Research on Climate Change Initiatives in Nigeria: Identifying Trends, Themes and Future Directions

Abstract

Nigeria is among the countries highly vulnerable to climate change impact. Thus, there has been growing emphasis on the pursuit of decarbonization and net-zero (net-zero transition) strategies. The aim of this work is to review major concepts in research publications associated with climate change mitigation in Nigeria. The literature search was conducted on the Scopus database using relevant keyword operators. Mixed methods were adopted to conduct bibliometric, text mining and content analysis. Bibliometric software (VOSviewer) was used. The research objectives were to identify how net-zero transition research has evolved in Nigeria; their important research themes and trends in Nigeria, and potential directions for future research on achieving them in Nigeria. The results show that the number of publications in the field has been increasing, with 87% of the articles included in the dataset published between 2016 and 2024. Through data clustering, eight clusters of articles were identified, namely (i) the renewable energy, economic growth and emission reduction nexus (ii) energy transition in the Nigerian power system, (iii) policy drivers (socio-technical and economic) for a cleaner energy system, (iv) energy transition governance, (v) hybrid renewable energy systems, (vi) low-carbon transition, (vii) energy efficiency and low-carbon growth and others. By checking through the keywords used by authors, it appears that the most popular keywords are carbon neutrality, hydrogen, biomass, circular economy, and electric vehicles. These keywords further highlight areas of research interests. Some of the potential future directions identified include the need for effective research communication and strong cooperation between academia and relevant CC policy-making bodies to translate scientific research into evidence-based policies and actionable frameworks; tiered subsidies or tax rebates to low-income households to promote CC mitigating technologies and align CC objectives with social equity; and others. Although this work focuses solely on Nigeria, the country shares similar characteristics with many sub-Saharan African countries, and some others in the global South. Accordingly, the findings will be relevant to those areas, with some unique adaptations.

1. Introduction

Climate change (CC) is one of the most significant issues facing the world today. The recent climate changes are attributed to greenhouse gas (GHG) emissions produced by fossil fuel combustion. The energy consumption is driven by industrialization, urbanization and other socioeconomic activities [1]. Energy is critical to global and national socioeconomic development and growth. Thus, attention has been increasing on transitioning from fossilized energy systems to renewables and other technologies that reduce or avoid emissions [2]. However, one of the militating factors for GHG emission reduction in developing countries such as Nigeria is associated with the belief that they (developing countries) are responsible for a negligible amount of global emissions; and that energy consumption is crucial to their economic growth [3]. For example, Nigeria produces about 0.71% of global GHG emissions, accounting for 334 million metric tons of CO₂-e. This translates to around 1.6 tCO₂-e per capita. This positions Nigeria as the 161st country out of the 191 countries in the world based on per capita emissions. 62.4% of the emissions (208.4 mmtCO₂-e) comes from energy, while agriculture accounts for 24% (80.3 mmtCO₂-e) [4]. This relatively negligible emission (when compared to global emissions) and the need for energy to industrialize and meet the needs of the population becomes a major concern, especially for developing countries or the Global South where huge increases in industrialization, per capita GDP and huge population growth is fueling emerging economies. For example, a 1% increase in economic growth is shown to result in a 3.11% unit increase in carbon emissions in Nigeria [3]. Accordingly, it has been argued that emission reduction may decrease or slow down production, economic output and growth [5]. However, this perspective (positive relationship between emissions increase and economic growth) discounts the costs (short- and long-term) of climate changes impact on other areas of socio-economic development. This includes climate change-associated impact, such as disaster risk and extreme weather events, which adversely effects economic activities and the health burden from CC impact, with its associated impact on economic output, etc. This was demonstrated in a study which showed that, in an optimistic scenario, climate changes impact is estimated to reduce global economic output (GDP) by between 1.8 and 2.2%, while in a pessimistic scenario, economic output will reduce by 36% [6]. Globally, with average temperature increasing to 1.5 °C, CC-caused heat stress is estimated to affect more than 1 billion people, including about 350 million workers, if the temperature reaches 2.5 °C above pre-industrial levels [7]. Heat stress will affect the behavior and efficiency of the global workforce, and even lead to mortality [8]. Therefore, although many studies have shown that a unit increase in emissions increases global economic growth, in terms of GDP [8,9,10,11], they pose a serious socioeconomic and health implications for the global population.

In Nigeria, 7.3% and 4.2% increases in average temperature between 1988–1998 and 2011–2021, respectively, led to corresponding decreases in economic growth by −23.3% and −1.065%, respectively. Further, ceteris paribus, a percentage increase in average temperature decreases Nigerian economic growth by 0.67%. A percentage increase in precipitation is associated with a decrease of 0.23% in economic growth [12], while a 1% increase change in precipitation reduces agricultural productivity by 1.23% [13]. This indicates that although adequate precipitation is important for agricultural production, hydropower generation and water resources, increased precipitation, especially torrential rainfall and flooding, destroys infrastructure (transport, manufacturing, service, etc.,) and economic activity, resulting in extensive economic losses [12]. A 15% increase in CC-associated harmful degree days, HDD (degree days above 32 °C), reduces agricultural productivity by 5.22% and decreases income from crops by 0.52% (ceteris paribus) [13]. Similarly, a panel data study comprising 43 sub-Saharan African countries shows that a unit change in temperature leads to a decrease in GDP per capita by 0.0016% per annum. Nigeria, together with Sierra Leone, Senegal, Niger, Mauritania, etc., belongs to a group of high-risk countries where a unit temperature increase results in a decrease in GDP per capita by 0.0028% [14]. Nigeria’s large population, proximity to the coast, infrastructure deficit and governance are some of the factors that makes Nigeria at a high risk for CC impact [12,15]. Opposition to CC mitigation usually hinges on its costs, without considering its indirect cost. For example, economic losses from CC-caused heat stress may reach 1.5% of global GDP. On the other hand, by 2100, around 51.8% of global CC mitigation costs will be compensated by decreased losses in labor productivity, thereby benefiting the economy [16]. This supports the need for vigorous emission reduction and the pursuit of net-zero.

Although many developing countries in the Global South, such as Nigeria, contribute negligible amount of emissions, they are more vulnerable to CC for three major reasons. First, their major economic activities are in sectors, such as agriculture, which are heavily exposed to weather changes. Secondly, they tend to be in hotter or tropical settings. Thirdly, they have inadequate adaptive capacity, which is related to their technological and financial capacity and political will [6]. Nigeria, a coastal and tropical country, is facing impacts attributed to climate change. These include extreme weather and unexpected variations in temperature, flooding, displacement of people and destruction of farm lands [17]; delayed onset of rainfall and unpredictable dry spells, which may affect pest infestation and agricultural productivity [15]; increasing desertification and drought [14,18] and the erosion of coastal shorelines and loss of biodiversity [19].

Sustainable country development performance indicators on climate action show that Nigeria is ‘on track or maintaining SDG achievement’ in the area of ‘CO₂ emissions from fossil fuel combustion and cement production (tCO₂/capita)’ and ‘GHG emissions embodied in imports (tCO₂/capita)’. Nigeria ranks 146 out of 166 countries, with an SD index score of 54.5 [20]. Immense efforts are, therefore, required for Nigeria to achieve the pledged net-zero target by 2060. Decarbonizing the Nigerian economy is expected to have huge economic implications for the oil-dependent country. However, net-zero transition is expected to have a positive impact on the country in the long-run. Transitioning from an oil-dependent export economy will foster innovation in different areas of the economy. The shift will spur non-oil economic growth, as has been seen in vibrant Asian economies [21,22], leading to a better standard of living. Economic growth—as measured by GDP and higher income levels—fueled by technological innovation leads to a greater demand for environmental protection [10,23]. In addition to diversifying from an oil economy, CC mitigation measures will reduce Nigerian energy intensity (energy amount consumed to produce one unit of economic output). Lower energy intensity, an indicator of energy efficiency, is the result of an advanced level of service sector development [24]. Achieving emission reduction rates in line with the Paris Agreement and also maintaining economic growth is only possible through the rapid decarbonization of energy systems [23]. Accordingly, Nigeria has pledged in its nationally determined contributions (NDC) to reduce GHG emissions by 47% by the year 2030. Recently, the country passed into law the Climate Change Act (CCA) 2021, which aims to decrease GHG emissions and promote cleaner and sustainable growth. The Act established the Energy Transition Plan (ETP) to achieve its stated goals. The ETP targets the ‘expansion of gas generation capacity to establish baseload capacity for meeting increased electricity demand and integrating renewables’ [25]. While natural gas has a lower carbon footprint than some other fossil fuels, it still emits GHGs. Further, the issue of ‘stranded assets’ is one of the debated topics on achieving a clean energy transition [22]. Thus, there is a need to include other mitigation measures in other sectors of the economy apart from grid power generation. This entails the need for this work.

