Editing IPCC:AR6/SRCCL/Chapter-6 (section)

=== 6.1.4 Challenges represented in future scenarios ===

<div id="section-6-1-4-challenges-represented-in-future-scenarios-block-1"></div>

In this section, the evolution of several challenges (climate change, mitigation, adaptation, desertification, land degradation, food insecurity, biodiversity and water) in the future are assessed, focusing on global analyses. The effect of response options on these land challenges in the future is discussed in Section 6.4.4. Where possible, studies quantifying these challenges in the Shared Socio-economic Pathways (SSPs) (O’Neill et al. 2014 <sup>[[#fn:r74|74]]</sup> ) (Chapter 1, Cross- Chapter Box 1, and Cross-Chapter Box 9 in this chapter), should be used to assess which future scenarios could experience multiple challenges in the future.

'''Climate change:''' Without any additional efforts to mitigate, global mean temperature rise is expected to increase by anywhere from 2°C to 7.8°C in 2100 relative to the 1850–1900 reference period (Clarke et al. 2014 <sup>[[#fn:r75|75]]</sup> ; Chapter 2). The level of warming varies, depending on the climate model (Collins et al. 2013 <sup>[[#fn:r76|76]]</sup> ), uncertainties in the Earth system (Clarke et al. 2014 <sup>[[#fn:r78|78]]</sup> ), and socio-economic/ technological assumptions (Clarke et al. 2014 <sup>[[#fn:r77|77]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r79|79]]</sup> ). Warming over land is 1.2 to 1.4 times higher than global mean temperature rise; warming in the Arctic region is 2.4 to 2.6 times higher than warming in the tropics (Collins et al. 2013 <sup>[[#fn:r80|80]]</sup> ). Increases in global mean temperature are accompanied by increases in global precipitation; however, the effect varies across regions, with some regions projected to see increases in precipitation and others to see decreases (Collins et al. 2013 <sup>[[#fn:r81|81]]</sup> ) (Chapter 2). Additionally, climate change also has implications for extreme events (e.g., drought, heat waves, etc.), freshwater availability, and other aspects of the terrestrial system (Chapter 2).

'''Mitigation:''' Challenges to mitigation depend on the underlying emissions and ‘mitigative capacity’, including technology availability, policy institutions, and financial resources (O’Neill et al. 2014 <sup>[[#fn:r82|82]]</sup> ). Challenges to mitigation are high in SSP3 and SSP5, medium in SSP2, and low in SSP1 and SSP4 (O’Neill et al. 2014, 2017; Riahi et al. 2017 <sup>[[#fn:r83|83]]</sup> ).

'''Adaptation:''' Challenges to adaptation depend on climate risk and adaptive capacity, including technology availability, effectiveness of institutions, and financial resources (O’Neill et al. 2014 <sup>[[#fn:r84|84]]</sup> ). Challenges to adaptation are high in SSP3 and SSP4, medium in SSP2, and low in SSP1 and SSP5 (O’Neill et al. 2014, 2017; Riahi et al. 2017 <sup>[[#fn:r85|85]]</sup> ).

'''Desertification:''' The combination of climate and land-use changes can lead to decreases in soil cover in drylands (Chapter 3). Population living in drylands is expected to increase by 43% in the SSP2-Baseline, due to both population increases and an expansion of dryland area (UNCCD 2017 <sup>[[#fn:r86|86]]</sup> ).

'''Land degradation:''' Future changes in land use and climate have implications for land degradation, including impacts on soil erosion, vegetation, fire, and coastal erosion (Chapter 4; IPBES 2018 <sup>[[#fn:r87|87]]</sup> ). For example, soil organic carbon is expected to decline by 99 GtCO <sub>2</sub> e in 2050 in an SSP2-Baseline scenario, due to both land management and expansion in agricultural area (Ten Brink et al. 2018 <sup>[[#fn:r88|88]]</sup> ).

'''Food insecurity:''' Food insecurity in future scenarios varies significantly, depending on socio-economic development and study. For example, the population at risk of hunger ranges from 0 to 800 million in 2050 (Hasegawa et al. 2015a <sup>[[#fn:r89|89]]</sup> ; Ringler et al. 2016 <sup>[[#fn:r90|90]]</sup> ; Fujimori et al. 2018 <sup>[[#fn:r91|91]]</sup> ; Hasegawa et al. 2018 <sup>[[#fn:r92|92]]</sup> ; Fujimori et al. 2019 <sup>[[#fn:r93|93]]</sup> ; Baldos and Hertel 2015 <sup>[[#fn:r94|94]]</sup> ) and 0–600 million in 2100 (Hasegawa et al. 2015a). Food prices in 2100 in non-mitigation scenarios range from 0.9 to about two times their 2005 values (Hasegawa et al. 2015a; Calvin et al. 2014 <sup>[[#fn:r95|95]]</sup> ; Popp et al. 2017 <sup>[[#fn:r96|96]]</sup> ). Food insecurity depends on both income and food prices (Fujimori et al. 2018 <sup>[[#fn:r97|97]]</sup> ). Higher income (e.g., SSP1, SSP5), higher yields (e.g., SSP1, SSP5), and less meat intensive diets (e.g., SSP1) tend to result in reduced food insecurity (Hasegawa et al. 2018 <sup>[[#fn:r98|98]]</sup> ; Fujimori et al. 2018 <sup>[[#fn:r99|99]]</sup> ).

