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Article

Global Decarbonization: Current Status and What It Will Take to Achieve Net Zero by 2050

by
Hon Chung Lau
1,2,* and
Steve C. Tsai
1
1
Low Carbon Energies LLC., Bellaire, TX 77401, USA
2
Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005, USA
*
Author to whom correspondence should be addressed.
Energies 2023, 16(23), 7800; https://doi.org/10.3390/en16237800
Submission received: 3 November 2023 / Revised: 20 November 2023 / Accepted: 21 November 2023 / Published: 27 November 2023
(This article belongs to the Topic Carbon Capture, Storage and Utilisation Technologies (CCS/CCU)—2nd Volume)
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Abstract

:
A review of global CO2 emissions over the last century shows that emissions from 80 economies contributed to 95% of global emissions. Among them, 55 economies were decarbonizers, where CO2 emissions had either plateaued or were declining, while 25 economies were polluters, where CO2 emissions were still increasing. In 2021, the global CO2 emissions were 37.1 Gtpa, with 56% coming from polluters and 39% from decarbonizers. If current trends continue, global CO2 emissions will reach 49.6 Gtpa by 2050, with 81% coming from polluters and 14% from decarbonizers. Only 14 economies will reach net zero. The decarbonization target, over and above current efforts, to achieve net zero is calculated for each economy. Decarbonizers need to mitigate 230 Mtpa CO2 and polluters 1365 Mtpa CO2 beginning in 2021 to reach the net-zero target by 2050. This target will increase each year decarbonization is delayed. Analyses show that renewable energies’ share in the total final energy consumption in most economies increased by an average of only 4 percentage points in the last decade, which is inadequate for achieving net zero by 2050. Other means of decarbonization, including low-carbon fossil solutions through carbon capture and storage, will be needed. Pathways to accelerate decarbonization are proposed and their policy implications are discussed.

1. Introduction

Since the signing of the Paris Agreement in 2015, 196 countries have agreed to reduce their anthropogenic greenhouse gas (GHG) emissions in order to maintain the global rise of atmospheric temperature below 1.5 °C above pre-industrial times [1]. This is driven by the belief of many scientists that global warming is caused by anthropogenic GHG emissions [2,3,4]. Among GHGs, CO2 is the most important due to its vast quantity and greenhouse gas effect. Some scientists believe the effect of CO2 on global warming is irreversible [5,6].
In the last 120 years, global CO2 emissions from the combustion of fossil fuels have grown 19-fold from 1.95 Gtpa in 1900 to 37.1 Gtpa in 2022 [7]. To achieve the 1.5 °C target, many climate scientists believe that global GHG emissions should be reduced by 45% by 2030 and reach net zero by 2050 [8]. Hitherto, over 70 countries have pledged to achieve net zero by 2050 [9,10]. They include the biggest emitters, such as China [11], the USA [12], India [13] and the European Union [14], and cover 76% of global emissions. Today, more and more businesses are committed to achieving net zero by 2050, as this has become a license to operate in many countries [15,16,17,18,19,20].
Global decarbonization has received much attention in the academic literature in the last five years. In a recent review paper on energy transition, Lau et al. (2021) argued that decarbonization should be considered according to energy-consumption sectors, with power (electricity), transport and industry being the three major ones [21]. Furthermore, each country will choose an energy transition pathway depending on its particular energy and social context. A recent report by the McKinsey (2022) consulting firm predicted that future capital investment in physical assets for energy and land-use systems will reach USD 9.2 trillion per year in 2050 or USD 3.5 trillion per year more than in 2021, with most of the investment concentrated on the power, transport and industry sectors [22]. Jackson et al. (2018) argued that the current global energy growth is outpacing decarbonization [23]. They identified 19 countries whose GDP grew and whose CO2 emissions declined over the last decade. However, their efforts were outpaced by CO2 emissions from other countries. Rockstrom et al. (2017) proposed a simple carbon law, namely, halving anthropogenic CO2 emissions every decade, as a roadmap for achieving net zero by 2050 [24]. However, Urpelainen (2017) argued that this roadmap, though mathematically possible, is unrealistic because it is not based on the energy and social context of individual countries [25]. To be useful, decarbonization roadmaps need to be tailored to local conditions and address the barriers to policy implementation. Several country-specific decarbonization roadmaps for Singapore [26,27], Malaysia, Indonesia [28], Thailand [29,30], Vietnam [31], Taiwan [32] and Canada [33,34] were published recently with due consideration given to the unique energy landscape of each country.
Various agencies published their energy forecast scenarios to predict sectorial or global CO2 emissions under different future scenarios. For example, the US Renewable Energy National Laboratory (NREL) published its standard scenarios for the US power sector, which are updated annually based on US energy policies [35,36]. Several international oil companies, such as Shell, ConocoPhillips, Exxon and BP, published energy scenarios based on their respective outlook of the energy future [37,38,39,40]. The International Energy Agency (IEA) published scenarios capturing current government policies, what was pledged and what will be needed to achieve net-zero emissions by 2050 or soon afterward [41,42,43]. In this study, rather than advocating for any of the aforementioned energy scenarios, we assumed that the current energy trend of each country will continue till 2050 and determine what more is needed to meet the net-zero goal by 2050.
Hitherto, the debate on global decarbonization seems mostly centered on the increased use of renewable energies [8,44], and increasingly, more people are advocating for a total ban on fossil fuels [45,46,47,48]. However, this approach is rather one-sided and does not consider the limit to the pace at which renewable energy capacities can be added and the contributions from low-carbon fossil energies, such as fuel switching, and the use of carbon capture and storage (CCS) [21]. In this study, we examined historical CO2 emissions and the pace of global decarbonization over the last two to three decades to understand the current status. We then forecasted global CO2 emissions by 2050 and what decarbonization targets, over and above current efforts, will be needed to achieve net zero by 2050. Then, we discuss options to achieve these targets.