Many important studies have been carried out on climate change actions in different sectors of Nigeria. For example, Abam et al. [2] carried out a systematic literature review (SLR) on decarbonization in the Nigerian building sector, while comprehensive works on decarbonizing the Nigerian transport sector were conducted by Akujor et al. [26] and Dioha et al. [27]. Other studies included different pathways for Nigeria to achieve their climate goals [28], low-carbon transition and sustainable energy transition [29,30,31], low-carbon electricity systems [32], low carbon development in four critical sectors of Nigerian industry [33], decarbonization of the Nigerian power system [34], pathways to carbon neutrality for Nigeria [35], energy transition [22,36,37], low-carbon energy transition [38], sustainable energy transition [39], net-zero materials for carbon neutrality construction [40] and others. The present study tapped into the common themes (keywords) that have been used in previous studies on mitigating GHG emissions. The identified pertinent climate action keywords were used to conduct a search on the Scopus database in order to produce a holistic body of knowledge on ways to achieve emissions reduction, decarbonization or net-zero emissions. To the best of our knowledge, there has been no extensive research combining bibliometric, text mining and content analyses simultaneously in the research area spanning net-zero transition in Nigeria. Thus, the aim of this paper is to analyze the published literature (in the Scopus database) in order to uncover bibliometric trends, which include publication evolution, citation analysis, network (collaboration) analysis, data clustering between publications and authors’ keywords co-occurrence. The text-mining uncovers the major research themes and developments in the dataset (included articles), while the qualitative content analysis (CA) discusses the major clusters identified by the bibliographic clustering in detail. These will enrich the academic literature by developing a comprehensive research background. Accordingly, this paper reviews research works on climate change efforts with a particular focus on Nigeria. Specifically, the three research questions addressed in this study are as follows:

• How has the field of net-zero transition research evolved in Nigeria?
• What are the most important research themes and trends in research on the net-zero transition in Nigeria?
• What are the potential directions for future research or policy-making on the net-zero transition in Nigeria?

This study is necessary because by assessing studies carried out to achieve decarbonization, emission reduction, net-zero and related fields in Nigeria, major trends, themes and potential future directions will be uncovered. The body of knowledge/insight produced by the work will support future research developments and help with evidence-based policy/decision-making on ways to achieve climate change objectives in Nigeria.

The paper is organized as follows: the Section 1 provides an overall introduction, including the research aim and questions; while Section 2 discusses various climate change initiatives in Nigeria. In Section 3, the research methodology, selection, inclusion and exclusion criteria and data analysis are shown, while the Section 4 presents and discusses the study results in line with the research questions. In Section 5, the research implications (directions for future studies) are shown, while the conclusion is provided in Section 6.

2. Climate Change-Related Initiatives in Nigeria

This section discusses some of the critical initiatives in Nigeria for achieving emission reductions of net-zero in the country. They include the nationally determined contributions (NDC) under the Paris Agreement, Climate Change Act (CCA), Energy Transition Plan (ETP), Renewable Energy Policies Guidelines (REPG), Renewable Energy Action Plan (REAP) and National Biofuel Policy (NBP).

2.1. Nigeria’s Nationally Determined Contributions (NDCs)

Under the climate change regime in the Paris Agreement, a country-driven and bottom-up approach was adopted to establish countries’ climate change mitigation and adaptation commitments. Using this approach, the commitments agreed to by the parties (countries) are referred to as nationally determined contributions (NDCs). The NDCs are based on the individual countries’ conditions, resources and capabilities. In 2015, Nigeria set out to unconditionally reduce GHG emissions by 20% below the 2010 level and conditionally reduce them (subject to international support) by 45% below the 2010 level, by the year 2030 [41]. The difference between ‘unconditional’ and ‘conditional’ contributions was basically introduced for developing (or lower-income) countries. Accordingly, many developing countries presented two NDCs, referred to as ‘conditional’ and ‘unconditional’ targets [42]. Under the Paris Agreement, parties are obligated to submit a revised NDC by 2020. The updated NDC should progress further than the one given in 2015 [30,41]. In the revised NDCs submitted in 2021, Nigeria pledged, under the Paris Agreement, to fulfill a 20% unconditional reduction and increased its conditional commitment to a 47% reduction in GHG emissions by the year 2030. In the 2015 Nigeria NDCs, the major areas included ending gas flaring by 2030, the use of efficient gas generators, pursuing off-grid solar PV capacity of 13,000 MW, increasing energy efficiency by 2% per year (or 30% by year 2030), transitioning from cars to buses for transport, improving the electricity grid, climate-smart agriculture and reforestation [42]. Nigeria’s 2021 NDCs progressed from their 015 NDCs, improving climate ambition by adding new sectors (waste and water), and gases, short-lived chemical pollutants (SLCPs) and hydrofluorocarbons (HFCs) [43]. There are different views regarding the binding effect of the NDCs. While NDCs are voluntary commitments and their fulfillment does not essentially convey legal obligations, their incorporation into national laws makes them legally binding in the country [42]. Accordingly, the enforceability of climate change laws is based on NDCs.

2.2. Climate Change Act of 2021

Achieving the NDCs depends on governments (in this case, Nigeria) integrating these commitments into national policies, and Nigeria has the obligation of executing the agreed-upon measures (NDCs) at the national level. The most effective method to realize their incorporation is to embed the NDC targets within Nigerian national laws [42]. Therefore, to achieve these commitments on a national scale, the government of Nigeria enacted the Climate Change Act (CCA), which was signed into law in November 2021. Prior to the CCA 2021, the agreement was not enforceable because it was not domesticated in Nigerian law. The CCA 2021 is, therefore, a local enforcement tool for climate change goals in Nigeria. The Act established or introduced many mechanisms to achieve this, and they include (i) the National Council of Climate Change (NCCC), (ii) the Climate Change Fund, (iii) Carbon Tax and Carbon Emissions Trading, (iv) carbon budget, (v) the National Action Plan, (vi) climate change obligations and (vii) climate change education [44]. The Act establishes a basis for real climate action and provides means for climate change advocacy, and likely legal redress. It holds persons and entities liable for actions that impede the implementation of the climate mitigation and adaptation measures specified within the Act [45]. The Act extends the obligation of cutting emissions to both public and private organizations in Nigeria. It stipulates that private entities with 50 employees or more must put into place measures to reduce GHG emissions. Failure to do so will attract penalties, to be imposed by NCCC. Similarly, public entities, including ministries, departments and agencies (MDAs) are obligated to cut GHG emissions. In line with the Paris Agreement, which emphasized instituting and strengthening national institutions, the Act empowered the NCCC to help the government in achieving its commitments via policy formulation and decisions related to all areas of climate change in Nigeria. Climate change education, which mandates the incorporation of climate change in different educational fields and the national education curriculum at all levels, aligns with Article 12 of the Paris Agreement, which requires parties (member countries) to promote climate change education and involve their people at the local level [42].

Despite the lofty goals of the CCA 2021, it did not clearly include the 20% unconditional and 47% conditional emission reduction targets pledge made in Nigeria’s NDCs. Despite the absence of the emission reduction target in the CCA, the government of Nigeria is legally bound to achieve an unconditional reduction in emissions by 20% by the year 2030. This is due to the fact that an unconditional reduction in emissions by 20% is based on the principle of common but differentiated responsibility (CBDR). The principle of CBDR emphasizes that all nations shares the risks and adverse effects of climate change, requiring global collaboration to tackle it. However, the obligations or burdens of tackling the problems should be differentiated based on existing national conditions (either developing or developed). Further, the Sovereign Green Bond highlighted in the Act is at a relatively nascent stage. In 2019, after seven years, the Sovereign Green Bond was assessed at just NGN 15 billion (an exchange rate which was then USD 49 million). This is significantly negligible when compared to the estimated USD 304 billion required to achieve a 20% conditional emission reduction [42,43]. Furthermore, there are worries that the Green Bond funds may sometimes be redirected to non-green projects. Thus, section 4 of the Act, which specifies cooperation between the NCCC and the Nigeria Sovereign Green Bond, may not adequately pay attention to the actual measures required to achieve Nigeria’s NDCs [42]. Challenges militating against the success of Nigeria’s CCA also include corruption and financial mismanagement, poor institutional capacity, weak enforcement of environmental and oil-related laws and regulations, the poor political will of the government and poverty [45].

