Overall CO2 emissions and final energy use in 2050
The CO2 emissions in 2050 for the 26by30 + 80by50_Def scenario are around 280Mt-CO2 (237–336Mt-CO2). The supply side sees a sharp reduction to which the emissions are less than 100Mt-CO2 in all models. However, the demand sector still emits approximately 200Mt-CO2 (199–252Mt-CO2) (see Figure ESM 1.) showing that the demand-side reduction is crucial in achieving emissions reduction targets. The total amount of CO2 captured and stored is around 160Mt-CO2 (23–350Mt-CO2), of which around 40 Mt-CO2 (0–109Mt-CO2) is captured in the demand sector (the industry sector, including industrial processes).
Next, we present final energy (reported in lower heating value) by fuel types in 2010Footnote 2 and 2050 for the 26by30 + 80by50_Def scenario (Fig. 1). One common trend among the models is a drastic decrease in liquids, mostly oil products, by 4.1EJ to 5.5EJ compared to 2010 (the reduction rate ranges from 44 to 78%). A similar trend of decreasing consumption is observed in solids, which sees a decrease by about 1EJ in all models. Other energy carriers, electricity, hydrogen and gases, see different patterns depending on models.
All models show a substantial decrease in the final energy use from 2010 to 2050. The net final energy use decreases by 5EJ in AIM/Enduse and by 7EJ in IEEJ. Despite similar reduction in liquids and solids, the net final energy use only decreases around 4EJ in AIM/Hub, DNE21, and TIMES-Japan due to the increasing use of electricity, gas and hydrogen.
In AIM/Enduse, most fuels are reduced with only a slight increase in hydrogen and “other all (heat, solar, and other sources)”. In IEEJ, only a slight increase in hydrogen is seen and significant energy savings in all other fuels. In AIM/Hub, DNE21, and TIMES-Japan electricity, gas and hydrogen increase while fossil fuel consumption reduces. In AIM/Hub, a significant increase in electricity consumption is observed. In DNE21, electricity and gases increase. In TIMES-Japan, electricity, gases, and hydrogen significantly increase.
The electricity demand stays at a relatively the same level compared to the current consumption, 3.0–4.5EJ (840–1260TWh), with one exception of AIM/Hub which sees a sharp increase to 7.0EJ (1950TWh) in 2050.Footnote 3 In terms of the absolute electricity demand, both results of increasing and decreasing were seen among models, which is consistent with the findings of Sugiyama (2012). Despite the level of consumption staying relatively flat in 2050, the electrification rate increases in all models (AIM/Enduse: 37%; AIM/Hub: 66%; DNE21: 39%; IEEJ: 44%; TIMES: 43%) compared to around 26% in 2010 as the total final energy use decreases. The electrification rates increase at a pace of 0.03–0.45%/year from 2010 to 2030, but increase at a faster pace of 0.46–1.58%/year from 2030 to 2050.
With regards to other clean energy carriers, a notable increase in hydrogen is seen in IEEJ and TIMES-Japan models, providing around 10% of final energy in 2050 (AIM/Hub and DNE21 have no hydrogen option).
CO2 emissions and final energy use by sectors in 2050
The overall direct CO2 emissions reduction rate of the demand-side from 2010 to 2050 is approximately 70%, but the reduction rates by sectors vary across models as shown in Fig. 2. The CO2 emissions reduction rates are 50–84% in the industry sector including industrial processes, 36–82% in the residential sector, 34–100% in the commercial sector, and 54–93% in the transportation sector.
The CO2 emissions in the transportation sector are the smallest in AIM/Enduse while they are the largest in AIM/Hub. Both in IEEJ and TIMES-Japan, the largest emitting sector is the industry sector and the smallest is the commercial sector. However, in IEEJ, the CO2 emissions of the residential sector is about half of the transportation sector, but in TIMES-Japan, the residential sector and the transportation sector have almost the same CO2 emissions.
The variation among models is caused by the differences in final energy use changes in each sector from 2010 to 2050. Figure 3. shows the differences among models in the final energy use by fuels in industry, residential, commercial, and transportation sectors in 2010 and 2050. The industry sector continues to be the most consuming sector in all models despite the largest decrease in the final energy use among all sectors in most models. The transport sector goes through a rapid transition with a rapid decline in use of liquids (mostly oil products).
The final energy use in the industry sector in 2050 ranges between 3.3 and 5.7EJ, and the electricity consumption ranges between 0.8 and 2.5EJ. The share of final energy use by the industry sector in 2050 is 32–60%, close to half in three models. The industry sector transforms its energy composition largely dependent on liquids and solids (around 60% in all models) in 2010 to delivering half of its energy from electricity, gases and hydrogen in 2050. Although the largest reduction is seen in liquids, the consumption of liquids still stays high around 1.2EJ in all models. Solids are also reduced in all models, but most models still use around 0.6EJ in 2050.