2. Objectives and Methodology

The objectives of this study were threefold. First, a look back at global CO2 emissions over the last 120 years was conducted to understand the historical trend and current status. Second, using recent historical trends, we forecasted CO2 emissions by 2050 and determined the extra decarbonization efforts, over and above current efforts, that will be needed to achieve net zero by 2050 for the top 80 CO2 emitters of the world. Third, we discuss pathways to accelerate decarbonization for various economies and their policy implications.
A linear history matching and forecasting method was used to analyze CO2 emissions data. The methodology is illustrated in Figure 1. From the global database of CO2 emissions from Our World in Data [7], we selected the top 80 CO2 emitters and classified them into two groups. The first group was called decarbonizers and consisted of economies where CO2 emissions had either peaked or were in decline. The second group was called polluters and consisted of economies where CO2 emissions were still increasing. In this study, economies were either countries or territories that reported accurate data on CO2 emissions. After determining the historical CO2 increase rate from the historical data, we extended the historical CO2 emissions trends linearly into the future to determine the CO2 emissions by 2050. We also calculated the CO2 decline rate needed to achieve net zero by 2050 using the CO2 emissions rate in 2021. The difference between this rate and the historical rate gave the target decarbonization rate in 2021, over and above current efforts, to achieve net-zero emissions by 2050. Assuming decarbonization was delayed beyond 2021, the decarbonization target was recalculated based on the CO2 emissions forecast. Thus, we determined the decarbonization targets for every polluter and decarbonizer between 2021 and 2050. We then grouped economies into coal-dominated, gas-and-oil-dominated, and non-fossil-energy-dominated economies and discussed their respective decarbonization pathways and policy implications.

Comparison of Study Methodology with IEA Scenarios

It is worthwhile to compare our forecast methodology with the four global energy forecast scenarios proposed by the IEA (Figure 2). The business-as-usual (BAU) scenario assumes that few or no steps are taken to limit greenhouse gas emissions. Therefore, unabated CO2 emissions will continue to increase with the increased use of fossil energies due to the growth in population and prosperity. The second is the stated policies scenario (STEPS), which reflects the current policy settings of each country as of August 2023 [42]. The announced pledges scenario (APS) assumes that all climate commitments made by governments and industries as of August 2023 will be met [41]. The sustainable development scenario (SDS) assumes that significant actions will be taken to limit the global temperature increase to 1.5 °C and thereby reduce global CO2 emissions to about 10 Gtpa by 2050 [43]. The net-zero (NZE) scenario assumes that net zero will be achieved by 2050 [49]. Although the IEA scenarios are global scenarios, they may be adapted to individual countries or economies.
Figure 3 and Figure 4 show how our forecast method fits in the context of IEA’s four scenarios for a decarbonizer and polluter, respectively. Our forecast did not assume any of the four IEA scenarios for any economy. It just extrapolated the current trend into the future. For a decarbonizer, the current trend may lie between STEPS and APS (Figure 3), which still falls short of the NZE scenario. Our forecasting method showed what it will take to accelerate the current trend to meet net zero by 2050 by assuming different years for the start of this acceleration. Each year a decarbonizer delays in starting the extra effort will make it more difficult to achieve the net-zero goal by 2050. For a polluter, the current trend may fall between BAU and STEPS (Figure 4). Our forecasting method calculated the extra effort needed to achieve the NZE scenario by beginning the extra effort at different years. The extra effort to achieve net zero by 2050 will be much greater for a polluter than a decarbonizer. The validity of our forecast was based on the length of time used to establish the current trend, which was at least one decade and may be as long as three decades. See figures in Section 5 for the USA and China, respectively.

3. Look Back and Classification

Figure 5 shows the annual CO2 emissions history for decarbonizers over the last 120 years [7]. There were 55 economies where CO2 emissions had either peaked or were declining. The complete list is given in Table 1. Among the decarbonizers, the biggest CO2 emitters were the USA, Japan, Germany, South Korea, Canada, Brazil, South Africa, Mexico, Australia and the United Kingdom (UK).
Figure 6 shows the CO2 emissions history for polluters over the last 120 years [7]. There were 25 economies where CO2 emissions were still increasing. The complete list is given in Table 2. Among the polluters, the biggest CO2 emitters were China, India, Russia, Iran, Saudi Arabia, Indonesia, Turkey, Vietnam, Malaysia and Egypt.
Figure 7 shows the aggregate CO2 emissions for polluters, decarbonizers and the rest of the world (others). It can be seen that between 2001 and 2021, CO2 emissions have dropped by 1.520 Gtpa for decarbonizers but have increased by 12.49 Gtpa for polluters. The net change between the two was 10.97 Gtpa. Global CO2 emissions were still increasing at 407 Mtpa in 2021, as calculated from the slopes of the curves for polluters, decarbonizers and “others” in Figure 7

4. Global CO2 Emissions Forecast

For each economy, we used a straight line to best fit the CO2 emissions data for the last two to three decades. We extended this line into the future to determine the CO2 emission by 2050 and the net-zero time for decarbonizers. The results are given in Table 1 for decarbonizers and Table 2 for polluters. When the results for all 55 decarbonizers were summed, we obtained the CO2 emissions forecast for decarbonizers, as shown in Figure 8. The same was done for the 25 polluters, with the results given in Figure 9. It is worthwhile to emphasize that a linear trend appeared to be the best fit for historical CO2 emissions data for most countries. A nonlinear history match was usually not a good match and gave an unreliable forecast.
Using this methodology, we estimated that the CO2 emissions for decarbonizers, as a group of economies, were changing at a rate of −261 Mtpa. Thus, their CO2 emissions will reach 6.74 Gtpa by 2050 and net zero will be reached by 2076 (Figure 8). Similarly, our calculations show that the CO2 emissions for polluters will increase at a rate of +644 Mtpa and will reach 39.6 Gtpa by 2050 (Figure 9). Using this method, we estimated that the CO2 emission for other economies was increasing at a rate of 23.7 Mtpa and will reach 2.6 Gtpa by 2050 (Figure 10). As of 2021, the global CO2 emissions were 37.1 Gtpa, with 56% coming from polluters, 39% from decarbonizers and 5% from other economies (Figure 11a). If current CO2 emission rates continue, our study forecasted that the global CO2 emissions will increase to 49.3 Gtpa in 2050 (Figure 11b), with 80% coming from polluters, 14% from decarbonizers and 5% from other economies. Consequently, the current emission rates of CO2 will not allow the world to achieve peak CO2 emissions by 2050, let alone reach net zero, as evidenced by Figure 7. In short, the increasing CO2 emissions by polluters will more than offset the CO2 abatement by decarbonizers, and the world as a whole is losing ground on decarbonization.
Our calculations showed that if current CO2 emission rates continue, only 14 economies will achieve net zero by 2050. They were the UK, Italy, Spain, Ukraine, Greece, Portugal, Finland, Serbia, Denmark, Estonia, Trinidad and Tobago, Venezuela, South Korea and Japan. Together they contributed only 8.4% of the global CO2 emissions in 2021. Therefore, a drastic change in the way economies tackle decarbonization will be needed over and beyond what they are doing, if they are to achieve net zero by 2050.