2.3. Nigeria’s Energy Transition Plan (ETP)

The ETP launched in 2022 is based on the Climate Change Act of 2021. The plan highlights the measures needed to achieve the net-zero target pledged by Nigeria in the country’s NDCs during COP26, while also meeting the country’s energy needs and delivering economic opportunities. The five sectors highlighted in the plan are power, cooking, oil and gas, transport and industry. Cumulatively, these sectors account for 65% of GHG emissions in Nigeria. The plan envisages that Nigeria will need to spend USD 1.9 trillion to achieve net-zero by 2060. A greater share of the funding (USD 405 billion) will be required to increase the generation and transmission capacity of the power sector. Also, transitioning to 90% renewables in the sector is expected to lead to significant savings (USD 121 billion) associated with the cost of fuel for generating power. These savings will compensate for the capital expenditure (CAPEX) increase. In the plan, the renewables needed in the power sector to achieve net-zero by 2060 include building 220,000 MW of solar, biomass and hydro-generation capacity, 90,000 MW of storage capacity and 34,000 MW of hydrogen system. The plan also includes a decentralized power system which includes solar micro-grids for both rural and urban areas which are interconnected to the grid (feed-in). In the oil and gas sector, minimal CAPEX spending is anticipated in the plan. The areas that will add cost in the sector are carbon capture and storage (CCS) application in refining and the expansion of gas infrastructure between the decades of the 2020s to 2030s. In the transport sector, the plan envisages that the transition to electric vehicles will achieve minimum differential or even cost parity with internal combustion engines, which will spur its increased adoption. Further, it anticipates that about 67% of transport will shift from passenger cares to buses (pooled transport), which will reduce emissions. In cooking, the transition from fuels such kerosene (DPK) to grid-supplied electric stoves is expected to reduce emissions and costs [25].

The successful implementation and achievement of the targets of Nigeria’s ETP within the stipulated timeframe faces many critical challenges. Financial capability (or fiscal constraints) and the economic (cost–benefit) implications associated with the transition pose a serious challenge for the practical achievability of the plan. The existing poor infrastructure and technological barriers impede the smooth integration of sustainable energy resources. Inadequate incentives caused by policy and ambiguous regulatory frameworks are further difficult barriers for the plan. Energy security, which relies on fossil fuel dependency, creates great reluctance toward the shift (energy transition) [46]. The increasing cost of electricity (resulting in more energy-efficient consumption) and cooking gas, caused by the gradual subsidy removal, will create a trade-off, causing lower income and rural households to return to traditional fuels such as firewood, with an attendant effect on deforestation. Thus, the trade-offs between different energy strategies need to be addressed.

2.4. National Biofuel Policy and Incentive (NBP)

Nigeria’s NBP, adopted in 2007, was made in pursuit of the government’s directive on the Automotive Biomass Program for Nigeria. Biofuels were envisaged to help meet the increasing demand for eco-friendly fuels that will reduce emissions, while supporting automotive, thermal and power generation. Biomass includes trees, crops, plant fiber, cellulose-based materials, industrial wastes and biodegradable constituents of municipal solid waste (MSW). Specifically, the biofuel feedstock emphasized in the policy are cassava, sugarcane, oil palm, Jatropha, cellulose-based resources and some other crops that may be agreed on by the Biofuel Energy Commission. The first stage of the program (intended to last for 3 years on a pilot basis and between 5 and 10 years for national roll-out) involved blending around 10% of ethanol fuel with gasoline (otherwise known as E-10). This was intended to last until Nigeria developed capacities to establish adequate biofuel plants and produce large-scale biofuel feedstock. In the second stage, the establishment of agricultural plantations and the construction of biofuel distilleries to support the E-10 blending was planned. Based on the country’s gasoline demand, this would require ethanol production of about 1.3 billion, increasing to 2 billion liters by 2020. Similarly, biodiesel production would need to be 900 million liters to enable 20% blending. The policy aims for domestic production of biofuels, and for the E-10 and E-20 blending to reach 100% by 2020 [47]. Unfortunately, none of these lofty targets have been achieved in the implementation phases. Except for the NNPC-conducted feasibility studies on bioethanol and biodiesel production, and the construction flag-off of 20 bioethanol plants with an additional 14 to follow later, there is limited information/data related to the policy implementation of NBP, making its evaluation scarce. Serious gaps include the policy’s emphasis on first-generation feedstock (edible crops) to address food security challenges in a country where millions lack food. The second generation focused on inedible crops and MSW, and the third generation focused on microorganisms and algae. Another gap is the inconsistency between the policy and various Nigerian agricultural policies [48].

2.5. Other Policies and Programs

The Nigeria Renewable Energy Master Plan (REMP) was produced in 2005. The plan is being implemented by the Federal Ministry of Environment, and aims to expand renewable energy (RE) to contribute 10% of total energy consumption by 2025; 23% of electricity generated by 2025; and 36% by 2036. Some of the specific targets to achieve these aims include installed capacities of small hydro-power (SHP), accounting for 600 MW by 2015, and rising to 2000 MW by 2025; solar PV, accounting for 500 MW by 2025; bioenergy power plants, accounting for 400 MW by 2025; and wind energy, accounting for 40 MW by 2025. While increasing RE adoption in the power sector, the plan also aims to increase electrification rates in Nigeria from 42% in 2005 to 60% in 2015 and 75% in 2025. Fiscal and market incentives targets to support the ramping-up of RE in the plan include an import duties freeze on RE technologies in the short-term. In the long-term, the plan recommends devising other tax credits, fiscal incentives and special loan schemes for RE projects [49]. The Renewable Energy Policy Guidelines (REPG) of 2006, similar to REMP, is a policy document by the Federal Ministry of Power that specifies policy goals for RE advancement and utilization. REPG places emphasis on RE generation and distribution, and charts a scheme for economical administration of the Renewable Electricity Trust Fund (RETF). The RETF aims to ‘promote, support and provide renewable electricity’ via private and public partnerships (PPP). Also, the policy targets international cooperation, such as in the clean development mechanism (CDM), knowledge-based networks (KBN) and others to achieve RE penetration and climate objectives [50].

The National Renewable Energy Action Plan (NREAP) of 2016 establishes the implementation strategy for the National Renewable Energy and Energy Efficiency Policy (NREEEP) of 2015. NREAP affords an outline of actual policy and regulations, laws, incentives and actions to be employed to accomplish Nigeria’s RE targets and Sustainable Energy for All (SE4ALL) goals. The NREAP includes targets for grid-connected and off-grid applications. These include increasing RE installed capacity to 9100 MW by 2030, with RE (excluding large- and medium-hydro) forming 28% of the total installed capacity by 2030, increasing the share of large- and medium-scale hydropower installed capacity to 4700 MW and others. The NREAP also includes onshore wind, solar (PV, thermal CSP), bioenergy, hydro, geothermal and others. NREAP envisions that 34% of Nigerian households will be using modern and cleaner cooking fuels such as LPG, biogas, solar and kerosene by 2030 [51]. Although kerosene (DPK) is relatively cleaner than solid fuels like charcoals, it emits relatively higher GHG emissions compared to LPG. Also, DPK emits a high level of fine particles (PM_2.5), leading to its classification as a polluting fuel by World Health Organization in 2014 [52].

Some of the gaps in these policies frameworks (NREAP, REPG, REMP) are the inconsistencies in the targets and timeframes, and targeted RE sources contributions. These inconsistencies create individual, but often conflicting, strategies. Thus, there needs to be a harmonization of policy directives (including targets, timeframes and others) to achieve holistic and extensive CC mitigation regimes. It is recognized that many of these were crafted before Nigeria’s initial and revised NDCs of 2015 and 2021 and the Climate Change Act of 2021. These policies should be subsumed or integrated into the Nigerian climate frameworks to enable the realization of CC goals.

3. Materials and Methods

A mixed method research design (qualitative and quantitative) was employed in this study. The process includes a literature search, assessment of the literature, and bibliographic review of selected papers. The selected papers were further analyzed. The search was conducted on the Scopus database. Scopus was chosen because it provides extensive and higher multidisciplinary and journal coverage than the WoS [53,54]. Scopus facilitates keyword query and citation analysis, resulting in the highest number of documents retrieved for bibliometric analysis compared to other reputable databases (Web of Science and PubMed) [54]. Scopus also includes content from specialized databases such as Embase, Compendex, Medline and others. Scopus is also more extensive than WoS in providing coverage for regional publications of all types [55], including African Journals Online (AJOL). AJOL is the largest online assemblage of African-published, peer-reviewed publications. More AJOL journals are indexed in Scopus compared to WoS [56]. Further, Scopus is the most comprehensive database of peer-reviewed literature. It features bibliographic data such as authors’ affiliation, country, year of publication, abstracts, keywords, etc. It also allows the retrieval of documents depending on the researchers’ choices [57,58]. This is unlike Google Scholar, which contains gray literature and whose features do not easily allow for the retrieval of documents [57]. Critical themes or keywords used to indicate climate change efforts were used to conduct the search on Scopus. These themes include decarbonization, low-carbon development (LCD) or low-carbon transition (LCT), net-zero emission, low-carbon energy, sustainable energy transition, carbon neutrality and others [1,39,57,59,60]. The search was conducted on the Scopus database on 29 February 2024 using the following Boolean strings: “decarbonization” OR “low carbon development” OR “low carbon transition” OR “low carbon energy” OR “sustainable energy transition” OR “carbon neutrality” OR “climate neutrality” OR “net-zero emission” AND “Nigeria”. The search returned 337 documents. The search result was then exported and saved as a .CSV file. To select suitable papers for the study, inclusion–exclusion criteria were applied as follows:

(i)

Exclude papers that are not written in English which the authors understand and are fluent in.

