Editing IPCC:AR6/SR15/Chapter-2 (section)

== 2.3.1.1 Socio-economic drivers and the demand for energy and land in 1.5°C pathways ==

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There is deep uncertainty about the ways humankind will use energy and land in the 21st century. These ways are intricately linked to future population levels, secular trends in economic growth and income convergence, behavioural change and technological progress. These dimensions have been recently explored in the context of the SSPs (Kriegler et al., 2012; O’Neill et al., 2014) <sup>[[#fn:r139|139]]</sup> , which provide narratives (O’Neill et al., 2017) <sup>[[#fn:r140|140]]</sup> and quantifications (Crespo Cuaresma, 2017; Dellink et al., 2017; KC and Lutz, 2017; Leimbach et al., 2017; Riahi et al., 2017) <sup>[[#fn:r141|141]]</sup> of different world futures across which scenario dimensions are varied to explore differential challenges to adaptation and mitigation (Cross-Chapter Box 1 in Chapter 1). This framework is increasingly adopted by IAMs to systematically explore the impact of socio-economic assumptions on mitigation pathways (Riahi et al., 2017) <sup>[[#fn:r142|142]]</sup> , including 1.5°C-consistent pathways (Rogelj et al., 2018) <sup>[[#fn:r143|143]]</sup> . The narratives describe five worlds (SSP1–5) with different socio-economic predispositions to mitigate and adapt to climate change (Table 2.3). As a result, population and economic growth projections can vary strongly across integrated scenarios, including available 1.5°C-consistent pathways (Figure. 2.4). For example, based on alternative future fertility, mortality, migration and educational assumptions, population projections vary between 8.5 and 10.0 billion people by 2050 and between 6.9 and 12.6 billion people by 2100 across the SSPs. An important factor for these differences is future female educational attainment, with higher attainment leading to lower fertility rates and therefore decreased population growth up to a level of 1 billion people by 2050 (Lutz and KC, 2011; Snopkowski et al., 2016; KC and Lutz, 2017) <sup>[[#fn:r144|144]]</sup> . Consistent with population development, GDP per capita also varies strongly in SSP baselines, ranging from about 20 to more than 50 thousand USD2010 per capita in 2050 (in purchasing power parity values, PPP), in part driven by assumptions on human development, technological progress and development convergence between and within regions (Crespo Cuaresma, 2017; Dellink et al., 2017; Leimbach et al., 2017) <sup>[[#fn:r145|145]]</sup> . Importantly, none of the GDP projections in the mitigation pathway literature assessed in this chapter included the feedback of climate damages on economic growth (Hsiang et al., 2017) <sup>[[#fn:r146|146]]</sup> .

Baseline projections for energy-related GHG emissions are sensitive to economic growth assumptions, while baseline projections for land-use emissions are more directly affected by population growth (assuming unchanged land productivity and per capita demand for agricultural products) (Kriegler et al., 2016) <sup>[[#fn:r147|147]]</sup> . SSP-based modelling studies of mitigation pathways have identified high challenges to mitigation for worlds with a focus on domestic issues and regional security combined with high population growth (SSP3), and for worlds with rapidly growing resource and fossil-fuel intensive consumption (SSP5) (Riahi et al., 2017) <sup>[[#fn:r148|148]]</sup> . No model could identify a 2°C-consistent pathway for SSP3, and high mitigation costs were found for SSP5. This picture translates to 1.5°C-consistent pathways that have to remain within even tighter emissions constraints (Rogelj et al., 2018) <sup>[[#fn:r149|149]]</sup> . No model found a 1.5°C-consistent pathway for SSP3 and some models could not identify 1.5°C-consistent pathways for SSP5 (2 of 4 models, compared to 1 of 4 models for 2°C-consistent pathways). The modelling analysis also found that the effective control of land-use emissions becomes even more critical in 1.5°C-consistent pathways. Due to high inequality levels in SSP4, land use can be less well managed. This caused 2 of 3 models to no longer find an SSP4-based 1.5°C-consistent pathway even though they identified SSP4-based 2°C-consistent pathways at relatively moderate mitigation costs (Riahi et al., 2017) <sup>[[#fn:r150|150]]</sup> . Rogelj et al. (2018) <sup>[[#fn:r151|151]]</sup> further reported that all six participating models identified 1.5°C-consistent pathways in a sustainability oriented world (SSP1) and four of six models found 1.5°C-consistent pathways for middle-of-the-road developments (SSP2). These results show that 1.5°C-consistent pathways can be identified under a broad range of assumptions, but that lack of global cooperation (SSP3), high inequality (SSP4) and/or high population growth (SSP3) that limit the ability to control land use emissions, and rapidly growing resource-intensive consumption (SSP5) are key impediments.

