Editing IPCC:AR6/WGIII/Chapter-9 (section)

=== Box 9.2 | Scenarios Used for the Purpose of This Chapter ===

<div id="h2-6-siblings" class="h2-siblings"></div>

Three out of the four scenarios selected, and their related baselines, are based on top-down modelling and were submitted to AR6 scenario database, which includes in total 931 scenarios with a building module (Annex III; see also Boxes 3.1 and 3.2, and Cross-Chapter Box 3 in Chapter 3). A fourth scenario, not included in AR6 scenario database, and based on a bottom-up modelling approach was added.

The main features of these scenarios are shortly described below while the underlying modelling approaches are described in Annex III. Each scenario is assessed compared to its baseline scenario:

Box 9.2

International Energy Agency (IEA) scenarios:

'''2021 Net Zero Emissions by 2050 Scenario (NZE)''' is a normative scenario, which sets out a narrow but achievable pathway for the global energy sector to achieve net zero CO 2 emissions by 2050 ( [[#IEA--2021a|IEA 2021a]] ).

'''2020 Sustainable Development Scenario (SDS)''' '','' which integrates the impact of COVID-19 on health outcomes and economies. It is also a normative scenario, working backwards from climate, clean air, and energy access goals. SDS examines what actions would be necessary to achieve these goals. The near-term detail is drawn from the IEA Sustainable Recovery Plan, which boosts economies and employment while building cleaner and more resilient energy systems ( [[#IEA--2020c|IEA 2020c]] ).

Analysis of the IEA scenarios above was conducted compared to the 2019 Current Policies Scenario, which shows what happens if the world continues along its present path ( [[#IEA--2020c|IEA 2020c]] ), and considered as a baseline scenario.

'''IMAGE-Lifestyle-Renewable''' '''(LiRE)''' scenario is based on an updated version of the SSP2 baseline, while also meeting the RCP2.6 radiative forcing target using carbon prices, together with the increased adoption of additional lifestyle changes, by limiting the growth in the floor area per capita in Developed Countries as well as the use of appliances. Regarding energy supply, IMAGE-LiRE assumes increased electrification and increased share of renewable in the energy mix (Detlef Van [[#Vuuren--2021|Vuuren et al. 2021]] ).

'''Resource Efficiency and Climate Change-Low Energy Demand (RECC-LED) scenario''' is produced by a global bottom-up model, which assesses contributions of resource efficiency to climate change mitigation. RECC-LED estimates the energy and material flows associated with housing stock growth, driven by population and the floor area per capita ( [[#Pauliuk--2021|Pauliuk et al. 2021]] ). This scenario is informed by the Low Energy Demand Scenario (LED), which seeks convergence between developed and developing countries in the access to decent living standard ( [[#Grubler--2018|Grubler et al. 2018]] ).

For consistency between the four scenarios, aggregation of regions in this chapter differs from the one of the IPCC. Europe and Eurasia have been grouped into one single region.

The IEA-NZE scenario projects emissions from the global building stock to be lowered to 29 MtCO 2 by 2050 against 1.7 GtCO 2 in the IEA-SDS and 3.7 GtCO 2 in IMAGE-LiRE Scenario. These projections can be compared to IEA-CPS in which global emissions from buildings were projected to be at 13.5 GtCO 2 in 2050, which is equivalent to the 2018 emissions level (Figure 9.3a). By 2050, direct emissions from residential buildings are projected to be lowered to 108 MtCO 2 in the IEA-NZE, this is four times less than the projected direct emissions in RECC-LED scenario, six times less than those under the IEA-SDS and eleven times less than those in the IMAGE-LiRE scenario.

In the IEA-NZE scenario, indirect emissions are projected to be below zero by 2050 for both residential and non-residential buildings, while residual indirect emissions from residential buildings are projected to be 125 MtCO 2 in RECC-LED, 634 MtCO 2 in IEA-SDS, and 842 GtCO 2 in IMAGE-LiRE. Residual indirect emissions from non-residential buildings are projected to be at 1.7 GtCO 2 in IEA SDS and double of this in IMAGE-LiRE scenario (Figure 9.3a). Compared to IEA-SDS, the highest decrease of emissions in IEA-NZE is expected to occur after 2030. Direct emissions from residential buildings in IEA-NZE are projected to be, by 2030, at 1.37 GtCO 2 , against 1.7 GtCO 2 in the three other scenarios. The highest cut in emissions in IEA-NZE and in IMAGE-LiRE occur through the decarbonisation of energy supply.

At regional level, by 2050, the lowest emissions are projected to occur in developed Asia and Pacific, with 6.73 MtCO 2 under RECC-LED scenario and 12.4 MtCO 2 under the IEA-SDS, and the highest emissions are projected to occur in Europe and Eurasia in all three scenarios, with 152 MtCO 2 in IEA-SDS, 199 MtCO 2 in RECC-LED scenario and 381 MtCO 2 in IMAGE-LiRE scenario. Emissions in Africa are projected to decrease to 10 MtCO 2 in RECC-LED, this is nine time less than those of 2019, while they are projected to increase by 25% in IEA-SDS compared to those of 2019. Compared to IEA-SDS and IMAGE-LiRE, RECC-LED projects the highest decreases, over the period 2020–2030, of direct emissions in residential buildings in all regions, up to 45% in Australia, Japan and New Zealand, and Eastern Asia and the highest decreases of indirect emissions, ranging from 52% in Eastern Asia to 86% in Latin America and Caribbean. Over the same period, the IEA-SDS projects the highest decreases of indirect emissions to occur in Australia, Japan and New Zealand, and North America. IMAGE-LiRE projects the lowest decreases of emissions over the same decade in almost all regions (Figure 9.3b).

Emissions per capita from residential buildings at a global level reached 0.85 tCO 2 per person in 2019. The four scenarios assessed project a decrease of the global per capita emissions by 2050, ranging from 0 tCO 2 in IEA-NZE 0.21 tCO 2 per person in IMAGE-LiRE, a 75% lower than those of 2019 (Figure 9.4a). There are great differences in the projected per capita emissions under each scenario different scenarios across the regions (Figure 9.4b). Compared to IEA-SDS and IMAGE-LiRE scenarios, RECC-LED projects the lowest emissions per capita in all regions by 2050. Emissions per capita in Europe and Eurasia are projected to be the highest in all scenarios by 2050, ranging from 0.26 tCO 2 in RECC-LED and 0.31 tCO 2 in IEA-SDS to 0.65 tCO 2 in IMAGE-LiRE.

<div id="_idContainer020" class="Basic-Text-Frame"></div>

[[File:8504c76bf294ed20c92aa0bf4211f7b0 IPCC_AR6_WGIII_Figure_9_5.png]]

'''Figure 9.4 | Per capita emissions: historical based on IEA data and future emissions based on two IEA scenarios (sustainable development, and net zero emissions), IMAGE Lifestyle-Renewable scenario and Resource Efficiency and Climate Change-Low Energy Demand scenario (RECC-LED).''' RECC-LED data include only space heating and cooling and water heating in residential buildings. The IEA current policies scenario is included as a baseline scenario (IEA current policies scenario).

<div id="9.3.2" class="h2-container"></div>

<span id="drivers-of-co-2-emissions-and-their-climate-impact"></span>