5. Decarbonization Target to Achieve Net Zero by 2050

To quantify what efforts, over and above current ones, will be needed to meet the net-zero target by 2050, for each of the 80 economies, we estimated the decarbonization target rate to achieve this. The method to calculate this is illustrated for a decarbonizer (USA) in Figure 12 and a polluter (China) in Figure 13. In these figures, we drew a straight line connecting the emissions in 2021 to the x-axis at 2050. This is the decarbonization rate needed to achieve net zero by 2050 assuming the 2021 CO2 rate was neither increasing nor decreasing. This rate was −172.7 Mtpa for USA (Figure 12) and −395.6 Mtpa for China (Figure 13). The target decarbonization rate in 2021 to achieve net zero by 2050 was the difference between this rate and the current decarbonizing rate in 2021. This target rate was −101.3 Mtpa for the USA (Figure 12) and −771.4 Mtpa for China (Figure 13). To obtain the target decarbonization rate for subsequent years, we drew a straight line from the CO2 emissions forecast for subsequent years to the x-axis at 2050 and repeated the same calculations.
Figure 14 shows the target decarbonization rates for decarbonizers and polluters as groups of economies. For decarbonizers, the target decarbonization rate started at 230 Mtpa in 2021 and increased to 500 Mtpa by 2030. As time approaches 2050, this target rate will increase rapidly. For polluters, the target decarbonization rate started at 1365 Mtpa in 2021 and will increase to 2000 Mtpa for the year 2030 and 4400 Mtpa for the year 2040. Thereafter, it will increase sharply as 2050 was approached. The target decarbonization rates for economies with the biggest targets are shown in Figure 15. Figure 14 and Figure 15 show clearly that there was a big difference in target decarbonization rates to achieve net zero by 2050 between polluters and decarbonizers. Polluters required a much bigger target decarbonization than decarbonizers. For both, the target decarbonization rate will increase with time. As 2050 approaches, the target decarbonization rate will be too high to be achievable. This means that decarbonization must begin as soon as possible. Each year of delay in beginning decarbonization will make subsequent decarbonization more difficult and expensive.

6. Decarbonization Pathways

The target decarbonization rates in 2021 to achieve net zero by 2050 are shown in the second-to-last column in Table 1 and Table 2. Figure 16 compares the target decarbonization rates in 2021 for 20 economies with the highest targets. The economies with the highest decarbonization targets are China, India, the USA, Russia, Saudi Arabia, Iran and Indonesia. Their efforts will be critical for global decarbonization. It is worthwhile to note that there are some big CO2 emitters, e.g., Japan, South Korea, the UK and Italy, that do not appear on this list because they have low decarbonization targets since their current decarbonization rates are relatively high.
To determine the pathways for decarbonization, we divided economies into three categories: coal-dominated (Table 3), gas-and-oil-dominated (Table 4), and non-fossil-dominated (Table 5) and discuss decarbonization pathways for each. Out of the 80 economies included in the aforementioned analysis, only 66 reported data on their composition of total final energy consumption (TFEC) in 2021 [50]. Hence, in the following sections, we focus on these 66 economies.