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====== Table 2.3 ======

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==== Key Characteristics of the Five Shared Socio-Economic Pathways (SSPs) (O’Neill et al., 2017) ====

{| class="wikitable"
|-
! rowspan="2"| Socio-Economic Challenges to Mitigation
! colspan="3"| Socio-Economic Challenges to Adaptation
|-
! Low
! Medium
! High
|-
! High
| SSP5: Fossil-fuelled development
* low population
* very high economic growth per capita
* high human development
* high technological progress
* ample fossil fuel resources
* very resource intensive lifestyles
* high energy and food demand per capita
* economic convergence and global cooperation

|
| SSP3: Regional rivalry
* high population
* low economic growth per capita
* low human development
* low technological progress
* resource-intensive lifestyles
* resource-constrained energy and food demand per capita
* focus on regional food and energy security
* regionalization and lack of global cooperation

|-
! Medium
|
| SSP2: Middle of the road
* medium population
* medium and uneven economic growth
* medium and uneven human development
* medium and uneven technological progress
* resource-intensive lifestyles
* medium and uneven energy and food demand per capita
* limited global cooperation and economic convergence

|
|-
! Low
| SSP1: Sustainable development
* low population
* high economic growth per capita
* high human development
* high technological progress
* environmentally oriented technological and behavioural change
* resource-efficient lifestyles
* low energy and food demand per capita
* economic convergence and global cooperation

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| SSP4: Inequality
* Medium to high population
* Unequal low to medium economic growth per capita
* low to medium human development
* unequal technological progress: high in globalized
* high-tech sectors, slow in domestic sectors
* unequal lifestyles and energy /food consumption: resource intensity depending on income
* Globally connected elite, disconnected domestic work forces

|}

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====== Figure 2.4 ======

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==== Range of assumptions about socio-economic drivers and projections for energy and food demand in the pathways available to this assessment. 1.5°C-consistent pathways are blue, other pathways grey. ====

[[File:ddd5af9bf56e5ef2f3f7a8bd1375919c Figure-2.4-1024x768.jpg|thumb|400x300px]]

Trajectories for the illustrative 1.5°C-consistent archetypes used in this Chapter (LED, S1, S2, S5; referred to as P1, P2, P3, and P4 in the Summary for Policymakers.) are highlighted. S1 is a sustainability oriented scenario, S2 is a middle-of-the-road scenario, and S5 is a fossil-fuel intensive and high energy demand scenario. LED is a scenario with particularly low energy demand. Population assumptions in S2 and LED are identical. Panels show (a) world population, (b) gross world product in purchasing power parity values, (c) final energy demand, and (d) food demand.

Original Creation for this Report using IAMC 1.5°C Scenario Data hosted by IIASA

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Figure 2.4 compares the range of underlying socio-economic developments as well as energy and food demand in available 1.5°C-consistent pathways with the full set of published scenarios that were submitted to this assessment. While 1.5°C-consistent pathways broadly cover the full range of population and economic growth developments (except for the high population development in SSP3-based scenarios), they tend to cluster on the lower end for energy and food demand. They still encompass, however, a wide range of developments from decreasing to increasing demand levels relative to today. For the purpose of this assessment, a set of four illustrative 1.5°C-consistent pathway archetypes were selected to show the variety of underlying assumptions and characteristics (Figure 2.4). They comprise three 1.5°C-consistent pathways based on the SSPs (Rogelj et al., 2018) <sup>[[#fn:r153|153]]</sup> : a sustainability oriented scenario (S1 based on SSP1) developed with the AIM model (Fujimori, 2017) <sup>[[#fn:r154|154]]</sup> , a fossil-fuel intensive and high energy demand scenario (S5, based on SSP5) developed with the REMIND-MAgPIE model (Kriegler et al., 2017) <sup>[[#fn:r155|155]]</sup> , and a middle-of-the-road scenario (S2, based on SSP2) developed with the MESSAGE-GLOBIOM model (Fricko et al., 2017) <sup>[[#fn:r156|156]]</sup> . In addition, we include a scenario with low energy demand (LED) (Grubler et al., 2018) <sup>[[#fn:r157|157]]</sup> , which reflects recent literature with a stronger focus on demand-side measures (Bertram et al., 2018; Grubler et al., 2018; Liu et al., 2018; van Vuuren et al., 2018) <sup>[[#fn:r158|158]]</sup> . Pathways LED, S1, S2, and S5 are referred to as P1, P2, P3, and P4 in the Summary for Policymakers.

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