Editing IPCC:AR6/WGII/Cross-Chapter-Paper-3 (section)

=== CCP3.1.1 Concepts, Definitions and Scope ===

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Deserts and semiarid areas are in ‘drylands’, which comprise hyper-arid, arid, semiarid and dry sub-humid areas (Figure CCP3.1). Drylands cover about 45–47% of the global land area ( [[#Prăvălie--2016|Prăvălie, 2016]] ; [[#Koutroulis--2019|Koutroulis, 2019]] ) and are home to about 3 billion people residing primarily in semiarid and dry sub-humid areas (van der Esch et al., 2017). Drylands host unique, rich biodiversity ( [[#Maestre--2015|Maestre et al., 2015]] ) and provide important ecosystem services ( [[#Bidak--2015|Bidak et al., 2015]] ; [[#Lu--2018|Lu et al., 2018]] ), while dryland people have a rich cultural and historical heritage. Rural human populations are growing in some Mediterranean and tropical drylands, while many are rapidly urbanising (Guengant Jean-Pierre, 2003; [[#Tabutin--2004|Tabutin and Schoumaker, 2004]] ; [[#Denis--2009|Denis and Moriconi-Ebrard, 2009]] ), with varying impacts on ecosystem services and adaptive capacities. In recent decades, 6% of global megacities have been established in arid areas and 2% in hyper-arid desert areas ( [[#Cherlet--2018|Cherlet et al., 2018]] ), with many of these areas suffering from severe water security challenges ( [[#Stringer--2021|Stringer et al., 2021]] ). Dryland inhabitants in many developing countries are also experiencing poverty ( [[IPCC:Wg2:Chapter:Chapter-16#16.1.4.3|Section 16.1.4.3]] ), hunger, poor health, land degradation, and economic and political marginalisation ( [[#Mbow--2019|Mbow et al., 2019]] ; [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ), which sometimes limits their access to common pool resources. These challenges, together with a weak enabling environment, threaten opportunities to adapt to climate change.

The terms ‘desert’ and ‘desertification’ are subject to various interpretations due to the diverse components, processes and states they denote. Recognising ‘land degradation’ as a contested and perceptual term ( [[#Blaikie--1987|Blaikie and Brookfield, 1987]] ; [[#Behnke--2016|Behnke and Mortimore, 2016]] ; [[#Robbins--2020|Robbins, 2020]] ), this cross-chapter paper (CCP), defines land degradation as ‘a negative trend in land condition, caused by direct or indirect human-induced processes including climate change, expressed as long-term reduction or loss of at least one of the following: biological productivity, ecological integrity or value to humans’ ( [[#Olsson--2019|Olsson et al., 2019]] ). Desertification is land degradation in arid, semiarid and dry sub-humid areas ( [[#UNCCD--1994|UNCCD, 1994]] ). Following the above definitions, desertification is more common in arid and semiarid climates than in hyper-arid climates. When desertification does occur in arid and hyper-arid ecosystems it is often in oases and irrigated cultivated lands ( [[#Ezcurra--2006|Ezcurra, 2006]] ; [[#Dilshat--2015|Dilshat et al., 2015]] ). Hyper-arid areas, except wetlands such as oases, wadis and riverbanks, are excluded in the United Nations Convention to Combat Desertification (UNCCD) definition of desertification used here, yet many of the world’s deserts are in hyper-arid areas. Hyper-arid areas are therefore included when discussing deserts but not when discussing desertification. Deserts are not the end point in a desertification process ( [[#Ezcurra--2006|Ezcurra, 2006]] ). There is ''robust evidence'' of desertification in deserts, mostly driven by human activities and climate variability, expressed as loss of biological productivity, ecological integrity or value to humans to below their natural levels ( [[#Moridnejad--2015|Moridnejad et al., 2015]] ).

Interactions between climate change and desertification in drylands create challenges for both ecosystem and human resilience, affecting ecosystem services, biodiversity, food security, human health and well-being ( [[#Reed--2016|Reed and Stringer, 2016]] ). Dryland livelihoods that heavily rely on natural ecosystems face pressures, including high population growth rates, weak or poor governance, low investment, unemployment and poverty, market distortions and underestimates of the value of drylands ( [[#Stringer--2017|Stringer et al., 2017]] ; [[#Bawden--2018|Bawden, 2018]] ). These pressures intersect with broader societal challenges such as conflict and civil unrest ( [[#Okpara--2015|Okpara et al., 2015]] ; [[#Almer--2017|Almer et al., 2017]] ), which together, can contribute to human displacement ( [[IPCC:Wg2:Chapter:Chapter-16#16.2.3.10|Section 16.2.3.10]] ) in some drylands ( [[#Warner--2010|Warner, 2010]] ; [[#Abel--2019|Abel et al., 2019]] ). Nevertheless, evidence linking conflict with climate change and desertification is weak ( [[#Benjaminsen--2012|Benjaminsen et al., 2012]] ) and data are insufficient to draw robust conclusions.

Drylands yield important opportunities for adapting to and mitigating climate change. They offer abundant solar energy, which could support mitigation efforts, opportunities for cultural and nature-based tourism, rich plant biodiversity in some areas (e.g. Namibia), and extensive Indigenous knowledge and experience of adapting to dynamic climates ( [[#Christie--2014|Christie et al., 2014]] ; [[#Stringer--2017|Stringer et al., 2017]] ); for example, across West Asia and North Africa ( [[#Louhaichi--2010|Louhaichi and Tastad, 2010]] ; Hussein, 2011). Improved understanding of challenges and opportunities in drylands can be achieved by transdisciplinary, multi-scale and inter-sectoral approaches encompassing links between physical, biological, socioeconomic and institutional systems ( [[#Reynolds--2007|Reynolds et al., 2007]] ; [[#Stringer--2017|Stringer et al., 2017]] ).

[[IPCC:Wg2:Chapter:Chapter-3|Chapter 3]] of the IPCC Special Report on Climate Change and Land (SRCCL) focused on desertification ( [[#Mirzabaev--2019|Mirzabaev et al., 2019]] ), but links between climate change and deserts, desertification and semiarid areas have not been extensively considered in recent IPCC assessment cycles. Working Group II Assessment Report 5 noted that desertification contributes to atmospheric dust production, identifying desertification as needing consideration within climate change mitigation and adaptation governance and decision making ( [[#Boucher--2013|Boucher et al., 2013]] ; [[#Myhre--2013|Myhre et al., 2013]] ). This cross-chapter paper focuses on environmental and human aspects, finding that climate change impacts will intensify the challenges faced by dryland populations in advancing sustainable development. However, viable options exist for adapting to climate change, reducing desertification and supporting progress towards the Sustainable Development Goals (SDGs), particularly by combining modern science, IKLK, and livelihood and land management strategies that enable land-based adaptation, mitigation and nature-based solutions ( [[IPCC:Wg2:Chapter:Chapter-16#16.3.2.3|Section 16.3.2.3]] ).

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