6.1. Decarbonization Technologies

Decarbonization technologies can be divided into demand-side and supply-side technologies. On the energy demand side, increasing energy efficiency [51] and reducing demand [52] are key areas but are outside the scope of this paper. Decarbonization technologies on the energy supply side can be classified into four types (Table 6). The first type is renewable energies (REs), including wind, solar, bioenergy, geothermal and hydroelectricity [53]. They are mostly applied to the power (electricity) sector but can be applied to the transport sector through the use of electric vehicles, which have been gaining acceptance in recent years. In fact, renewable energies have been applied in many economies and contributed to 27.9% of global electricity and 13.5% of global total final energy consumption (TFEC) in 2021 [50]. Hitherto, most of the efforts on decarbonization have been focused on RE.
The second type of decarbonization technology is low-carbon fossil energies. They include (1) switching from coal to gas for power and heat generation (coal → gas), applying CCS to coal-fired power plants (CP-CCS), gas-fired power plants (GP-CCS) and industrial plants (Ind-CCS) [28,54,55]. Coal → gas is a mature technology and has the potential to halve CO2 emissions in power generation, as the combustion of gas produces approximately half the CO2 compared with coal [56]. It has been implemented in many advanced and growing economies. CCS has been applied commercially in Norway [57,58] and is currently being implemented in tens of projects worldwide [59], especially in countries that have a carbon tax or credit. It has been gaining momentum in the USA, where economic incentives have been increased through the 45Q tax regulations [60]. Another type of low-carbon fossil decarbonization technology is carbon capture and utilization, which seeks to turn anthropogenic CO2 into useful commercial products [61]. However, these technologies are still in the R&D stage and not ready for commercialization [61].
The third type of decarbonization technology is hydrogen. Though hydrogen is not an energy source, it is an energy carrier like electricity. It can be used to generate electricity through a hydrogen fuel cell or combusted to produce heat. Consequently, hydrogen can be used for the transport sector through the use of hydrogen fuel cell vehicles or used to replace fossil fuels for industrial heating and power generation. Green hydrogen is produced via the electrolysis of fresh water with renewable electricity. It is called “green” because this process does not produce CO2 [62]. However, this is the most expensive form of hydrogen and currently costs USD 3–7/kg [63]. Blue hydrogen is produced from natural gas through steam methane reforming or coal through coal gasification with emitted CO2 mitigated by CCS. Both processes are technologically mature [21]. Currently, blue hydrogen is roughly half (USD 1.5–2.3/kg) as expensive as green hydrogen [63]. Besides being used to fuel hydrogen fuel cell vehicles, hydrogen can be used to replace coal or gas in industries requiring high temperatures (over 1000 °C), such as steelmaking, cement manufacturing, natural gas processing and raw material in the petrochemical processes. Hydrogen is therefore useful to decarbonize the “hard-to-decarbonize” industrial sector. At present, neither green nor blue hydrogen is manufactured at a commercial scale.
The fourth type of decarbonization technology is nuclear energy. The use of conventional nuclear energy is a country-specific issue. Some countries, e.g., France and Ukraine, favor the use of nuclear energy, whereas many others, e.g., Southeast Asian countries, do not. Conventional nuclear energy suffers from a long lead time from proposal to government approval, which could take up to a decade. In addition, the disposal of nuclear waste is also an issue. Recently, there has been interest in the use of advanced small modular reactors (SMRs) of capacity up to 300 MWe, which are faster to build and deploy and can be used for industrial applications or remote areas with limited grid capacity. However, SMRs are still in the research and development stage [64].
Table 6. Supply-side decarbonization technologies.
Table 6. Supply-side decarbonization technologies.
Renewable EnergiesLow-Carbon Fossil EnergiesNuclear EnergyHydrogen
Main types
  • Wind
  • Solar
  • Bioenergy
  • Geothermal
  • Hydroelectricity
  • Coal → gas
  • CP-CCS
  • GP-CCS
  • Ind-CCS
  • Conventional
  • Advanced small modular reactor (SMR) [64]
  • Green H2
  • Blue H2 (coal → H2-CCS; gas → H2-CCS)
Main use
  • Power sector
  • Transport sector through EV
  • Power sector
  • Industry sector
  • Power sector
  • Transport sector
  • Industry sector
  • Power sector
Comments
  • Applied in many economies
  • Technologically mature; commercial applications increasing
  • Application is country-specific
  • SMRs in R&D stage
  • Green H2 requires renewable electricity and fresh water
  • Blue H2 comes from gas or coal with CCS

6.2. Slow Pace of Addition of Renewable Energy Capacity

In the last column of Table 3, Table 4 and Table 5, we have listed the change in RE’s share of TFEC over the last decade (2011 to 2021) [50]. For coal-dominated economies, Australia’s gain in RE’s share of TFEC was 9.36 percentage points (pp) over a decade and was the largest (Table 3). This was still less than 1 pp per year. The average increase was only 4.31 pp over a decade. For oil-and-gas-dominated economies, European economies had the biggest gain in RE in the last decade (Table 4). The biggest gain was achieved by the UK (13.98 pp), Germany (13.77 pp), Greece (13.77 pp), Austria (10.39 pp) and the Netherlands (9.68 pp). Ecuador was the only economy in South America with a sizeable gain in RE (15.47 pp). Both the USA and Canada achieved small gains of 5.39 pp and 2.78 pp, respectively. The average increase in RE’s share of TFEC was 4.58% over a decade (Table 4). All non-fossil-dominated economies exhibited sizable gains in the RE share of TPEC in the last decade, ranging from 7 pp to 15 pp (Table 5). The average increase in RE’s share of TFEC was 10.42 pp over a decade (Table 5). These numbers show that the pace of the addition of RE’s share of TFEC was relatively slow and was about 0.4 pp per year for most economies. Even if this rate were tripled, the goal of a near 100% in RE’s share of TFEC by 2050 cannot be achieved. There are two reasons for this slow growth in RE’s share of TFEC. First, renewable energies’ (RE) share of TFEC will only increase if the growth in RE is larger than the growth in fossil fuels. However, in many economies, the growth in the fossil fuel capacity surpasses that of the RE capacity. Therefore, unless more RE capacity is installed, the overall growth in the RE share of TPEC is negative. Second, wind and solar have a lower capacity utilization rate (<20%) than fossil fuel (>40%) in power generation [55]. Therefore, replacing fossil power generation capacity with wind and solar requires a much higher wind or solar capacity.

6.3. Decarbonization for Coal-Dominated Economies

These are economies where coal’s share of TFEC was 25% or higher in 2021 [65]. There were 15 economies in this group. They included China, India, Australia, Indonesia and Japan, which are some of the biggest CO2 emitters in the world. The compositions of TFEC by fuel type in these economies are listed in Table 3. In these economies, the majority of CO2 is emitted by the combustion of coal. Consequently, the decarbonization effort should be directed at reducing CO2 emissions from the combustion of coal.
In general, there are two demonstrated ways to decarbonize coal-dominated economies. The primary way is to replace the use of coal for power and heat generation with gas. This has the potential to reduce CO2 emissions by one-half [56]. To achieve this, coal-fired power plants have to be repurposed for using gas as fuel. An alternative decarbonization method is to install CCS in coal-fired power plants to mitigate the emitted CO2. This will require compressing the captured CO2 and transporting it to nearby oil or gas reservoirs, or using saline aquifers for permanent storage. A recent study by Lau showed a potentially large contribution of retrofitting CCS in existing coal-fired power plants in several Asian countries [66]. Which method is preferred will depend on the availability of gas to replace coal and the availability of suitable subsurface storage sites for CO2 storage. The secondary decarbonization method is to install CCS in gas-fired power plants to further reduce CO2 emissions.