'''Biodiversity:''' Future species extinction rates vary from modest declines to 100-fold increases from 20th century rates, depending on the species (e.g., plants, vertebrates, invertebrates, birds, fish, corals), the degree of land-use change, the level of climate change, and assumptions about migration (Pereira et al. 2010 <sup>[[#fn:r100|100]]</sup> ). Mean species abundance (MSA) is also estimated to decline in the future by 10–20% in 2050 (Van Vuuren et al. 2015; Pereira et al. 2010 <sup>[[#fn:r101|101]]</sup> ). Scenarios with greater cropland expansion lead to larger declines in MSA (UNCCD 2017 <sup>[[#fn:r102|102]]</sup> ) and species richness (Newbold et al. 2015 <sup>[[#fn:r103|103]]</sup> ).

'''Water stress:''' Changes in water supply (due to climate change) and water demand (due to socio-economic development) in the future have implications for water stress. Water withdrawals for irrigation increase from about 2500 km <sup>3</sup> yr <sup>–1</sup> in 2005 to between 2900 and 9000 km <sup>3</sup> yr <sup>–1</sup> at the end of the century (Chaturvedi et al. 2013 <sup>[[#fn:r104|104]]</sup> ; Wada and Bierkens 2014 <sup>[[#fn:r105|105]]</sup> ; Hejazi et al. 2014a <sup>[[#fn:r106|106]]</sup> ; Kim et al. 2016 <sup>[[#fn:r107|107]]</sup> ; Graham et al. 2018 <sup>[[#fn:r108|108]]</sup> ; Bonsch et al. 2015 <sup>[[#fn:r109|109]]</sup> ); total water withdrawals at the end of the century range from 5000 to 13,000 km <sup>3</sup> yr <sup>–1</sup> (Wada and Bierkens 2014 <sup>[[#fn:r110|110]]</sup> ; Hejazi et al. 2014a <sup>[[#fn:r111|111]]</sup> ; Kim et al. 2016 <sup>[[#fn:r112|112]]</sup> ; Graham et al. 2018 <sup>[[#fn:r113|113]]</sup> ). The magnitude of change in both irrigation and total water withdrawals depend on population, income, and technology (Hejazi et al. 2014a <sup>[[#fn:r114|114]]</sup> ; Graham et al. 2018 <sup>[[#fn:r115|115]]</sup> ). The combined effect of changes in water supply and water demand will lead to an increase of between 1 billion and 6 billion people living in water- stressed areas (Schlosser et al. 2014 <sup>[[#fn:r116|116]]</sup> ; Hanasaki et al. 2013 <sup>[[#fn:r117|117]]</sup> ; Hejazi et al. 2014b <sup>[[#fn:r118|118]]</sup> ). Changes in water quality are not assessed here but could be important (Liu et al. 2017 <sup>[[#fn:r119|119]]</sup> ).

'''Scenarios with multiple challenges:''' Table 6.2 summarises the challenges across the five SSP Baseline scenarios.

<div id="section-6-1-4-challenges-represented-in-future-scenarios-block-2"></div>

<span id="table-6.2"></span>
<!-- START TABLE -->
'''Table 6.2'''

<span id="assessment-of-future-challenges-to-climate-change-mitigation-adaptation-desertification-land-degradation-food-insecurity-water-stress-and-biodiversity-in-the-ssp-baseline-scenarios."></span>
'''Assessment of future challenges to climate change, mitigation, adaptation, desertification, land degradation, food insecurity, water stress, and biodiversity in the SSP Baseline scenarios.'''

<!-- TABLE -->
{| class="wikitable"
|-

SSP

Summary of challenges

|-

SSP1

SSP1 (Van Vuuren et al. 2017b) has low challenges to mitigation and adaptation. The resulting Baseline scenario includes:<br />
– continued, but moderate, ''climate change'' : global mean temperature increases by 3 to 3.5°C in 2100 (Huppmann et al. 2018 <sup>[[#fn:r120|120]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r121|121]]</sup> )<br />
– low levels of ''food insecurity'' : malnourishment is eliminated by 2050 (Hasegawa et al. 2015a)<br />
– declines in ''biodiversity'' : biodiversity loss increases from 34% in 2010 to 38% in 2100 (UNCCD 2017 <sup>[[#fn:r122|122]]</sup> )<br />
– high ''water stress'' : global water withdrawals decline slightly from the baseline in 2071–2100, but about 2.6 billion people live in water stressed areas (Hanasaki et al. 2013 <sup>[[#fn:r123|123]]</sup> ).

