Editing IPCC:AR6/SR15/Chapter-3 (section)

==== 3.6.2.2 Biophysical feedbacks on regional climate associated with land-use changes ====

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Changes in the biophysical characteristics of the land surface are known to have an impact on local and regional climates through changes in albedo, roughness, evapotranspiration and phenology, which can lead to a change in temperature and precipitation. This includes changes in land use through agricultural expansion/intensification (e.g., Mueller et al., 2016) <sup>[[#fn:r1299|1299]]</sup> , reforestation/revegetation endeavours (e.g., Feng et al., 2016; Sonntag et al., 2016; Bright et al., 2017) <sup>[[#fn:r1300|1300]]</sup> and changes in land management (e.g., Luyssaert et al., 2014; Hirsch et al., 2017) <sup>[[#fn:r1301|1301]]</sup> that can involve double cropping (e.g., Jeong et al., 2014; Mueller et al., 2015; Seifert and Lobell, 2015) <sup>[[#fn:r1302|1302]]</sup> , irrigation (e.g., Lobell et al., 2009; Sacks et al., 2009; Cook et al., 2011; Qian et al., 2013; de Vrese et al., 2016; Pryor et al., 2016; Thiery et al., 2017) <sup>[[#fn:r1303|1303]]</sup> , no-till farming and conservation agriculture (e.g., Lobell et al., 2006; Davin et al., 2014) <sup>[[#fn:r1304|1304]]</sup> , and wood harvesting (e.g., Lawrence et al., 2012) <sup>[[#fn:r1305|1305]]</sup> . Hence, the biophysical impacts of land-use changes are an important topic to assess in the context of low-emissions scenarios (e.g., van Vuuren et al., 2011b) <sup>[[#fn:r1306|1306]]</sup> , in particular for 1.5°C warming levels (see also Cross-Chapter Box 7 in this chapter).

The magnitude of the biophysical impacts is potentially large for temperature extremes. Indeed, changes induced both by modifications in moisture availability and irrigation and by changes in surface albedo tend to be larger (i.e., stronger cooling) for hot extremes than for mean temperatures (e.g., Seneviratne et al., 2013; Davin et al., 2014; Wilhelm et al., 2015; Hirsch et al., 2017; Thiery et al., 2017) <sup>[[#fn:r1307|1307]]</sup> . The reasons for reduced moisture availability are related to a strong contribution of moisture deficits to the occurrence of hot extremes in mid-latitude regions (Mueller and Seneviratne, 2012; Seneviratne et al., 2013) <sup>[[#fn:r1308|1308]]</sup> . In the case of surface albedo, cooling associated with higher albedo (e.g., in the case of no-till farming) is more effective at cooling hot days because of the higher incoming solar radiation for these days (Davin et al., 2014) <sup>[[#fn:r1309|1309]]</sup> . The overall effect of either irrigation or albedo has been found to be at the most in the order of about 1°C–2°C regionally for temperature extremes. This can be particularly important in the context of low-emissions scenarios because the overall effect is in this case of similar magnitude to the response to the greenhouse gas forcing (Figure 3.22; Hirsch et al., 2017; Seneviratne et al., 2018a, c) <sup>[[#fn:r1310|1310]]</sup> .

'' '' In addition to the biophysical feedbacks from land-use change and land management on climate, there are potential consequences for particular ecosystem services. This includes climate change-induced changes in crop yield (e.g., Schlenker and Roberts, 2009; van der Velde et al., 2012; Asseng et al., 2013, 2015; Butler and Huybers, 2013; Lobell et al., 2014) <sup>[[#fn:r1311|1311]]</sup> which may be further exacerbated by competing demands for arable land between reforestation mitigation activities, crop growth for BECCS (Chapter 2), increasing food production to support larger populations, and urban expansion (see review by Smith et al., 2010) <sup>[[#fn:r1312|1312]]</sup> . In particular, some land management practices may have further implications for food security, for instance throughincreases or decreases in yield when tillage is ceased in some regions (Pittelkow et al., 2014) <sup>[[#fn:r1313|1313]]</sup> .

We note that the biophysical impacts of land use in the context of mitigation pathways constitute an emerging research topic. This topic, as well as the overall role of land-use change in climate change projections and socio-economic pathways, will be addressed in depth in the upcoming IPCC Special Report on Climate Change and Land Use due in 2019.

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'''Figure 3.22'''

<span id="regional-temperature-scaling-with-carbon-dioxide-co-2-concentration-ppm-from-1850-to-2099-for-two-different-regions-defined-in-the-special-report-on-managing-the-risks-of-extreme-events-and-disasters-to-advance-climate-change-adaptation-srex-for-central-europe-ceu-a-and-central-north-america-cna-b."></span>
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'''Regional temperature scaling with carbon dioxide (CO <sub>2</sub> ) concentration (ppm) from 1850 to 2099 for two different regions defined in the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) for central Europe (CEU) (a) and central North America (CNA) (b).'''
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[[File:1af916f9bc505370d0033b90a956974b Figure_3.22-1024x522.png]]

Solid lines correspond to the regional average annual maximum daytime temperature (TXx) anomaly, and dashed lines correspond to the global mean temperature anomaly, where all temperature anomalies are relative to 1850–1870 and units are degrees Celsius. The black line in all panels denotes the three-member control ensemble mean, with the grey shaded regions corresponding to the ensemble range. The coloured lines represent the three-member ensemble means of the experiments corresponding to albedo +0.02 (cyan), albedo +0.04 (purple), albedo + 0.08 (orange), albedo +0.10 (red), irrigation (blue), and irrigation with albedo +0.10 (green). Adapted from Hirsch et al. (2017) <sup>[[#fn:r1314|1314]]</sup> .

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