(ii)

Exclude papers on coal characteristics (such as physicochemical, thermogravimetric, etc.) This is because even though coal-to-gas shift (BTU) is touted as a climate-friendly transition, the coal gasification process has likely higher cost compared to natural gas [61], indicating its economic infeasibility in Nigeria, which has an enormous natural gas reserve and other potential renewables. Further, coal mining has numerous environmental impacts and has been abandoned for decades in Nigeria.

(iii)

Exclude papers on risk of pollutants such as hydrocarbons, etc., as they do not contribute to cutting GHG emissions or achieving net-zero.

(iv)

Include papers that focus on any of the relevant keyword items focused on Nigeria and those that combine Nigeria with other countries

(v)

Include papers on forestry and biomes carbon sink potential, as they pursue carbon sequestration.

Applying the inclusion–exclusion criteria to the title and abstract of the returned papers led to the disqualification of 138 papers. Data analysis was conducted on the remaining 199 papers. See the Supplementary Files for the included publications.

Data Analysis

Three analyses—bibliometric analysis, text mining and content analysis—were adopted in this paper to study the development and composition of the research area in Nigeria. The data analysis method, adapted from Ranjbari et al. [62] is shown in Figure 1.

Bibliometric analysis, a quantitative method and important statistical tool, enables the mapping of academic literature to determine future research trends within an area of enquiry. It achieves this by presenting a comprehensive imaging of connections between publications and their other features, such as source title (journals), keywords (authors’ or journals’ indexed-), citations and co-citations links [62]. VOSviewer software^® version 1.6.20 was used to perform both the bibliometric and text mining analysis. In the bibliometric analysis of the dataset (included studies), the following were investigated: the number of documents published in each year, the number of documents (articles, reviews, conferences and book chapters), the number of articles published by the identified journals and the number of citations garnered by the journals. Also, the top most-cited papers and journals they were published in, the most-cited and productive authors and the leading country and institutional affiliations of the authors were identified with the aid of the VOSviewer 1.6.20 software. Similarly, using the software, bibliographic coupling of the documents were performed. To obtain the significant papers, the minimum number of citations was changed from the default 0 to 10. A total of 61 out of the 199 documents met the threshold. The largest set of connected items was 41 documents, and these were mapped. The mapping yielded 8 clusters. Further, co-occurrence of authors’ keywords was performed to identify research hotspots. To achieve this, The VOSviewer’s default settings, ‘minimum number of occurrences of a keyword’, was changed from 5 to 2. Out of the 667 keywords, 105 met the threshold. Irrelevant items were removed, and 67 items were retained.

Text mining, an assemblage of statistics, machine learning and linguistics, enables the identification of patterns and trends in large unstructured (textual) data. The goal is to obtain quality information (text clustering, concept abstraction, etc.,) and to provide insights into a particular field [63]. A text mining technique on the co-occurrence algorithm for the nexus of the titles and abstracts of the included papers was used in this research. The text mining helped recognize themes and trends from net-zero transition publications in Nigeria. Out of the 6583 terms identified by the text-mining, only 109 met the VOSviewer’s default ‘minimum number of occurrences of a term’, which is 10. To capture a significant number of relevant terms, the default was changed to 5, and 296 terms met the threshold. The VOSviewer’s default mode of selecting the 60% most relevant terms means only 178 terms can be mapped. Further, 53 irrelevant terms such as ‘current study’, ‘presence’, ‘design methodology approach’, ‘originality value’ and others were removed, and 125 terms were retained. The mapping of the largest set of connected items generated 6 text-mining clusters. After carefully examining the terms included in each clusters, a common label connecting them was given to each cluster. Further, recent articles that have some of the terms in their titles and/or abstracts were then discussed to relate them to each generated text-mining cluster.

Content analysis (CA), a qualitative method, was performed as an additional and accompanied part. CA provides further support for the findings of the bibliometric and text mining analyses. In our study, bibliographic coupling networks between articles (data clustering) show clusters. Qualitative analysis was thereafter performed for the four most important publications (in terms of citations) within the clusters. From the 8 clusters generated by the bibliographic coupling of the documents, publications in each cluster were thoroughly examined to determine the common theme connecting them, based on their contents. Identification of the connecting theme for articles in each cluster informed the labeling of the cluster. The articles in each cluster were then qualitatively analyzed (discussed) to produce a body of knowledge, including identifying gaps and solutions for the net-zero transition in Nigeria.

To identify future directions, issues identified from discussing the articles in the clusters generated by bibliographic coupling analysis were used to proffer future directions. In this section, efforts were made to correlate or situate the issues generated in the clusters with broader climate policy frameworks in Nigeria, such as the Climate Change Act 2021, Nigeria’s Energy Transition Plan and National Biofuel Policy, etc.

4. Result and Discussion

4.1. Bibliometric Mapping of the Publications

This sub-section presents the bibliometric analysis, which addresses the first research question—how has the field of net-zero transitions research evolved in Nigeria?

4.1.1. Publications Evolution

Figure 2 shows the evolution of publications in terms of publication year, paper type, number of documents and citations from 2007 to 2024.

As shown in Figure 2, there is an increase in publications from 2015, with 87% of the papers (174 out of 199) being published after 2016. The lower numbers in 2024 may be related to the fact that the search was conducted in early 2024 (February). This, therefore, suggests a growth in publication rate from 2017 to 2024. A greater number of the publications were research articles (n = 126), followed by conference papers (n = 39) and book chapters (n = 21), while the least were ‘reviews’ (n = 12).

A total of 136 journals published the 199 papers included, starting from 2007 to 2024. Of the 136 journals, only 34 published at least two articles. The top 12 journals (in terms of number of publications) contain 44 out of the 199 items, representing 22% of the publications in the field. Three of the journals (Renewable Energy, Sustainability, IOP Conferences Series: Earth and Environment) published five papers each. However, Renewable and Sustainable Energy Review, which is second most productive journal in our dataset, has the highest citation number, representing an average of 99 citations per document, followed by Energy Report (52.6 citations per document) and Renewable Energy (4 citations per document), while the least is IOP Conference Series: Earth and Environment (0.4 citations per document).

4.1.2. Citation Analysis: Major Articles and Authors

The number of citations obtained by a publication is one of the measures indicating its impact in a research area [57,58]. The top ten most-cited publications within our dataset are shown in

Table 1. Top 10 most-cited papers within the dataset.

Rank	Authors	Paper Type	TC	TC/Y	Journal
1	Emodi et al. [64]	Article	180	25.7	Renew Sust Energy Rev
2	Mutezo and Mulopo [65]	Review	149	49.6	Renew Sust Energy Rev
3	Ndukwu [66]	Article	98	14	Renew Energy
4	Okundamiya et al. [67]	Article	81	20.2	Int J Hydrogen Energy
5	Farage et al. [68]	Article	75	4.4	Soil and Tillage Res
6	Akram [69]	Article	63	31.5	Energy Reports
7	Dillimono [70]	Article	55	6.1	Journal of Sustainable Tourism
8	Inal [71]	Article	52	26	Energy Reports
9	Akinyele [72]	Article	51	7.2	Renew Energy
10	Oyewo [73]	Article	48	8	Energy Conversion Manage

The average citations per journal (TC/Y) covering 2007–2023.

.

