Editing IPCC:AR6/WGIII/Chapter-7 (section)

==== 7.4.2.5 Reduce Degradation and Conversion of Grasslands and Savannas ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Grasslands cover approximately 40.5% of the terrestrial area (i.e., 52.5 million km 2 ) divided as 13.8% woody savanna and savanna; 12.7% open and closed shrub; 8.3% non-woody grassland; and 5.7% is tundra ( [[#White--2000|White et al. 2000]] ). Sub-Saharan Africa and Asia have the most extensive total area, 14.5 and 8.9 million km 2 , respectively. A review by [[#Conant--2017|Conant et al. (2017)]] reported based on data on grassland area ( [[#FAO--2013|FAO 2013]] ) and grassland soil carbon stocks ( [[#Sombroek--1993|Sombroek et al. 1993]] ) a global estimate of about 343 PgC (in the top 1 m), nearly 50% more than is stored in forests worldwide ( [[#FAO--2007|FAO 2007]] ). Reducing the conversion of grasslands and savannas to croplands prevents soil carbon losses by oxidation, and to a smaller extent, biomass carbon loss due to vegetation clearing (SRCCL, Chapter 6). Restoration of grasslands through enhanced soil carbon sequestration, including (i) management of vegetation, (ii) animal management, and (iii) fire management, was also included in the SRCCL and is covered in [[#7.4.3.1|Section 7.4.3.1]] . Similar to other measures that reduce conversion, conserving carbon stocks in grasslands and savannas can be achieved by controlling conversion drivers (e.g., commercial and subsistence agriculture, see [[#7.3|Section 7.3]] ) and improving policies and management. In addition to mitigation, conserving grasslands provide various socio-economic, biodiversity, water cycle and other environmental benefits ( [[#Claassen--2010|Claassen et al. 2010]] ; [[#Ryals--2015|Ryals et al. 2015]] ; [[#Bengtsson--2019|Bengtsson et al. 2019]] ). Annual operating costs, and opportunity costs of income foregone by undertaking the activities needed for avoiding conversion of grasslands making costs one of the key barriers for implementation ( [[#Lipper--2010|Lipper et al. 2010]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The SRCCL reported a mitigation potential for reduced conversion of grasslands and savannas of 0.03–0.12 GtCO 2 -eq yr –1 ( [[#Griscom--2017|Griscom et al. 2017]] ; [[#IPCC--2019|IPCC 2019]] ) considering the higher loss of soil organic carbon in croplands ( [[#Sanderman--2017|Sanderman et al. 2017]] ). Assuming an average starting soil organic carbon stock of temperate grasslands ( [[#Poeplau--2011|Poeplau et al. 2011]] ), and the mean annual global cropland conversion rates (1961–2003) ( [[#Krause--2017|Krause et al. 2017]] ), the equivalent loss of soil organic carbon over 20 years would be 14 GtCO 2 -eq, for example, 0.7 GtCO 2 yr –1 (SRCCL, Chapter 6). IPCC AR5 and AR4 did not explicitly consider the mitigation potential of avoided conversion of grasslands-savannas but the management of grazing land is accounted for considering plant, animal, and fire management with a mean mitigation potential of 0.11–0.80 tCO 2 -eq ha –1 yr –1 depending on the climate region. This resulted in 0.25 GtCO 2 -eq yr –1 at USD20 tCO 2 –1 to 1.25 GtCO 2 -eq yr –1 at USD100 tCO 2 –1 by 2030.

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Unlike most of the measures covered in [[#7.4|Section 7.4]] , there are currently no global, spatially explicit mitigation potential estimates for reduced grassland conversion to generate technical and economic potentials by region. Literature developments since AR5 and SRCCL are studies that provide mitigation estimates in one or a few countries or regions. Modelling experiments comparing Californian forests and grasslands found that grasslands resulted in a more resilient carbon sink than forests to future climate change ( [[#Dass--2018|Dass et al. 2018]] ). However, previous studies indicated that precipitation is a key controller of the carbon storage in these grasslands, with the grassland became a carbon sink in 2005, when the region received relatively high spring precipitation ( [[#Ma--2007|Ma et al. 2007]] ). In North America, grassland conversion was the source for 77% of all new croplands from 2008–2012 ( [[#Lark--2015|Lark et al. 2015]] ). Avoided conversion of North American grasslands to croplands presents an economic mitigation potential of 0.024 GtCO 2 -eq yr –1 and technical potential of 0.107 GtCO 2 -eq yr –1 ( [[#Fargione--2018|Fargione et al. 2018]] ). This potential is related mainly to root biomass and soils (81% of emissions from soils). Estimates of GHG emissions from any future deforestation in Australian savannas also point to the potential mitigation of around 0.024 GtCO 2 -eq yr –1 ( [[#Bristow--2016|Bristow et al. 2016]] ). The expansion of the Soy Moratorium (SoyM) from the Brazilian Amazon to the Cerrado (Brazilian savannas) would prevent the direct conversion of 3.6 Mha of native vegetation to soybeans by 2050 and avoid the emission of 0.02 GtCO 2 -eq yr –1 ( [[#Soterroni--2019|Soterroni et al. 2019]] ).

'''Critical assessment and conclusion.''' There is ''low confidence'' that the global technical mitigation potential for reduced grassland and savanna conversion by 2050 is 0.2 (0.1–0.4) GtCO 2 yr –1 , and the economic mitigation potential (&lt;USD100 tCO 2 –1 ) is 0.04 GtCO 2 yr –1 . Most of the carbon sequestration potential is in below-ground biomass and soil organic matter. However, estimates of potential are still based on few studies and vary according to the levels of soil carbon, and ecosystem productivity (e.g., in response to rainfall distribution). Conservation of grasslands presents significant benefits for desertification control, especially in arid areas (SRCCL, Chapter 3). Policies supporting avoided conversion can help protect at-risk grasslands, reduce GHG emissions, and produce positive outcomes for biodiversity and landowners ( [[#Ahlering--2016|Ahlering et al. 2016]] ). In comparison to tropical rainforest regions that have been the primary target for mitigation policies associated to natural ecosystems (e.g., REDD+), conversion grasslands and savannas has received less national and international attention, despite growing evidence of concentrated cropland expansion into these areas with impacts of carbon losses.

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