6.4. Decarbonization of Gas-and-Oil-Dominated Economies

These are economies where the share of oil and gas in TFEC was 50% or higher in 2021. There were 45 economies in this group. The aggregate CO2 emissions from them were only 58% of that of coal-dominated economies (Table 3 and Table 4). The compositions of TFEC in 2021 for these economies are given in Table 4. In these economies, gas was used mostly for power and heat generation, whereas oil was mostly used as fuel for transport. The main decarbonization pathway was to use CCS in natural gas-fired power plants (GP-CCS) and, secondarily, CCS in industry plants (Ind-CCS) and coal-fired power plants (CP-CCS). For road transport, the main decarbonization pathway was to use electric vehicles (EVs) to replace internal combustion engine vehicles. This will shift mobile CO2 emissions from vehicles to stationary emissions at power plants. The latter may be mitigated by CCS if fossil fuels are used for power generation.
The biggest CO2 emitters from this group are the USA, Russia, the UK, Iran, Saudi Arabia, Germany and South Korea (Table 4). Except for Belgium and South Korea, nuclear energy’s share of TFEC in 2021 in this group of economies was less than 10%.

6.5. Decarbonization of Non-Fossil-Energy-Dominated Economics

These economies were dominated mostly by renewable and nuclear energies and their aggregate share of TFEC was larger than 45%. There were six economies in this category and their compositions of TFEC in 2021 are given in Table 5. Among them, France was the one with the most nuclear energy (36.4%). Other economies were mostly dominated by renewable energies. Among them, Brazil and France were the biggest CO2 emitters in 2021. Decarbonization of these economies will require the further expansion of nuclear power, possibly by using SMR [64] and renewable electricity, to replace gas for power generation. The secondary decarbonization pathway is the further electrification of road transport to replace gasoline with electricity as a transportation fuel.

7. Discussion

The decarbonization pathways for an economy will vary according to the composition of its TFEC. The suggested pathways are summarized in Table 7. It should be emphasized that these pathways are over and above current efforts to increase energy efficiency and install renewable energy capacities. Many of these pathways can be classified as low-carbon fossil pathways that include switching from coal to gas for power and heat generation (coal → gas) and mitigating CO2 emission from the combustion of fossil fuels using CCS (CP-CCS, GP-CCS, Ind-CCS). Given the urgency for decarbonization, there is a need to use all available tools in our toolkit to accelerate decarbonization. Low-carbon fossil solutions should be considered, together with RE and nuclear energy. The optimal path for each economy will likely depend on the availability of fossil, renewable, and nuclear energy resources and CCS options. It should also be noted that the decarbonization pathways in Table 7 are only suggestions and could be incomplete. Other decarbonization options can be included depending on their technology and commercial readiness level.

8. Policy Implications

If current CO2 emission rates continue, our analysis shows that only 14 economies will achieve net zero by 2050. There is, therefore, an urgent need for most economies to accelerate the pace of decarbonization over and above the current pace of the addition of RE capacity. Consequently, low-carbon fossil solutions, including switching from coal to gas for power and heat generation (coal → gas) and installing CCS in coal- and gas-fired power plants (CP-CCS, GP-CCS) and industrial plants (Ind-CCS) will be needed. According to the Global CCS Institute, as of September 2022, there were 30 CCS projects operating in the world mitigating 43 Mtpa; another 164 projects are in various phases of development and will add 201 Mtpa of CCS capacity [59]. Moreover, CCS has been gaining momentum over the last few years. The already sanctioned Longship project in Norway will be in operation by 2024 and will sequester 0.8 to 5.0 Mtpa CO2 [67,68]. It may become the first cross-border CCS project in the world. The Porthos [69,70] and Aramis [71] CCS projects in the Netherlands will sequester 2.5 Mtpa and 5.0 Mtpa CO2, respectively. The East Coast Cluster CCS project in the UK will sequester 26 Mtpa CO2, almost 50% of CO2 emissions from the UK’s industrial sector [72,73]. Talos Oil has started operations in the first offshore CCS project in the Gulf of Mexico near Port Arthur, Texas, in cooperation with several other companies [74,75,76]. The Houston CCS Alliance plans to sequester 100 Mtpa CO2 by 2040 [77]. These projects are all located in countries that have imposed a substantial carbon tax or credit. In 2022, the carbon taxes in Norway, the Netherlands and the UK were USD 88, USD 46 and USD 24, respectively [78]. In 2022, the US government increased the carbon credit from USD 45 to USD 85 per tonne CO2 [79]. Outside of Europe and North America, most countries do not have a carbon tax or credit. However, Aramco has announced it will establish a CCUS hub in Jubail [80,81,82,83]. Malaysia already has several CCS projects under development [84,85,86] and Indonesia has expressed interest in CCS projects and passing related regulations [87,88]. China is also aggressively installing CCS projects, both onshore and offshore [11,89,90]. Imposing a credible carbon tax or credit will be the most important energy policy to incentivize companies to reduce their CO2 emissions. Next, the passing of CCS regulations on CO2 injection and monitoring will be needed. Furthermore, the transfer of long-term liability from the operator to the government will be needed to de-risk CCS projects and to obtain financing [21,72,73]. More public engagement on the benefits of CCS will also be needed to raise the level of public acceptance of CCS. Government funding of CCS R&D should include subsurface characterization of saline aquifers for CO2 storage [28].
In the transport sector, there appears to be a consensus among economies to replace the use of internal combustion engine vehicles with electric vehicles (EVs) [91,92]. This will drastically reduce CO2 emissions if the electricity used for EVs is generated using renewable energy or low-carbon fossil fuels. If the latter, CCS will be needed. To encourage the wider use of EVs, policies need to be enacted to incentivize the building of charging facilities [91,93], upgrading of the electric grid [94] and R&D of battery technologies [95].
In the longer-term future, the use of hydrogen to replace the use of fossil fuels to decarbonize the “hard-to-decarbonize” industrial sector will be needed [63]. Therefore, national governments will need to propose a hydrogen strategy or roadmap to underpin the increased use of hydrogen [96,97,98]. Since green hydrogen currently costs twice as much as blue hydrogen, it will probably not be available in large quantities for some time [63]. The use of blue hydrogen should therefore be considered [99].