Twenty percent of the highly cited articles were published in Renewable and Sustainable Energy Reviews and Renewable Energy. This may indicate that the two journals are receptive to articles that focus on Nigeria’s climate change situations. The most-cited paper is an article titled ‘Energy policy for low carbon development in Nigeria: A LEAP model application’ by Emodi et al. [64]. The second most-cited article is a review, ‘Africa’s transition from fossil fuels to renewable energy using circular economy principles’ by Mutezo and Mulopo [65]. Ninety percent of the most-cited papers focus on energy. Although Emodi et al. [64] received the most citations, Mutezo and Mulopo [65], which is a more recent publication, has the highest citation average per year, followed by Akram et al. [69], while the lowest is Farage [68], which is the oldest paper in the dataset. Although the only review [65] in the top 10 cited papers has the highest average citations per year, 9 out of the 10 most-cited papers are research articles. Emodi et al. [64] used a long-range energy alternative planning (LEAP) model to evaluate the best scenarios to decrease GHG emissions in the medium-to-long range; Ndukwu et al. [66] used different scenarios to determine the optimum efficiency, energy conservation and CO₂ mitigation of a natural–convective solar dryer (NCSDR); Oyewo et al. [73] modeled different scenarios to evaluate a suitable cost-effective transition pathway for 100% renewable energy power system for Nigeria; and Okundamiya [67] used HOMER to evaluate the suitable hybridized RE mix. The oldest article in the dataset, Farage et al. [68], adopted organic soil models (CENTURY 4.0 and RothC-26 3) to evaluate the effects of changing agricultural practices on soil carbon sequestration potential. The most influential authors (number of citations) and most productive authors (number of publications) are shown in

Table 2. Most influential and productive authors within the dataset.

Most Influential Authors					Most Productive Authors
Rank	Author	TC	TP	TC/TP	Rank	Author	TP	TC	TC/TP
1	Emodi, N.V.	207	7	51.7	1	Dioha, M.O.	9	119	13.2
2	Emodi, A.S.	182	2	91	2	Emodi, N.V.	7	207	29.5
3	Emodi, C.C.	182	2	91	3	Kumar, A.	4	72	18
4	Murthy, G.P.	180	1	180	4	Adewuyi, O.B.	3	58	19.3
5	Mutezo, G.	149	1	149	5	Edomah, N.	3	46	15.3
6	Mulopo, J.	149	1	149	6	Ozdeser, H.	3	25	8.3
7	Dioha, M.O.	119	9	13.2	7	Seraj, M.	3	25	8.3
8	Ukoha, D.	98	1	98	8	Somoye, O.A.	3	25	8.3
9	Ndukwu, M.C.	98	1	98	9	Ohunakin, O.S.	3	16	5.3
10	Abam, F.I.	98	1	98
11	Eke, A.B.	98	1	98

TC (total citations). TP (total publications); listing of authors with at least three publications in the relevant areas.

.

Table 2 shows that Emodi, NV is the most influential authors with 207 citations, followed by Emodi, AS and Emodi, CC with 182 citations each. However, Dioha, MO with nine publications and Emodi, NV with seven publications are the most productive authors. It can be clearly seen that Emodi, N.V. and Dioha, M.O. appear in both lists of the most influential and productive authors, indicating their impact within the field in Nigeria.

4.1.3. Collaboration Analysis of the Countries and Institutions

The top contributing countries (country affiliations) of the researchers in the domain, net-zero transition in Nigeria and their linkages is shown in Figure 3.

In the VOSviewer map, the size of each circle indicates the number of publications emanating from the country. As shown in Figure 3, it is not surprising that Nigeria is the leading country in terms of the number of publications and total that relate to Nigeria. The next are the UK, South Africa, US, India and Australia, with 39, 18, 12, 12 and 11 publications, respectively. In terms of international collaboration, Nigeria, with 74 collaborations, is the highest, followed by the UK (39 collaborations), South Africa with 23 and the US with 21 links. On the other hand, China, with three collaborations, is the smallest established link among the top 10 countries of researchers contributing to the research field in Nigeria in our dataset. Overall, the links show the need for more collaboration between researchers within and outside Nigeria to advance research towards decarbonizing to net-zero in the country. The most productive institutions that published the articles are shown in

Table 3. Top seven most productive institutions to publish the articles within the dataset.

Rank	Organization	TP	TC *	TP/CP
1	Covenant Univ, Nigeria	13 (6.5%)	102 (2.6%)	7.8
2	Univ of Nigeria	11 (5.5%)	97 (2.5%)	8.8
3	Univ of Ibadan	10 (5.0%)	73 (1.9%)	7.3
4	Univ of Port Harcourt	7 (3.5%)	44 (1.1%)	6.3
4	Univ of Lagos	7 (3.5%)	46 (1.2%)	6.6
4	TERI Sch of Adv Studies, India	7 (3.5%)	108 (2.8%)	15.4
4	Obafemi Awolowo Univ	7 (3.5%)	25 (0.6%)	3.6
5	Univ of Johannesburg, SA	6 (3.0%)	23 (0.5%)	3.8
6	Federal Univ of Tech, Owerri	5 (2.5%)	17 (0.4%)	3.4
6	Michael Okpara Univ of Agric	5 (2.5%)	292 (7.5%)	58.4
7	Nisanti Univ, Turkey	4 (2.0%)	8 (0.2%)	2
7	Univ of Calabar	4 (2.0%)	21 (0.5%)	5.2
7	Landmark Univ	4 (2.0%)	48 (1.2%)	12
7	Univ Teknologi Malaysia	4 (2.0%)	23 (0.5%)	5.7

* 3856 citations have been generated by the 199 publications as of 29 February 2024.

, while Figure 4 shows their links.

As shown in Table 3, Covenant University is the most productive institution, having published the most articles within the field for Nigeria within the period. The University of Nigeria, with 11 publications, and the University of Ibadan, with 10 publications, are the next institutions. However, by number of citations, Michael Okpara University of Agriculture is the leading institution (292 citations). TERI School of Advanced Studies, India, with 108 citations, and Covenant University, with 102 citations, are the next.

4.1.4. Bibliographic Coupling: Data Clustering Analysis Between the Publications

Bibliometric analysis is a data grouping technique used to cluster items (articles) with similar characteristics from a sample to determine the research directions. Bibliographic coupling networks between articles reveal the number of cited references that is common to them [62,74]. To obtain the significant papers, the minimum number of citations was changed from the default 0 to 10. A total of 61 out of the 199 documents met the threshold. ‘The largest set of connected items’ was 41 documents (Supplementary File), which are mapped and shown in Figure 5. In our bibliographic coupling, eight clusters were generated. The top four articles in each cluster are shown in

Table 4. The top four most-cited publications within the major clusters in the dataset.

Cluster 1: Renewable energy, economic growth and emission reduction nexus	Akram et al. [69] İnal et al. [71] Voumik et al. [75] Bamidele et al. [76] * Somoye et al. [77] *
Cluster 2: Energy transition in Nigerian power system	Mutezo and Mulopo [65] Oyewo et al. [73] Yetano-Roche et al. [34] Owebor et al. [78]
Cluster 3: Policy drivers (socio-technical and economic) for a cleaner energy system	Emodi et al. [64] Adewuyi et al. [79] Barau et al. [80] Nwaiwu [81]
Cluster 4: ET governance	Edomah [36] Ebhota and Tabakov [82] Edomah [37] Daggash and Dowell [32]
Cluster 5: Hybrid renewable energy systems	Dufo-lopez et al. [83] Sofimieari et al. [84] Yakub et al. [85] Babatunde et al. [86]
Cluster 6: Low-carbon transition	Dioha and Kumar [27] Dioha and Kumar [29] Dioha and Kumar [30] Dioha et al. [31]
Cluster 7: Energy efficiency and low-carbon growth	Adom and Adams [87] Akinwale [88] Sarpong et al. [89] Akinyemi et al. [90]
Cluster 8: Solar PV mitigation potential	Akinyele et al. [72] Enongene et al. [91] Akinyele et al. [92] Tambari et al. [93]

* Two of them have equal citations, thus their selection.

. The label given to each of the eight clusters generated, shown in Figure 5 and presented in Table 4, was arrived at by finding the common theme uniting the publications.

In Section 4.3, QCA is conducted on the eight clusters and their four most important (in terms of citations) articles, as shown in Table 4. This will provide insights into their important themes and research directions.

4.1.5. Co-Occurrence of Authors’ Keywords: Identifying Recent Directions

Authors’ keywords in publications largely indicate the key ideas and areas of their research interests. Co-occurrence of authors’ keywords helps to pinpoint research epicenter in a certain domain [40]. The co-occurrence linkages of the authors’ keywords are shown in Figure 6.

