Editing IPCC:AR6/SRCCL/Chapter-4 (section)

==== 4.2.3.2 Indirect and complex linkages with climate change ====

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Many important indirect linkages between land degradation and climate change occur via agriculture, particularly through changing outbreaks of pests (Rosenzweig et al. 2001 <sup>[[#fn:r314|314]]</sup> ; Porter et al. 1991 <sup>[[#fn:r315|315]]</sup> ; Thomson et al. 2010 <sup>[[#fn:r316|316]]</sup> ; Dhanush et al. 2015 <sup>[[#fn:r317|317]]</sup> ; Lamichhane et al. 2015 <sup>[[#fn:r318|318]]</sup> ), which is covered comprehensively in Chapter 5. More negative impacts have been observed than positive ones (IPCC 2014b <sup>[[#fn:r319|319]]</sup> ). After 2050, the risk of yield loss increases as a result of climate change in combination with other drivers ( ''medium confidence'' ) and such risks will increase dramatically if global mean temperatures increase by about 4°C ( ''high confidence'' ) (Porter et al. 2014). The reduction (or plateauing) in yields in major production areas (Brisson et al. 2010 <sup>[[#fn:r320|320]]</sup> ; Lin and Huybers 2012 <sup>[[#fn:r321|321]]</sup> ; Grassini et al. 2013 <sup>[[#fn:r322|322]]</sup> ) may trigger cropland expansion elsewhere, either into natural ecosystems, marginal arable lands or intensification on already cultivated lands, with possible consequences for increasing land degradation.

Precipitation and temperature changes will trigger changes in land and crop management, such as changes in planting and harvest dates, type of crops, and type of cultivars, which may alter the conditions for soil erosion (Li and Fang 2016 <sup>[[#fn:r323|323]]</sup> ).

Much research has tried to understand how plants are affected by a particular stressor, for example, drought, heat, or waterlogging, including effects on below-ground processes. But less research has tried to understand how plants are affected by several simultaneous stressors – which of course is more realistic in the context of climate change (Mittler 2006 <sup>[[#fn:r324|324]]</sup> ; Kerns et al. 2016 <sup>[[#fn:r325|325]]</sup> ) and from a hazards point of view (Section 7.2.1). From an attribution point of view, such a complex web of causality is problematic if attribution is only done through statistically-significant correlation. It requires a combination of statistical links and theoretically informed causation, preferably integrated into a model. Some modelling studies have combined several stressors with geomorphologically explicit mechanisms – using the Water Erosion Prediction Project (WEPP) model – and realistic land-use scenarios, and found severe risks of increasing erosion from climate change (Mullan et al. 2012 <sup>[[#fn:r326|326]]</sup> ; Mullan 2013 <sup>[[#fn:r327|327]]</sup> ). Other studies have included various management options, such as changing planting and harvest dates (Zhang and Nearing 2005 <sup>[[#fn:r328|328]]</sup> ; Parajuli et al. 2016 <sup>[[#fn:r329|329]]</sup> ; Routschek et al. 2014 <sup>[[#fn:r330|330]]</sup> ; Nunes and Nearing 2011 <sup>[[#fn:r331|331]]</sup> ), type of cultivars (Garbrecht and Zhang 2015 <sup>[[#fn:r332|332]]</sup> ), and price of crops (Garbrecht et al. 2007 <sup>[[#fn:r333|333]]</sup> ; O’Neal et al. 2005 <sup>[[#fn:r334|334]]</sup> ) to investigate the complexity of how new climate regimes may alter soil erosion rates.

In summary, climate change increases the risk of land degradation, both in terms of likelihood and consequence, but the exact attribution to climate change is challenging due to several confounding factors. But since climate change exacerbates most degradation processes, it is clear that, unless land management is improved, climate change will result in increasing land degradation ( ''very high confidence'' ).

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