Additionally, this scenario is likely to have lower challenges related to desertification, land degradation, and biodiversity loss than SSP2 as it has lower population, lower land-use change and lower climate change (Riahi et al. 2017 <sup>[[#fn:r124|124]]</sup> ).

|-

SSP2

SSP2 (Fricko et al. 2017 <sup>[[#fn:r125|125]]</sup> ) is a scenario with medium challenges to mitigation and medium challenges to adaptation. The resulting Baseline scenario includes: – continued ''climate change'' : global mean temperature increases by 3.8°C to 4.3°C in 2100 (Fricko et al. 2017 <sup>[[#fn:r126|126]]</sup> ; Huppmann et al. 2018 <sup>[[#fn:r127|127]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r128|128]]</sup> )<br />
– increased challenges related to ''desertification'' : the population living in drylands is expected to increase by 43% in 2050 (UNCCD 2017 <sup>[[#fn:r129|129]]</sup> )<br />
– increased ''land degradation'' : soil organic carbon is expected to decline by 99 GtCO <sub>2</sub> e in 2050 (Ten Brink et al. 2018)

– low levels of ''food insecurity'' : malnourishment is eliminated by 2100 (Hasegawa et al. 2015a)<br />
– declines in biodiversity: ''biodiversity'' loss increases from 34% in 2010 to 43% in 2100 (UNCCD 2017 <sup>[[#fn:r130|130]]</sup> )<br />
– high ''water stress'' : global water withdrawals nearly doubles from the baseline in 2071–2100, with about 4 billion people living in water stressed areas (Hanasaki et al. 2013 <sup>[[#fn:r131|131]]</sup> ).

|-

SSP3

SSP3 (Fujimori et al. 2017 <sup>[[#fn:r132|132]]</sup> ) is a scenario with high challenges to mitigation and high challenges to adaptation. The resulting Baseline scenario includes: – continued ''climate change'' : global mean temperature increases by 4°C to 4.8°C in 2100 (Huppmann et al. 2018 <sup>[[#fn:r133|133]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r134|134]]</sup> )<br />
– high levels of ''food insecurity'' : about 600 million malnourished in 2100 (Hasegawa et al. 2015a)<br />
– declines in ''biodiversity'' : biodiversity loss increases from 34% in 2010 to 46% in 2100 (UNCCD 2017 <sup>[[#fn:r135|135]]</sup> )

– high ''water stress'' : global water withdrawals more than double from the baseline in 2071–2100, with about 5.5 billion people living in water stressed areas (Hanasaki et al. 2013 <sup>[[#fn:r136|136]]</sup> ).

Additionally, this scenario is likely to have higher challenges to desertification, land degradation, and biodiversity loss than SSP2 as it has higher population, higher land-use change and higher climate change (Riahi et al. 2017 <sup>[[#fn:r137|137]]</sup> ).

|-

SSP4

SSP4 (Calvin et al. 2017 <sup>[[#fn:r138|138]]</sup> ) has high challenges to adaptation but low challenges to mitigation. The resulting Baseline scenario includes:<br />
– continued ''climate change'' : global mean temperature increases by 3.4°C to 3.8°C in 2100 (Calvin et al. 2017 <sup>[[#fn:r139|139]]</sup> ; Huppmann et al. 2018 <sup>[[#fn:r140|140]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r141|141]]</sup> ) – high levels of ''food insecurity'' : about 400 million malnourished in 2100 (Hasegawa et al. 2015a)<br />
– high ''water stress'' : about 3.5 billion people live in water stressed areas in 2100 (Hanasaki et al. 2013 <sup>[[#fn:r142|142]]</sup> ).

Additionally, this scenario is likely to have similar effects on biodiversity loss as SSP2 as it has similar land-use change and similar climate change (Riahi et al. 2017 <sup>[[#fn:r143|143]]</sup> ).

|-

SSP5

SSP5 (Kriegler et al. 2017 <sup>[[#fn:r144|144]]</sup> ) has high challenges to mitigation but low challenges to adaptation. The resulting Baseline scenario includes:<br />
– continued climate change: global mean temperature increases by 4.6°C to 5.4°C in 2100 (Kriegler et al. 2017 <sup>[[#fn:r145|145]]</sup> ; Huppmann et al. 2018 <sup>[[#fn:r146|146]]</sup> ; Riahi et al. 2017 <sup>[[#fn:r147|147]]</sup> )<br />
– low levels of ''food insecurity'' : malnourishment is eliminated by 2050 (Hasegawa et al. 2015a)<br />
– increased water use and water scarcity: global water withdrawals increase by about 80% in 2071–2100, with nearly 50% of the population living in ''water stressed'' areas

(Hanasaki et al. 2013 <sup>[[#fn:r148|148]]</sup> ).<br />
Additionally, this scenario is likely to have higher effects on biodiversity loss as SSP2 as it has similar land-use change and higher climate change (Riahi et al. 2017 <sup>[[#fn:r149|149]]</sup> ).

|}
<!-- END TABLE -->

<span id="response-options-co-benefits-and-adverse-side-effects-across-the-land-challenges"></span>