The size of the circle is related to the frequency (occurrence) of the keyword item among the datasets. Accordingly, the larger the circle, the more the keyword items are mentioned or studied among the dataset. From Figure 6, it can be seen that ‘renewable energy’ has the biggest circle, followed by ‘energy transitions’, ‘sustainability’ and ‘energy efficiency’. This seems to indicate that this area attracts the greatest attention in pursuit of net-zero transition in Nigeria. The ten most common keywords and their link strength (TLS), respectively, are ‘renewable energy’ (27, 68), ‘energy transitions’ (21, 82), ‘sustainable development’ (12, 41), ‘sustainability’ (11, 26), ‘energy efficiency’ (10, 21), ‘energy policy’ (9, 26), ‘energy security’ (5, 17), ‘transport sector’ (4, 11), ‘energy consumption’ (4, 6), while there are three occurrences equally for ‘circular economy’, ‘low-carbon development’, ‘natural gas’, ‘sustainable energy’, ‘photovoltaic’, ‘carbon neutrality’, ‘decarbonization’, ‘biomass’, ‘waste management’ and ‘optimization’.

As seen in the map legend, many of the keywords range from green color to yellow, indicating that, on average, they are recent. In terms of publication year, keywords such as ‘leap model’, ‘energy forecasting’, ‘residential buildings’ and ‘electricity’ are older. Keywords such as ‘carbon neutrality’, ‘hydrogen’, ‘biomass’, ‘circular economy’, ‘electric vehicles’, ‘decarbonization’ and ‘net-zero’ are recent (yellow) by average publication year, indicating growing interest in the area. Ascertaining the most current functional research keywords within a research field helps researchers to pursue cutting-edge and interesting research, thereby advancing science [40]. Accordingly, the most recent keywords call for further research so as to advance the net-zero transition in Nigeria. It is interesting that many of these recent keywords, including carbon neutrality, net-zero, hydrogen and electric vehicles were well articulated in many Nigerian climate action policies such as Nigeria’s Energy Transition Plan (ETP). The plan aims to add an about 34 GW hydrogen system to Nigeria’s power system by 2060, and scaled penetration of electric vehicles (EVs) in the country due to its cost-effectiveness relative to traditional fossil-fueled vehicles [25]. All these are intended to help Nigeria achieve net-zero by 2060, according to the plan. The keywords ‘biomass’ and ‘circular economy’ align with various sectors and the waste sector, which was recently included in the revised Nigerian NDCs of 2021. These are envisaged in the Nigeria Circular Economy Roadmap and National Blue Economy Strategy, both launched in 2024. For example, an estimation showed that use of biomass (MSW) from a major city in Nigeria for energy production will help meet 12% of Nigeria’s REMP goal of 400 MW from WtE by 2025 [94]. Biogas produced from biomass and used for cooking was shown to reduce CO₂ emissions by 9.69 kg relative to LPG, 37.5 kg relative to kerosene and 181.65 kg relative to firewood [95]. The diversion of waste, including biomass, from landfill also reduces methane emissions [94], helping to achieve Nigeria’s climate goals, as envisioned in the revised NDCs of 2021 which included the waste sector. For hydrogen, a HOMER simulation showed that a hybrid system (hydrogen storage with PV/fuel cell) connected to the grid will cut CO₂ emissions by 97%, resulting in a cost saving of about 88% compared to the diesel/grid system and a 41% ROI [67], accordingly supporting Nigeria’s net-zero transition.

4.2. Text Mining Analysis: Uncovering Important Research Themes and Developments

The results presented in this section address the second research question—what are the most important research themes and trends for the net-zero transition in Nigeria?

The results of the text mining analysis show that existing publications in the field of net-zero transition in Nigeria centered on six major themes, as shown in

Table 5. Important themes within the dataset (net-zero transition in Nigeria).

Categorization of the Research Subject	Key Terms	Recent References
Buildings/residential	Building, carbon dioxide emission, carbon footprint, construction, consumer, economy, electricity, energy demand, energy use, global warming, greenhouse gas, household, kwh, low-carbon economy, negative impact, population, rural area, solar photovoltaic, sustainable development, utilization	[31,91,96,97,98,99]
Waste-to-Energy	Biomass, carbon neutrality, energy mix, energy sector, energy system, environmental impact, fuel, grid, hydrogen, infrastructure, integration, optimization, paradigm shift, power, power generation, renewable energy technology, technology, waste	[94,95,100,101,102]
Climate action	Climate action, climate change, climate change mitigation, community, contribution, deployment, economic development, energy access, energy policy, environment, framework, government, low-carbon, low-carbon development, opportunity, Paris Agreement, sustainable development, sustainable energy transition	[28,64,92,103,104,105,106]
Energy demand and consumption	Economic growth, energy consumption, energy source, environmental quality, financial development, implementation, long run, Nigerian government, policy implication, policymaker, renewable energy consumption, renewable energy source, short-run, stakeholder, urbanization	[5,38,69,71,107,108]
Energy transition	Clean energy, electricity generation, energy crisis, energy security, energy transition, prospect, renewable, renewable energy, sustainability, sustainable energy future, environmental sustainability	[22,79,93,109,110]
Carbon capture and others	Carbon capture, decarbonization, industry, net-zero, pathway, policy framework, storage	[2,26,34,35,111,112]

.

As shown in Table 5, the leading themes include buildings/residential sector carbon reduction, waste-to-energy, climate actions, energy demand and consumption, energy transition, carbon capture and other industrial technologies.

Housing and the residential sector emerged as one of the main research themes in the net-zero transition in Nigeria. This is because residences account for more than 80% of energy consumed in the country [99]. Buildings and the residential sector in Nigeria account for a total delivered primary and final energy consumption of about 2423 PJ and 26 million tons of CO₂-e. This emission is estimated to grow to 30.4 mtCO₂-e in the BAU scenario because of the use of a traditional biomass cook stove and inefficient energy appliances. The leading drivers of emissions caused by the energy demand of the sector are related to population growth, household income and urbanization. Further, poor architectural design increases the energy intensity of buildings and residences [113]. The carbon footprint of buildings is high due to the widespread use of fossil fuel generators because of poor power supply [97], presenting a significant challenge to decarbonization. Most of the research in this area focused on alternative energy supplies to reduce the carbon footprint [31,91,96,97,98,99]. Broader policy frameworks such as the Nigerian Climate Change Act 2021 impact the building and residential sector. This can be seen in various sections of the Act, such as S(20)(4)(b)(ii) which set ‘out actions for mainstreaming climate change responses into sector functions’; (vii) ‘to enhance energy conservation, efficiency and use of renewable energy in… domestic and other uses’ [114]. Accordingly, in the CCA 2021, the building/residential sector is required to pursue climate actions. In Table 5 (under the buildings/residential sector), key terms such as energy use, low-carbon economy, sustainable development and solar photovoltaic align with the identified themes in the CCA 2021 and Nigerian Energy Transition Plan (ETP). These include establishing a carbon budget, supporting energy efficiency and the use of renewable energy and sustainable development, which will reduce the carbon dioxide emissions and carbon footprint of the building/residential sector. In the ETP, power and cooking were identified as critical enablers to reduce emissions. The plan envisages transition to natural gas in the interim, and then in the long-term to renewable energy such as solar PVs and hydro, while for cooking, the transition from traditional fuels to grid-supplied electric stoves will decrease the sector’s emissions [25]. Other ‘mainstreaming climate change actions’ (envisaged in CCA 2021) in the building (built environment) sector include energy-efficient designs and sustainable/renewable energy and materials. The use of sustainable/renewable materials coupled with eco-design fits in with the Nigeria Circular Economy Roadmap (NCERM) [115]. All these accord with the Nigeria National Council on Climate Change (NCCC) long-term low-emission development strategy for the building and residential sector, which includes an extensive shift from traditional biomass use for cooking, the utilization of more energy-efficient electrical appliances (for cooking, lighting and cooling systems) and a greater emphasis on electricity so as to reduce the energy intensity of the sector [113]

The second is biomass and waste as a source of renewable energy. Waste sector accounted for 11% of Nigeria’s emission in Nigeria, accounting for emissions of around 48 mmtCO₂-eq in 2020. This is estimated to increase to 109 mmtCO₂ in the BAU scenario. This is associated with the poor waste management system in the country. Thus, in Nigeria’s long-term, low-emission strategy created by the NCCC, the circular economy and an improved waste management system are the two key leading areas for the waste sector. The circular economy includes waste-to-energy, which is only possible through developed waste management system [113]. The focus here is to improve environment quality through less emissions and pollution arising from the indiscriminate disposal of waste. Waste generation is increasing in the country due to the increased population and urbanization. The waste management system is still very weak and posits a big challenge to the country [94]. This contributes to the emission of greenhouse gases [100,102]. However, in the pursuit of climate management objectives and circular economy or bio-economy (CE or CBE) models, agro-wastes (lignocellulosic biomasses) may be used to produce bioethanol [102]; anaerobic digestion of vegetal wastes for biogas production [95]; biogas production from palm oil mill effluent (POME) and composting of fruit bunches from oil mills may decrease emissions by 66–75% [100]. Municipal solid wastes may help to generate about 59% of daily power requirements for some of the urban areas [94]. Techno-economic factors and the use of different bio-refinery systems to manage waste to produce biofuels and biodiesels were discussed by Igbokwe et al. [102]. These (waste-to-energy) align with Nigeria’s policy frameworks, such as the ETP which includes bioenergy as one of the renewable sources for achieving net-zero by 2060, and Nigeria’s National Biofuel Policy (NBP) of 2007 [48]. In the Nigeria’s NCCC strategy, the adoption of waste-to-energy, together with the only renewable energy scenario, is estimated to lead to emissions of 0.15 mmtCO₂-e by 2060 [113].

