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

==== 6.7.1.1 Energy System Emissions ====

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Without additional efforts to reduce emissions, it is very unlikely that energy system CO 2 emissions will decrease sufficiently to limit warming to well below 2°C ( ''high confidence'' ). Scenarios assuming improvements in technology but no additional climate policies beyond those in place today provide a benchmark for comparison against energy-related CO 2 emissions in mitigation scenarios (Figure 6.26). Emissions in these reference scenarios increase through 2050 but span a broad range ( [[#Riahi--2017|Riahi et al. 2017]] ; [[#Wei--2018|Wei et al. 2018]] ) (Chapter 3, Figure 3.16). The highest emission levels are about four times current emissions; the lowest are modestly below today’s emissions. Emissions in these scenarios increase in most regions, but they diverge significantly across regions ( [[#Bauer--2017|Bauer et al. 2017]] ). Asia and the Middle East and Africa account for the majority of increased emissions across these scenarios (Figure 6.27). While it is unlikely that there will be no new climate policies in the future, these scenarios nonetheless support the conclusion that the energy sector will not be decarbonised without explicit policy actions to reduce emissions.

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'''Figure 6.26 | Projected energy sector GHG emissions for t''' '''he 1.''' '''5°C scenarios (without and with overshoot), and likely below 2°C scenarios (without and with delayed policy action) during 2020–2050''' (Source: AR6 Scenarios Database). Boxes indicate 25th and 75th percentiles, while whiskers indicate 5th and 95th percentiles. GHG emissions are inclusive of energy sector CO 2 , CH 4 , N 2 O emissions and 80% of global HFC emissions. Number of model-scenario combinations in AR6 Scenarios Database: limit warming to 1.5°C (&gt;50%) with no or limited overshoot: 77; return warming to 1.5°C (&gt;50%) after a high overshoot: 110; limit warming to 2(C (&gt;67%) with action starting in 2020: 164; limit warming to 2°C (&gt;67%) with NDCs until 2030: 97.

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'''Figure 6.27 | Net regional (R6) CO''' 2 '''emissions from energy across scenarios that limit/return''' '''warming to 1.''' '''5°C (&gt;50%) with no or limited/after a high overshoot, and scenarios that limit warming to 2°C (&gt;67%) with action starting in 2020 or with NDCs until 2030, during 2020–2050''' (Source: AR6 Scenarios Database). Boxes indicate 25th and 75th percentiles, while whiskers indicate 5th and 95th percentiles. Most mitigation scenarios are based on a cost-minimising framework that does not consider historical responsibility or other equity approaches.

Warming cannot be limited to well below 2°C without rapid and deep reductions in energy system GHG emissions ( ''high confidence'' ). Energy sector CO 2 emissions fall by 87–97% (interquartile range) by 2050 in scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot and 60–79% in scenarios limiting warming to 2°C (&gt;67%) with action starting in 2020 (Figure 6.26). Energy sector GHG emissions fall by 85–95% (interquartile range) in scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot, and 62–78% in scenarios limiting warming to 2°C (&gt;67%) with action starting in 2020 (Figure 6.26). In 2030, in scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot, net CO 2 and GHG emissions fall by 35–51% and 38–52% respectively. Key characteristics of emissions pathways – the year of peak emissions, the year when net emissions reach zero, and the pace of emissions reductions – vary widely across countries and regions. These differences arise from differences in economic development, demographics, resource endowments, land use, and potential carbon sinks (Schaeffer, et al. 2020; Schreyer, et al. 2020; van Soest, Heleen et al. 2021) (Figure 6.27, Figure 6.28, Box 6.11). If countries do not move quickly to reduce emissions – if reductions are delayed – a more rapid energy transition will subsequently be required to limit warming to 2°C or lower ( [[#Rogelj--2015a|Rogelj et al. 2015a]] , 2018a; [[#IPCC--2018|IPCC 2018]] ).

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'''Figure 6.28 | The timing of net-zero emissions for full economy greenhouse gases (GHGs), energy sector CO''' 2 ''', and electricity sector CO''' 2 '''.''' Boxes indicate 25th and 75th percentiles, centre black line is the median, while whiskers indicate 1.5x the inter-quartile range. The vertical dashed lines represent the median point at which emissions in the scenarios have dropped by 95% (pink) and 97.5% (purple), respectively. Dots represent individual scenarios. The fraction indicates the number of scenarios reaching net-zero by 2100 out of the total sample. Source: AR6 Scenario Database.

The timing of net-zero energy system emissions varies substantially across scenarios. In scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot (2°C (&gt;67%)), the energy system reaches net-zero CO 2 emissions (interquartile range) from 2060 onwards (2080–). (Figure 6.28). However, net emissions reach near-zero more quickly. For example, in scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot (2°C (&gt;67%)) net energy system CO 2 emissions drop by 95% between 2056 and 2075 (2073 and 2093). Net full economy GHG emissions reach zero more slowly than net CO 2 emissions. In some scenarios, net energy system CO 2 and total GHG emissions do not reach zero this century, offset by CDR in other sectors.

The timing of emissions reductions will vary across the different parts of the energy sector (Figure 6.28). To decarbonise most cost-effectively, global net CO 2 emissions from electricity generation will likely reach zero before the rest of the energy sector ( ''medium confidence'' ). In scenarios limiting warming to 1.5°C (&gt;50%) with no or limited overshoot (2°C (&gt;67%)), net electricity sector CO 2 emissions (interquartile range) reach zero globally between 2044 and 2055 (2052 and 2078) (Figure 6.28). It is likely to be less costly to reduce net CO 2 emissions close to or below zero in the electricity sector than in other sectors, because there are relatively more low-emissions options in electricity. Sectors such as long-distance transport, air transport, and process heat are anticipated to face greater challenges to decarbonisation than the electricity sector ( [[#Clark--2014|Clark and Herzog 2014]] ; [[#Rogelj--2015b|Rogelj et al. 2015b]] , 2018b; [[#IPCC--2018|IPCC 2018]] ; [[#Luderer--2018|Luderer et al. 2018]] ).

In addition, there are potential options to remove CO 2 from the atmosphere in the electricity sector, notably BECCS, which would allow electricity sector emissions to drop below zero. Without CDR options, electricity sector emissions may not fall all the way to zero. If CDR is accomplished in other sectors and not in electricity, some fossil fuel plants may still lead to positive net electricity sector CO 2 emissions, even in net-zero economies ( [[#Bistline--2021b|Bistline and Blanford 2021b]] ; [[#Williams--2021a|Williams et al. 2021a]] ).

We lack sufficient understanding to pin down precise dates at which energy system CO 2 emissions in individual countries, regions, or sectors will reach net zero. Net-zero timing is based on many factors that are not known today or are bound up in development of key technologies, such as energy storage, bioenergy, or hydrogen. Some countries have low-carbon resource bases that could support deep emissions reductions, while others do not. Timing is also affected by the availability of CDR options, whether these options are in the energy sector or elsewhere, and the discount rate used to assess strategies ( [[#Bednar--2019|Bednar et al. 2019]] ; [[#Emmerling--2019|Emmerling et al. 2019]] ). Moreover, while many scenarios are designed to minimise global mitigation costs, many other frameworks exist for allocating mitigation effort across countries (van den Berg et al. 2019) (Chapter 4).

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