9. Conclusions

The following may be concluded from this study:
  • The top 80 CO2 emitters contributed 95% of the global emissions in 2021. Among them, 55 were decarbonizers, where emissions had either peaked or were in decline; 25 were polluters, where emissions were increasing.
  • A linear history matching and forecasting method was applied to historical CO2 emissions data. The results show that global CO2 emissions will increase from 37.1 Gtpa in 2021 to 49.3 Gtpa in 2050 with polluters contributing to 81% and decarbonizers 14% of global CO2 emissions. Furthermore, only 14 economies will achieve net zero by 2050. They are the UK, Italy, Spain, Ukraine, Greece, Portugal, Finland, Serbia, Denmark, Estonia, Trinidad and Tobago, Venezuela, South Korea and Japan.
  • The target decarbonization rates to achieve net zero by 2050, over and above current efforts, were estimated for the 80 economies. These rates will increase rapidly as 2050 is approached. Therefore, decarbonization must start as soon as possible and any delay will only make future efforts more costly and difficult.
  • China, India, the USA, Russia, Saudi Arabia, Iran, Indonesia, Turkey, Vietnam and Canada have the largest decarbonization targets. Their efforts will determine the future of global decarbonization.
  • The average increase in RE’s share in TFEC was 0.4 pp per year for most economies over the last decade. Even if this rate were tripled, it is still inadequate to allow RE’s share in TFEC to approach 100% by 2050. Therefore, other decarbonization methods are urgently needed. They will vary with each country’s energy mix. Pathways for coal-dominated, gas-and-oil-dominated, and non-fossil-energy-dominated economies are suggested and their policy implications are discussed.

Author Contributions

Investigation, S.C.T.; Investigation and writing original draft, H.C.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Hon Chung Lau and Steve C. Tsai were employed by Low Carbon Energies LLC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Nomenclature

APSIEA’s announced pledges scenario
BAUBusiness-as-usual scenario
CCSCarbon capture and storage
Coal → gasSwitching from coal to gas in power generation
CP-CCSUse of CCS in coal-fired power plants
Coal → H2-CCSProduction of blue hydrogen through coal gasification and CCS
Gas → H2-CCSProduction of blue hydrogen through steam methane reforming and CCS
GP-CCSUse of CCS in gas-fired power plants
GHGGreenhouse gas
IEAInternational Energy Agency
Ind-CCSUse of CCS in industrial plants
NANot available
NRELNational Renewable Energy Laboratory
NZEIEA’s net-zero scenario
ppPercentage point
RERenewable energy
R&DResearch and development
SDSIEA’s sustainable development scenario
SMRAdvanced small modular nuclear reactor
STEPIEA’s stated policies scenario
TFECTotal final energy consumption
UKUnited Kingdom
Gtpa109 tonnes per annum
Mtpa106 tonnes per annum