It is also noteworthy that the key terms identified in this theme—climate actions (in Table 5) such as ‘climate change mitigation’, ‘low-carbon’ or ‘low-carbon development’, ‘energy access’, ‘energy policy’, ‘sustainable energy transition’—fit in with many Nigerian frameworks, such as the CCA 2021 and ETP. Climate actions to mitigate or reduce emissions include either fiscal instruments or green fiscal policy mechanisms [106], sustainable agriculture, public education, improved waste management, CE [28], low-carbon development in the energy/power sector [64,103], and the pursuit of clean development mechanism (CDM) projects [92]. The country’s CCA 2021 is based on its NDCs including agriculture, waste and power in their commitment to conditionally reduce emissions. Similarly, the ETP calls for a low-carbon power system to push towards net-zero by 2060. Further, climate education was included in CCA 2021, which mandates the inclusion of climate change in the national education curriculum and various educational disciplines, and to involve people at the local level. Although CDM is not explicitly stated as a particular mechanism for achieving the goals in the CCA 2021 and ETP, an emphasis on internal strategy and international collaboration was indicated in both. In the ETP, mechanisms such as carbon market development and debt-for-clean energy were indicated. Accordingly, in Akinbusoye et al., it was emphasized that there is need for a strong institutional (legal) and governance framework [104], the decoupling of carbon emissions from energy security through pursuit of low-carbon energy development [105] and support for R&D on clean technologies [28].

Economic growth is correlated with energy consumption and carbon dioxide emissions [5,71,108]. The increasing urbanization in Nigeria implies higher demand for fossil fuels which impacts the environmental quality [5]. Easily et al. [107] emphasized the need for policymakers to develop policies and frameworks to accelerate renewable energy adoption. This is recognized in Nigeria’s CCA 2021 S(20)(5)(f), which provides ‘proposed incentives for private entities which achieve GHG emission reduction’ and S(21)(2)(j), which offers ‘incentives granted (to) private and public entities for their efforts towards transiting to clean energy and sustaining a reduction in GHG emissions’ [114]. However, while the critical need for incentives to accelerate technologies such as RE was indicated in the act, specific mechanisms to implement this should be explicitly detailed in associated policies. Others have advocated an optimum mix of fossilized and renewable energy to achieve economic growth [51,69]. A comparative legal analysis of Nigeria with China, Spain and Germany (countries with advanced RE systems) shows the need to reform Nigeria’s energy laws [38].

The inability of Nigeria to pursue energy transition hinges on its dependence on the petro-economy [22,77,116]. Accordingly, to promote energy transition, fiscal instruments, such as carbon tax, and financial incentives to consumers are necessary. Such programs will encourage cleaner energy and ease the transition to alternative energy [22,110]. Economic diversification (away from an oil-dependent economy) is important to achieve energy transition in Nigeria. This will help build financial capacity to invest in renewable energy [77]. The focus should not only be on cleaner energy, but also on energy security to prevent an energy crisis [87]. Energy transition pathways that assure energy security may include nuclear power plants for energy supply only [116], utility-scale solar PV and onshore wind [93], and utility-scale grid-connected VREs [79]. Adewuyi et al. [79] discussed the challenges facing Nigeria’s energy transition based on the experiences of more developed economies. Such challenges include the use of locally available energy resources to foster energy democratization, accelerated investment in a pumped hydro-energy storage system (PHESS), the electricity market and legal reforms [79]. The use of locally available energy resources aligns with both Nigeria’s ETP and the Presidential Compressed Natural Gas Initiative (PCNGI). While the ETP aims to connect to the grid about 197 GW of solar by 2050, both (ETP and PCNGi) emphasized the importance of natural gas as an abundant, ‘cheaper, cleaner, safer and more reliable domestically’ produced energy resource [117]. Because of the relatively lower cost of CNG compared to other vehicle fuels (PMS or AGO), CNG-fueled vehicles have relatively lower emissions and OPEX, a higher travel distance (fuel efficiency), potentially reduced maintenance costs and a suitable internal rate of return (IRR). The initial cost of CNG conversion kits and refueling stations are some of the issues facing its wide-scale adoption [118]. Thankfully, the Presidential CNG initiative addressed these concerns, as it provides free or heavily subsidized conversions for commercial (ride sharing) vehicles in Nigeria [117]. More could be done to provide financing mechanisms for private vehicle owners to transition to CNG. Also, the covered states and 1000 conversions workshop targeted by 2027 could be increased, to realize the deep emission cut potential of the initiative. To pursue a net-zero economy in Nigeria, research on the different pathways includes carbon capture storage (CCS) [34,111,112], while the decarbonization of the different sectors should focus on buildings [2], the cement industry [29,34], the transport sector [26] and carbon-neutral construction [40]. The transport sector accounts for 16% of Nigeria’s energy-related CO₂ emissions and industrial sector (4.6%) [113]. Demand management, CCS and the use of cleaner fuels are critical for emission-intense sectors such as the cement industry, where a ton of produced cement emits about 0.60–0.45 tons of carbon dioxide [34]. The cement industry alone emits 49.2% (8.3 mmtCO₂-e) of the emissions of the total industrial sector (17 mmtCO₂-e). Fortunately, CCS is recognized in Nigeria’s long-term low-emission strategy developed by the Nigeria’s NCCC. Specifically, the decarbonization and net-zero emission strategy aims at capturing 58% emissions from the cement industry by 2060, utilizing blending mineral substitutes and lower-carbon alternative fuels [113]. For CCS, the Niger Delta, with its small tectonic fault intensity and very large basin, makes the area a very good environment for CCS [112]. However, removal technologies such as DAC, CCUS and energy generation technologies (concentrating on solar panels, geothermal, nuclear and hydrogen) are still very poor in Nigeria. Conversely, for low-carbon systems such as hydro- and natural gas, which are already implemented in Nigeria, their adoption is very slow, even in the long-term [111]. Multi-level perspectives (political, economic, social, technological, legal and environment, PESTLE) show that there are a few drivers and challenges to carbon neutrality in Nigeria. The drivers are CC policies, global divestment from fossils fuels, difficulties with retrofitting ancient energy systems, available RE resources, carbon sink and bio-based potential [35]. The key terms identified on this theme align with existing climate change policies in the country, such as Nigeria’s Energy Transition Plan. The ETP emphasizes the significance of CCS as a means for net-zero transition, especially in the oil and gas industry, in order to achieve net-zero emissions by 2060. Similarly, the ETP highlights the importance of bioenergy with CCS (BECSS) [25]. While these ambitions are commendable, it is reported that the country is not ready for CCS in the near future. This is related to the huge cost of implementing it and improbability about the entire geologic storage potential in Nigeria. Increasing the forest cover in Nigeria via large-scale afforestation and reforestation schemes can provide a reliable, economical carbon sink in the short-term, while anticipating the development of CCS technology [119].

4.3. Qualitative Content Analysis of the Eight Clusters: Further Exploration

The bibliographic coupling generated eight clusters from our dataset. To carry out the QCA, the four most influential publications in each cluster were examined.

4.3.1. Cluster 1: Renewable Energy, Economic Growth and Emission Reduction Nexus

The most-cited articles within the time that constitutes this cluster on achieving CC goals are comparatively recent. Four of them were published in 2022, while one was published in 2023. All the articles within the clusters employed modeling methodologies. Three articles involved data consisting of many national blocks such as MINT [69], African oil-producing countries [71] and Africa’s ten most popular tourist destinations [75], while two articles were solely on Nigeria [76,77].

