Socioeconomic factors and future challenges of the goal of limiting the increase in global average temperature to 1.5 °C

Abstract

The Paris Agreement has confirmed that the ultimate climate policy goal is to hold the increase in the global average temperature to well below 2 C above pre-industrial levels and to pursue efforts to limit the increase to 1.5 C. Moving the goal from 2 C to 1.5 C calls for much more concerted effort, and presents greater challenges and costs. This study uses an Asia-Pacific Integrated Model/Computable General Equilibrium (AIM/CGE) to evaluate the role of socioeconomic factors (e.g. technological cost and energy demand assumptions) in changing mitigation costs and achieving the 1.5C and 2 C goals, and to identify the channels through which socioeconomic factors affect mitigation costs. Four families of socioeconomic factors were examined, namely low-carbon energy-supply technologies, end-use energy-efficiency improvements, lifestyle changes and biomass-technology promotion (technology cost reduction and social acceptance promotion). The results show that technological improvement in low-carbon energy-supply technologies is the most important factor in reducing mitigation costs. Moreover, under the constraints of the 1.5 C goal, the relative effectiveness of other socioeconomic factors, such as energy efficiency improvement, lifestyle changes and biomassrelated technology promotion, becomes more important in decreasing mitigation cost in the 1.5 C scenarios than in the 2 C scenarios.

Numerical modeling of the global climate and carbon cycle system

“…Since the AR5, several new, integrated multimodel studies have appeared in the literature that explore specific characteristics of scenarios more stringent than the lowest scenario category assessed in AR5 than was assessed to limit warming below 2°C with greater that 66% likelihood (Rogelj et al, 2015b(Rogelj et al, , 2018Akimoto et al, 2017;Marcucci et al, 2017;Su et al, 2017;Bauer et al, 2018;Bertram et al, 2018;Grubler et al, 2018;Holz et al, 2018b;Kriegler et al, 2018a;Liu et al, 2018;Luderer et al, 2018;Strefler et al, 2018a; van Vuuren et al, 2018;Vrontisi et al, 2018;Zhang et al, 2018). Those scenarios explore 1.5°C-consistent pathways from multiple perspectives (see Supplementary Material 2.SM.1.3), examining sensitivity to assumptions regarding:…”

“…They comprise three 1.5°C-consistent pathways based on the SSPs (Rogelj et al, 2018): a sustainability oriented scenario (S1 based on SSP1) developed with the AIM model (Fujimori, 2017), a fossil-fuel intensive and high energy demand scenario (S5, based on SSP5) developed with the REMIND-MAgPIE model (Kriegler et al, 2017), and a middle-ofthe-road scenario (S2, based on SSP2) developed with the MESSAGE-GLOBIOM model (Fricko et al, 2017). In addition, we include a scenario with low energy demand (LED) (Grubler et al, 2018), 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). Pathways LED, S1, S2, and S5 are referred to as P1, P2, P3, and P4 in the Summary for Policymakers.…”

“…Several studies have either directly or indirectly explored the dependence of 1.5°C-consistent pathways on specific (sets of) mitigation and CDR technologies (Bauer et al, 2018;Grubler et al, 2018;Holz et al, 2018b;Kriegler et al, 2018a;Liu et al, 2018;Rogelj et al, 2018;Strefler et al, 2018b;van Vuuren et al, 2018). However, there are a few potentially disruptive technologies that are typically not yet well covered in IAMs and that have the potential to alter the shape of mitigation pathways beyond the ranges in the IAM-based literature.…”

“…1.5°C-consistent pathways are characterized by a rapid phase out of CO 2 emissions and deep emissions reductions in other GHGs and climate forcers ( Section 2.2.2 and 2.3.3). This is achieved by broad transformations in the energy; industry; transport; buildings; and agriculture, forestry and other land-use (AFOLU) sectors (Section 2.4) (Bauer et al, 2018;Grubler et al, 2018;Holz et al, 2018b;Kriegler et al, 2018b;Liu et al, 2018;Luderer et al, 2018;Rogelj et al, 2018;van Vuuren et al, 2018;Zhang et al, 2018). Here we assess 1.5°C-consistent pathways with and without overshoot during the 21st century.…”

“…We conclude that the role of BECCS as a dominant CDR measure in deep mitigation pathways has been reduced since the time of the AR5. This is related to three factors: a larger variation of underlying assumptions about socio-economic drivers (Riahi et al, 2017;Rogelj et al, 2018) and associated energy (Grubler et al, 2018) and food demand (van Vuuren et al, 2018); the incorporation of a larger portfolio of mitigation and CDR options (Marcucci et al, 2017;Grubler et al, 2018;Lehtilä and Koljonen, 2018;Liu et al, 2018;van Vuuren et al, 2018); and targeted analysis of deployment limits for (specific) CDR measures (Holz et al, 2018b;Kriegler et al, 2018a;Strefler et al, 2018b), including the availability of bioenergy (Bauer et al, 2018), CCS (Krey et al, 2014a;Grubler et al, 2018) and afforestation (Popp et al, 2014b(Popp et al, , 2017. As additional CDR measures are being built into IAMs, the prevalence of BECCS is expected to be further reduced.…”