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Figure 1. Methodology of study.
Figure 1. Methodology of study.
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Figure 2. Forecast scenarios by International Energy Agency (IEA).
Figure 2. Forecast scenarios by International Energy Agency (IEA).
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Figure 3. Comparison of current trend study methodology with IEA scenarios for a decarbonizer.
Figure 3. Comparison of current trend study methodology with IEA scenarios for a decarbonizer.
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Figure 4. Comparison of current trend study methodology with IEA scenarios for a polluter.
Figure 4. Comparison of current trend study methodology with IEA scenarios for a polluter.
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Figure 5. Annual CO2 emission from decarbonizers [7].
Figure 5. Annual CO2 emission from decarbonizers [7].
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Figure 6. Annual CO2 from polluters [7].
Figure 6. Annual CO2 from polluters [7].
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Figure 7. Global CO2 emissions.
Figure 7. Global CO2 emissions.
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Figure 8. CO2 emissions forecast for decarbonizers.
Figure 8. CO2 emissions forecast for decarbonizers.
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Figure 9. CO2 emissions forecast for polluters.
Figure 9. CO2 emissions forecast for polluters.
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Figure 10. CO2 emissions forecast for “other” economies.
Figure 10. CO2 emissions forecast for “other” economies.
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Figure 11. Global CO2 emissions in (a) 2021 and (b) 2050 (forecast).
Figure 11. Global CO2 emissions in (a) 2021 and (b) 2050 (forecast).
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Figure 12. Graphical method to determine decarbonization targets between 2021 and 2050 for USA.
Figure 12. Graphical method to determine decarbonization targets between 2021 and 2050 for USA.
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Energies 16 07800 g013
Figure 13. Graphical method to determine decarbonizer targets between 2021 and 2050 for China.
Figure 13. Graphical method to determine decarbonizer targets between 2021 and 2050 for China.
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Energies 16 07800 g014
Figure 14. Target decarbonization targets for polluters and decarbonizers.
Figure 14. Target decarbonization targets for polluters and decarbonizers.
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Figure 15. Target decarbonization targets for various countries.
Figure 15. Target decarbonization targets for various countries.
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Figure 16. Target decarbonization rate in 2021 to achieve net zero by 2050.
Figure 16. Target decarbonization rate in 2021 to achieve net zero by 2050.
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Table 1. CO2 emissions forecast and decarbonization targets for decarbonizers.
Table 1. CO2 emissions forecast and decarbonization targets for decarbonizers.
EconomyCO2 Emissions in 2021 (Mtpa) [7]Estimated Net-Zero DateEst. CO2 Emissions in 2050 (Mtpa)Current CO2 Increase Rate (Mtpa)CO2 Increase Rate to Reach Net Zero by 2050 (Mtpa)Decarbonization Target in 2021 to Achieve Net Zero by 2050 (Mtpa)Confidence Level of Forecast *
1USA500720912900−71.40−172.67−101.27M
2Japan1067205060−33.80−36.81−3.01M
3Germany6742108510−8.50−23.27−14.77H
4South Korea61620500−19.41−19.410.00L
5Brazil4892074215−8.90−16.86−7.96M
6Mexico4072064132−9.60−14.04−4.44M
7UK34720450−14.10−11.962.14H
8Italy32920470−11.90−11.330.57H
9Poland3292083147−4.51−11.33−6.82L
10France306206080−7.60−10.55−2.95H
11Thailand2782100177−3.50−9.60−6.10L
12Spain23420420−10.00−8.061.94M
13UAE2022098126−2.60−7.04−4.44L
14Ukraine20420420−9.70−6.962.74L
15The Netherlands141209791−1.90−4.86−2.96L
16Czechia97.1206125−2.40−3.35−0.95M
17Belgium95.7206936−1.90−3.30−1.40M
18Columbia91.7210058−1.14−3.16−2.02L
19Venezuela79.520270−14.10−2.7511.35M
20Romania79.3205511−2.04−2.74−0.71M
21Austria64.6211445−0.70−2.23−1.53L
22Belarus59.6NA600.00−2.06−2.06L
23North Korea56.4NA560.00−1.94−1.94L
24Greece56.320350−4.10−1.942.16H
25Israel54.520558−1.60−1.88−0.28L
26Hungary48.4208826−0.67−1.67−1.00L
27Bulgaria42.6206815−0.85−1.47−0.62M
28Ecuador41.3NA410.00−1.42−1.42L
29Norway40.9207720−0.73−1.41−0.69L
30Portugal40.820470−1.56−1.41−0.15M
31Finland37.620400−2.10−1.300.80H
32Ireland37.5207617−0.66−1.29−0.63L
33Trinidad & Tobago36.120470−1.40−1.250.15M
34Sweden35.8206312−0.95−1.24−0.29M
35Slovakia35.3207013−0.65−1.22−0.57M
36Switzerland34.920608−0.88−1.20−0.32M
37Serbia30.920500−1.33−1.060.26L
38Denmark29.620360−1.90−1.020.88H
39Syria27.0NA270.00−0.93−0.93L
40Sri Lanka20.8208612−0.33−0.72−0.39L
41Croatia17.720573.2−0.48−0.61−0.13M
42Lithuania13.9NA13.90.00−0.48−0.48L
43Slovenia12.520572.6−0.36−0.43−0.07L
44Estonia10.420350−0.82−0.360.46L
45Luxembourg8.420581.9−0.23−0.29−0.06M
46Canada545NANA0.00−18.81−18.81L
47South Africa436NANA0.00−15.03−15.03L
48Australia391NANA0.00−13.49−13.49L
49Taiwan283NANA0.00−9.75−9.75L
50Kazakhstan277NANA0.00−9.54−9.54L
51Argentina186NANA0.00−6.43−6.43L
52Uzbekistan122NANA0.00−4.19−4.19L
53New Zealand33.8NANA0.00−1.17−1.17L
54Singapore32.5NANA0.00−1.12−1.12L
55Hong Kong31.7NANA0.00−1.09−1.09L
Total14,310 −261−492−230
* L—low, M—moderate, H—high, NA—not available
Table 2. CO2 emissions forecast and decarbonization targets for polluters.
Table 2. CO2 emissions forecast and decarbonization targets for polluters.
EconomyCO2 Emissions in 2021 (Mtpa) [7]Est. CO2 Emissions in 2050 (Mtpa)Current CO2 Increase Rate (Mtpa)CO2 Increase Rate to Reach Net Zero by 2050 (Mtpa)Decarbonization Target in 2021 to Achieve Net Zero by 2050 (Mtpa)Confidence Level of Forecast *
1China11,47222,400375.80−395.60−771.40M
2India27105900106.70−93.44−200.14H
3Russia1756210012.00−60.54−72.54M
4Iran749125017.30−25.82−43.12H
5Saudi Arabia672136021.60−23.19−44.79H
6Indonesia619121019.00−21.35−40.35H