The final energy use in the residential sector ranges between 1.2 and 2.4EJ of which gases and electricity make up most of the demand. The reduction in liquids demand is a major movement in the residential sector as the liquids demand decreases to less than 0.1EJ in three models, implying that oil water heater and stoves are virtually phased out in the residential sector (Oshiro and Fujimori 2020). Most models see a decrease in the final energy demand, but AIM/Hub sees an increase as the increase in electricity demand surpasses the decrease in liquids demand.
The final energy use in the commercial sector in 2050 is 1.3–2.4EJ, of which electricity is the major energy carrier. The use of liquids and gases are greatly reduced and almost no longer consumed (0–0.02EJ for liquids, 0–0.2EJ for gases) except for AIM/Enduse which has a relatively large CO2 emissions in the commercial sector. This implies that nearly all oil and gas appliances (mainly cooking, water heater, and space heating) needs to be phased out in this sector to reach emissions reduction targets.
The transportation sector sees a rapid transformation from heavily liquids dependent energy composition to a more mixed composition. Other than AIM/Hub, which does not model hydrogen, models see an increase in both electricity and hydrogen. The electricity consumption increases to 0.3–0.6EJ, whereas the hydrogen consumption increases to 0.1–0.6EJ. Since most of the energy use in the transportation sector was oil products in 2010, liquids consumption decreases by 1.3–2.5EJ. The replacing technologies (electric vehicles and hydrogen vehicles) typically have higher efficiency, so the final energy use in the sector reduces to 1.0–2.4EJ. The share of transportation sector in overall final energy, which was around 25% in 2010, decreases to around 15% in most models.
Figure 4 shows fuel share of final energy use by sectors in 2010 and 2050. Two trends observed in all sectors from 2010 to 2050 are the decrease in the share of liquids and the increase in electrification rates (with the exception of the residential sector’s electricity share in the AIM/Enduse). The electrification rates increase mainly due to decreasing consumption of other fuels in the industry and residential sectors. In the commercial and transport sectors, the increasing electrification rates is attributed also to the increasing consumption of electricity along with decreasing consumption of other fuels (see also Fig. 3).
In the industry sector, the electrification rate stays the lowest among sectors at around 20%, an increase of only a few percentage points from 2010. One exception is the AIM/Hub (the only participating GE model), in which rapid electrification takes place up to 73% in 2050.In the residential sector, the electrification rate is the highest among all fuels in all models (46–75%), showing the importance in electrifying the residential end-use technologies. On the other hand, the share of liquids (mostly oil products) decrease significantly suggesting a need to initiating a phase out of oil water heater and stoves. The commercial sector, which has the highest electrification rate across sectors in all models (62–95%), sees the use of liquids disappear in three models implying limited use of oil and gas appliances (mainly for cooking, hot water, and space heating) in a decarbonized society. The transport sector sees a great increase in the share of electricity. In 2010 the share is very low at around 2%, but it increases to 20–40% in models.
As a complement, the share of hydrogen, a clean energy carrier competing with electricity, is described by sector. In the industry sector, hydrogen is introduced in 2050 with a share of 9% and 7% in IEEJ and TIMES-Japan respectively, while the electrification rates reach 23% and 29%. Likewise, in the transport sector, both electricity and hydrogen are introduced in 2050. In AIM/Enduse, electricity is 20% while hydrogen is 7% and in IEEJ, electricity is 24%, hydrogen is 19%. In TIMES-Japan, the share of hydrogen is higher than electricity, with electricity at 40% while hydrogen at 44%.
Carbon intensity (the emission amount per unit final energy use) is reduced across all models in 2050. Looking at the CO2 emissions (Fig. 2) and the final energy use (Fig. 3) in each sector from 2010 to 2050, the demand sector’s carbon intensities in 2010 is 48–56 g-CO2/MJ, but they are reduced to 22–29 g-CO2/MJ in 2050 (Fig. 5). The lowest carbon intensity is seen in the commercial sector (0–22 g-CO2/MJ), followed by the residential sector (11–28 g-CO2/MJ). The model average of carbon intensity in the industry sector including industrial processes (28 g-CO2/MJ) and the transportation sector (30 g-CO2/MJ) remain to be high-emitting sectors.
The carbon intensity strongly depends on the ratio of fuel types in the final energy use. The value of carbon intensity increases as the share of fossil fuels increases, and the carbon intensity decreases as the share of clean energy carriers, such as electricity and hydrogen, increase. Therefore, sectors with high electrification rates have low-carbon intensities as shown in Fig. 5 and contribute greatly in reducing the demand-side emissions.
VREs and nuclear generation sensitivity
In order to analyze the effects of available VREs and nuclear generation, scenarios with high and low VRE costs, high and low VRE resource potential, and no nuclear (LoVREcost, HiVREcost, HiVREpot, LoVREpot, and NoNuc) are compared. Figure 6 shows the share of energy carriers in each scenario by models. Although electrification rates are different in each model, all models maintain electrification rates close to the level of 26by30 + 80by50_Def scenario as the change ranges between − 4.3 and + 6.5%pt (see also Figure ESM3).
