertification (UNCCD) as land degradation in arid, semi-arid, and dry, sub-humid areas, climatically defined by their low values (<0.65) in an aridity index: the
ratio of long-term mean annual precipitation to the potential evapotranspiration. Desertification results from climatic and human factors. Activities to combat desertification include sustainable land management and soil restoration. As climate changes, so likely will the aridity index values for affected areas.
The recent release of the World Atlas of Desertification by the European Commission12 highlights a number of drivers that are putting at risk the production basis for food and it features the trends of several land degradation processes. According to this atlas, there is evidence that unsustainable activities by humans cause land degradation, reduce land productivity and extend desertification in several hotspots. Among the responses promoted by ITPS is the endorsement of the World Soil Charter by FAO member countries. This charter seeks to reverse the negative trends and approve voluntary guidelines for sustainable soil management while listing good practices that are directly applicable to all countries.
There are efforts to sustain the intensification of land through various objectives, including food production and meeting climate targets. For example, experiments are taking place in the United States to combine technical and economic approaches that integrate double cropping, reduce idle fallow, develop mechanization and improve degraded land. Likewise, Brazil aims to slow down deforestation in the Amazon through a range of incentives that include technological improvements, enforcement of existing regulations and engagement of those industries concerned
(e.g. soybean, livestock). Examples can similarly be cited for other countries, which would be highly useful in order to evaluate the causes and impacts. The conclusion is that there is no single solution that is sufficient either to tackle the multilayered causes and determinants of land use change or to calculate the environmental and economic costs.
2.3 Land degradation in rangelands: causes and consequences
Since rangelands occupy nearly 40 percent of terrestrial surface and livestock from rangeland are the economic backbone for millions of rural people, they will remain an invaluable and irreplaceable source of food, nutrition and income. Rangelands are an important pool of carbon soil and soil-based emissions are relatively limited but not when measured on a ruminant animal basis.
Rangeland degradation is a serious and persistent challenge caused by the transition from pastoral to agropastoral systems, with continuous grazing and increased animal stocking rates often going beyond the capacity of rangelands.13 Rangelands exhibit loss of diversity and reduced animal productivity, accompanied in some cases by increased desertification. In arid regions, abandoned cropland may be used for animal grazing and become part of rangelands,
a process that may be irreversible because of human pressure. Once land changes from cropping to rangeland or vice versa it is difficult to reverse for various reasons including changes in land tenure (with the new owners unwilling to return the land to previous use), induced intensification from human population pressure (which may be reversed unless population declines, say from outmigration). Conversely, any clearance of rangeland for cultivation or mining purposes is a major driver in land degradation. Even if cropland is abandoned rangeland may not easily be restored if its ecological resilience is lost. Moreover, with increasing conservation efforts in tropical forests, rangelands are increasingly
11 Crowther et al. (2016).
12 European Commission. (2016). EC/JRC. (2016).
13 There are differing views on this as shown in the substantial literature debate on equilibrium vs non-equilibrium systems (communication from an external reviewer).
FAO-IPCC Expert meeting on climate change, land use and food security