7Turkey44676010.71−15.39−26.10H
8Vietnam32684017.78−11.24−29.02M
9Malaysia2564907.25−8.83−16.08M
10Egypt2504807.04−8.61−15.65M
11Pakistan2293705.00−7.91−12.91M
12Iraq18652210.00−6.40−16.40L
13Algeria1763284.96−6.08−11.04M
14Philippines1442955.28−4.97−10.25M
15Nigeria1372523.98−4.71−8.70L
16Kuwait1061561.90−3.66−5.56M
17Qatar952003.30−3.30−6.60M
18Bangladesh931903.33−3.21−6.54H
19Chile851540.20−2.95−3.15H
20Turkmenistan831682.83−2.86−5.69M
21Oman811672.93−2.79−5.72H
22Libya751081.18−2.57−3.75L
23Morocco711181.70−2.43−4.13H
24Peru56941.28−1.94−3.22L
25Azerbaijan38530.47−1.33−1.80L
Total20,91339,965644−721−1365
* L—low, M—moderate, H—high, NA—not available
Table 3. Composition of TFEC in coal-dominated economies in 2021 [50].
Table 3. Composition of TFEC in coal-dominated economies in 2021 [50].
NumberCountryCoal’s Share of TFEC (Fraction)Oil’s Share of TFEC (Fraction)Gas’s Share of TFEC (Fraction)RE’s Share of TFEC (Fraction)Nuclear’s Share of TFEC (Fraction)CO2 Emissions (Mtpa)ΔRE Share of TFEC (2011–2021) (pp)
1South Africa0.7100.2090.0280.0340.0184363.02
2India0.5670.2660.0630.0930.01127102.34
3China0.5470.1940.0860.1500.02311,4708.26
4Kazakhstan0.5440.2200.1950.0420.0002771.19
5Vietnam0.4970.2170.0600.2260.0003268.03
6Poland0.4230.3110.1890.0770.0003294.93
7Philippines0.4010.4160.0610.1220.000144−3.70
8Indonesia0.3950.3410.1600.1040.0006196.58
9Taiwan0.3360.3860.1970.0300.0502831.11
10Czechia0.3210.2440.1960.0710.167973.28
11Morocco0.3200.5670.0310.0820.00071NA
12Australia0.2840.3370.2480.1310.0003919.36
13Ukraine0.2840.1380.2810.0630.2342024.39
14Japan0.2710.3730.2100.1160.03110675.98
15Turkey0.2550.2770.3020.1660.0004465.52
18,868 a4.31 b
a—total, b—average. NA = not available
Table 4. Composition of TFEC in oil-and-gas-dominated economies in 2021 [50].
Table 4. Composition of TFEC in oil-and-gas-dominated economies in 2021 [50].
NumberCountryCoal’s Share of TFEC (Fraction)Oil’s and Gas’s Share of TFEC (Fraction)RE’s Share of TFEC (Fraction)Nuclear’s Share of TFEC (Fraction)CO2 Emissions (Mtpa)ΔRE Share of TFEC (2011–2021) (pp)
1Turkmenistan0.0001.0000.0000.000830.00
2Qatar0.0001.0000.0000.000950.00
3Kuwait0.0001.0000.0000.000106NA
4Trinidad & Tobago0.0001.0000.0000.000360.00
5Saudi Arabia0.0000.9990.0010.0006720.09
6Oman0.0070.9930.0000.00081NA
7Singapore0.0090.9880.0030.000330.29
8Algeria0.0080.9880.0040.0001760.16
9Iraq0.0000.9860.0140.000186NA
10Azerbaijan0.0000.9850.0150.000380.90
11Iran0.0060.9790.0130.0027490.09
12UAE0.0150.9510.0110.0222021.10
13Uzbekistan0.0360.9390.0260.000122−1.86
14Egypt0.0130.9240.0630.000250NA
15Belarus0.0270.9190.0090.045600.90
16Bangladesh0.0850.9090.0060.00093−0.63
17Mexico0.0340.8440.1060.0164074.89
18Argentina0.0200.8400.1110.029186−0.40
19Hong Kong0.1720.8280.0000.000320.00
20The Netherlands0.0660.8010.1240.0091419.68
21Israel0.1520.7900.0570.000555.71
22Italy0.0360.7800.1840.0003297.88
23Thailand0.1590.7710.0700.0002783.84
24Russia0.1090.7600.0660.06417561.19
25UK0.0290.7340.1800.05734713.98
26Greece0.0670.7330.2000.0005613.77
27Hungary0.0590.7230.2180.000484.38
28Venezuela0.0000.7140.2860.000807.21
29Belgium0.0370.7020.0920.169965.87
30Malaysia0.2120.7020.0860.0002566.14
31USA0.1140.7000.1070.08050075.39
32Pakistan0.1740.6830.1060.036229NA
33Ecuador0.0000.6710.3290.0004115.47
34Peru0.0410.6690.2890.000414.65
35Portugal0.0110.6630.3260.000419.68
36Spain0.0290.6570.2240.0912348.93
37Romania0.1210.6210.1860.071798.26
38Sri Lanka0.1540.6150.2310.00021NA
39South Korea0.1790.6070.0370.1146163.05
40Canada0.0340.6070.2990.0605452.78
41Columbia0.0680.6020.3300.0005451.45
42Germany0.1680.5870.1950.04967413.77
43Chile0.1560.5750.2690.000858.50
44Austria0.0750.5510.3740.0006510.40
45New Zealand0.0830.5120.4050.000340.99
11,024 a4.58 b
a—total, b—average. NA = not available
Table 5. Non-fossil’s share of TFEC in non-fossil-dominated economies in 2021 [50].
Table 5. Non-fossil’s share of TFEC in non-fossil-dominated economies in 2021 [50].
NumberCountryCoal’s Share of TFEC (Fraction)Oil’s and Gas’s Share of TFEC (Fraction)RE’s Share of TFEC (Fraction)Nuclear’s Share of TFEC (Fraction)Non-Fossil’s Share of TFEC (Fraction)CO2 Emissions (Mtpa)ΔRE Share of TFEC (2011–2021) (pp)
1Norway0.0150.2600.7250.0000.725417.88
2Sweden0.0260.2580.5070.2100.7173612.83
3Finland0.1030.3620.3450.1900.5363814.99
4Switzerland0.0000.4670.3740.1590.533359.38
5France0.0240.4730.1380.3640.50230610.45
6Brazil0.0560.4710.4620.0100.4724896.98
944 a10.42 b
a—total, b—average.
Table 7. Suggested decarbonization pathways for various classes of economies.
Table 7. Suggested decarbonization pathways for various classes of economies.
Coal-Dominated EconomiesOil-and-Gas-Dominated EconomiesNon-Fossil-Energy-Dominated Economies
Number of economies15456
CharacteristicsCoal’s share of TFEC > 25%Oil and gas share of TFEC > 50%Non-fossil-energy’s share of TFEC > 45%
Biggest CO2 emittersChina, India, Australia, Indonesia, JapanUSA, Russia, UK, Iran, Saudi Arabia, Germany, South KoreaBrazil, France
Primary decarbonization pathway
  • Coal → gas
  • CP-CCS
  • GP-CCS
  • EVs
  • Nuclear
  • Renewables
Secondary decarbonization pathway
  • GP-CCS
  • Ind-CCS
  • CP-CCS
  • Ind-CCS
  • EVs
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Lau, H.C.; Tsai, S.C. Global Decarbonization: Current Status and What It Will Take to Achieve Net Zero by 2050. Energies 2023, 16, 7800. https://doi.org/10.3390/en16237800

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Lau HC, Tsai SC. Global Decarbonization: Current Status and What It Will Take to Achieve Net Zero by 2050. Energies. 2023; 16(23):7800. https://doi.org/10.3390/en16237800

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Lau, Hon Chung, and Steve C. Tsai. 2023. "Global Decarbonization: Current Status and What It Will Take to Achieve Net Zero by 2050" Energies 16, no. 23: 7800. https://doi.org/10.3390/en16237800

APA Style

Lau, H. C., & Tsai, S. C. (2023). Global Decarbonization: Current Status and What It Will Take to Achieve Net Zero by 2050. Energies, 16(23), 7800. https://doi.org/10.3390/en16237800

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