A notable change in the share of final energy is seen in the following scenarios. AIM/Enduse shows a higher electrification rate (+ 1.2%pt) in the HiVREcost scenario than the 26by30 + 80by50_Def scenario because the electricity consumption is slightly higher (+ 0.01EJ) while the final energy use decreases by 0.24EJ. In AIM/Hub, the electrification rate decreases from the 26by30 + 80by50_Def scenario in the HiVREcost (− 4.3%pt) and the NoNuc (− 2.2%pt) scenarios by increasing liquids consumption, while the electrification rate increases from the 26by30 + 80by50_Def scenario in the LoVREcost (+ 4.5%pt) and the HiVREpot (2.1%pt) scenarios by decreasing liquids consumption. In DNE21, only the NoNuc scenario shows a slight decrease in the electrification rate (− 0.2%pt) from 26by30 + 80by50_Def because DNE21 has a high share of nuclear power generation due to no quantity constraint (see Shiraki et al. 2021) in 26by30 + 80by50_Def. IEEJ and TIMES-Japan models show a competitive nature between VRE and hydrogen. Hydrogen consumption decreases when more VREs electricity becomes accessible (LoVREcost and HiVREpot), while hydrogen consumption increases when electricity from VREs and nuclear becomes limited (HiVREcost, LoVREpot and NoNuc).
The electrification rate correlates positively with the availability of VREs and nuclear power sources, but the cases considered in this modeling exercise were not enough to change the electrification rates drastically. When availability of nuclear is restricted, VRE replaced the generation and vice versa. In summary, the cost and availability of VREs and nuclear generation does not change the need for electrifying the demand sector to achieve the 80% reduction in 2050.
Figure 7 shows the share of final energy carriers and CO2 emissions in the NoCCS scenario by models. Models maintain electrification rates close to the level of 26by30 + 80by50_Def scenario as the change ranges only between − 0.2 and + 1.8%pt. One exception is AIM/Enduse, which sees a notable increase of 8.8%pt as over 100Mt of CCS is deployed on the demand side (around 110Mt-CO2 in the industry sector including industrial processes) in 26by30 + 80by50_Def. When CCS is not available, AIM/Enduse decreases gas consumption and increases electricity demand to reduce CO2 emissions in the residential and commercial sectors to compensate for the increasing emissions in the industry sector.
Emissions policy sensitivity
Figure 8 shows the changes in the share of final energy carriers when the emission reduction target for 2050 is 70%, 80%, 90%, and 100% (26by30 + 70by50_Def, 26by30 + 80by50_Def, 26by30 + 90by50_Def, and 26by30 + 100by50_Def). Some models were not able to provide results as the emissions policy became extremely stringent. (26by30 + 90by50_Def: IEEJ, TIMES-Japan; 26by30 + 100by50_Def: AIM/Enduse, IEEJ and TIMES-Japan).
When a stricter emissions reduction policy is applied, the electrification rates increase in all models (Fig. 9), showing the importance of electricity as a clean energy carrier in the demand sector. Electricity typically replaces gases and liquids, but in some models (DNE21, IEEJ) the gases consumption increases with tighter emissions targets. An increase in hydrogen consumption with tighter emissions targets is also observed in AIM/Enduse, IEEJ and TIMES-Japan, all the models with a hydrogen option.
In AIM/Enduse, electricity consumption increases from 3.1 to 3.7EJ (860–1030TWh) as the emissions target gets tighter from 70 to 90%. The biggest reduction seen is in gases as the consumption decreases from 2.0 to 0.9EJ followed by liquids from 2.3 to 1.9EJ.
AIM/Hub’s electricity consumption increases from 6.5 to 7.8EJ (1800–2160TWh) as the emissions target gets tighter from 70 to 100%. The increase in the electricity consumption replaces gases and liquids as the gases decrease from 0.8 to 0.1EJ, and liquids decrease from 4.4 to 1.0EJ.
In DNE21, the electricity consumption stays the same from 70 to 90% reduction targets at 4.5EJ (1260TWh) but increases to 4.7EJ (1300TWh) in 100% reduction target. The consumption of liquid decreases from 6.6 to 2.3EJ as the emission target gets tighter from 70 to 100% as in all models, but the consumption of gases increases from 1.8 to2.7EJ.
In IEEJ, the electricity consumption increases from 2.9 to 3.0EJ (820–830TWh) as the emissions target gets tighter from 70 to 80%. The coal and liquids demand decrease as in other models, but the biggest increase is seen in hydrogen which increases from close to zero to 0.5EJ.
In TIMES-Japan, the electricity consumption increases from 3.9 to 4.1EJ (1090–1130Wh) as the emissions target gets tighter from 70 to 80%. Like IEEJ, the TIMES-Japan sees a decrease in liquids and gases while hydrogen increases the most from 0.3 to 1.2EJ.