There is a disproportionate relationship between economic growth (EG) and environmental quality (including carbon emissions) in MINT countries. Low oil prices and industrialization negatively impact emissions [69]. A 1% increase in EG increases carbon emissions by 0.46%. This is because MINT countries, including Nigeria, are heavily dependent on fossil fuels to power economic growth. Energy efficiency is highly critical to a reduction in CO₂ emissions in MINT countries. Economic and population characteristics show that MINT countries will be among the global leaders in the next three decades. Nigeria will replace the US as the third most populous country by 2050. This economic and population growth entails huge energy demand, which can be met through energy efficiency (EE) and renewable energy (RE) [69]. In a fossilized energy system, the economic growth fueled by energy consumption for economic production means more emission due to higher energy intensity. Energy intensity (associated with energy efficiency (EE)) is the ratio of energy consumption to GDP [69]. Available data show that in 2021, the energy intensity per DGP in Nigeria was 6.6 MJ per USD. In 2000, it was 10.01 MJ per USD [120]. Increasing adoption of EE practices/technologies and RE will reduce further Nigeria’s energy intensity, even as the economy grows. A 1% positive change in renewable energy was shown to reduce carbon emissions by 0.85%, while a 1% increase in EE will reduce carbon emissions by 0.23% in MINT (including Nigeria) [69]. An increase in GDP was shown to promote RE adoption in Nigeria. A 1% increase in GDP increases RE consumption in Nigeria by 0.11%. Further, fossil fuel consumption and trade openness decreases RE consumption [77]. Akram et al. [69] shows that an increase in EG is associated with an increase in carbon emissions; the opposite is the case in Somoye et al. [77], which reveals that an increase in GDP increases RE consumption, which invariably lowers carbon emissions. The differences in findings on the relationship between the two works is methodological and/or sectorial. While the dependent variable in Akram et al. [69] is CO₂ emission, renewable energy consumption is the dependent variable in Somoye et al. [77]. In Akram et al. [69], the independent variables include renewable energy (RE) and energy efficiency (EE), measured by energy intensity, which is GDP per unit of energy use. On the other hand, in Somoye et al. [77], the independent variables were real GDP (RGDP), fossil fuel energy consumption (FEC), domestic credit provided by the private sector (DPS) and trade openness (TRADE). Thus, while Akram et al. [69] examined the influence of energy efficiency on CO₂ emission, Somoye et al. [77] examined the influence of economic factors, such as GDP and trade, on renewable energy consumption. There needs to be harmonization of the different methodologies or parameters to provide a clearer policy direction. The intermediate gap (or differences) between the two authors can be explained by the environmental Kuznets curve (EKC) hypothesis. As GDP increases steadily, carbon emissions will at first rise, but gradually fall. Carbon emissions will decrease as the government conceives and implements eco-friendly policies that reduces emission activities [75,76]. Regarding the positive relationship between GDP increases and RE consumption [75], there was no significant effect of RE on economic growth for Nigeria and other African oil-producing countries. This is because of the under-utilization of renewable energy potentials related to the high cost of RE production [71].

4.3.2. Cluster 2: Energy Transition in Nigerian Power System

The majority of the articles in this cluster are research articles, while one is a review paper. Three are recent (2020 to 2021), while one is more than six years old. The articles are on the concept and implementation pathways of ET and involve different outputs or resources. The review by Mutezo et al. [65] comprehensively discussed ET from fossil fuels to RE via circular economy approach in four sectors: manufacturing (using industrial symbiosis), logistics, bioenergy for electrification and waste management. They identified three drivers required for the transition: (i) policy drivers, including modern national energy policies, innovative fiscal instruments such as tax incentives, carbon tax and removal of fossil fuel subsidies (ii) technical drivers, namely efficient RE technologies which can be scaled and (iii) socio-economic drivers.

The following articles focused solely on power system (grid and off-grid) and include different resources in the energy mix, namely RE (solar and large hydropower) and natural gas [34], natural and syngas [78], RE (solar PV, wind, hydropower and bioenergy) and storage technologies [73]. Yetano Roche et al. [34] presented the different transition pathways to achieve Nigeria’s pledged NDC (decarbonization), access to electricity and renewable energy. The most ambitious scenario is the green transition scenario (GTS). This requires a 14.7% contribution of renewable energy, 28% use of natural gas, 5% use of large hydropower and 4% use of utility-scale solar power in the Nigerian energy mix by the year 2030. These scenarios will see emissions reduced by 146 to 153 MtCO₂e, helping Nigeria to meet its pledged NDCs.

4.3.3. Cluster 3: Policy Drivers (Socio-Technical and Economic) for a Cleaner Energy System

The four articles in this cluster are research articles. Two of the articles [79,81] indicated ‘sustainable energy transition(s)’ (SET) in their titles, while Emodi et al. [64] used ‘low-carbon development’. The articles addressed different policy issues that influence ET or uptake of low-carbon development and their policy implications. The four articles in the cluster identified the need for fiscal and legal instruments to scale a cleaner energy system. They include the socio-technical issues that inhibit the uptake of solar energy [80], digital technologies (blockchain, digital programs and smart grids) as enablers for innovative transitions in energy systems [81], energy justice (‘equitable right’) in the adoption of SET [79] and the effects of various energy policies under different scenarios on the Nigerian energy system [64]. Digitalization is an enabler of socially inclusive and environmentally sustainable energy production and consumption [81].

There is a divide between policy and industry attempts to adopt and employ digital technologies in Nigeria’s power system. This is attributed to a weak institutional framework. Nigeria is still at an early stage in the adoption and application of digital technologies. This absence greatly inhibits the operational characteristics of renewable energy systems such as tokenization and peer-to-peer trading of excess energy among energy-producing micro-grids. The absence of digitization leads to inefficiency and poor emissions tracking and reduction mechanisms [81]. Solar energy, which has great potential in Nigeria, is used mostly for lighting. The inadequate capacity limits its use for other household functions. Technical and maintenance issues, poor availability of skilled manpower, poor quality/shorter lifespan of the products (batteries, etc.,) in the Nigerian market are identified as issues affecting its uptake. Other issues include urban planning, which affects charging [80]; energy resource management (ERM), such as ‘gas-to-grid’; and WtE, which utilizes huge MSW and agro-waste to ensure energy justice and democratization. However, variable renewable energy deployment in Nigeria will be scaled only when reliability and profitability of RE technologies are established. These can be deepened by reduced import duties on RE, government sureties through fiscal and legal instruments and supportive restructurings in electricity market frameworks [79]. Policy implementation in the short-term can be addressed through energy-saving funds, such as clean development mechanisms (CDM) and global climate funds (GCF). This will help with the industrial transformation of the transport sector via CNG, LPG and a biomass-fueled transport system [64].

4.3.4. Cluster 4: Energy Transition Governance

In this cluster, two main domains were identified: governance in ET (Edomah [31,37] and issues associated with insights on how to deliver ET in Nigeria [82]. The fiscal challenges that face ETs was addressed in the study conducted by Daggash and Dowell [32], while Ebhota and Tabakov [82] discuss the importance of small hydropower (SHP) as opposed to large hydropower (LHP) in transitioning to a cleaner and sustainable energy system.

Four distinct eras in Nigerian energy governance are (i) grid-dependent (2005 and below) characterized by government ownership, (ii) self-generation, (iii) industrial energy outsourcing and (iv) industrial energy conservation. ET governance was shown to require both state and non-state (industrial) cooperation, and should foster energy democracy in terms of choice of energy supply, equipment and energy service companies, unlike the grid-dependent era [36]. Energy infrastructure preference is influenced by institutional forces and frameworks. The three major factors influencing ET and systems in the Nigerian electricity power sector are direct government involvements—the government provides energy infrastructure and important changes in market regulations. Since 2005, the liberalization of the electricity market has introduced the private sector into the power sector. The liberalization paved way for policies such as the Renewable Energy Policy Guideline (REPG), Renewable Action Program (REAP), National Biofuel Policy (NBP), etc., which support large-scale off-grid deployment systems and a diversified energy mix [37]. For example, the economic, technical and environmental benefits of SHP and the availability of around 270 ‘small rivers’ can be harnessed to generate about 734 MW electricity. There is, therefore, a need to rethink Nigeria’s hydropower projects [82]. Although distributed renewable energy systems such as SHP, solar, etc., democratizes energy investment, they seem costlier than conventional generation sources, such as large hydropower or natural gas. Accordingly, there is a need for renewable energy subsidies, carbon pricing (tax) and other solutions (CAPEX for renewable energy or low-carbon transition) to negate the poor macroeconomic issues that hinder low-carbon ETs [32].

4.3.5. Cluster 5: Hybrid Renewable Energy Systems (HRES)

The publications in this cluster used modeling software: HOMER [84,85,86] and hybrid optimization by genetic algorithm (HOGA) software [83]. HRES is playing a crucial role in the energy transition, CC mitigation and at the same time enabling off- and on-grid supply. However, their choice depends on techno-economic factors such as geography, etc., [62]. The various hybridization sources are PV/wind/diesel hybrid standalone micro-grids [84], PV–diesel and wind–diesel hybrid renewable energy systems [85], off-grid PV systems (PV generator + battery) with small demand electric cooking appliances [83] and PV modules + diesel generators + power converters and storage batteries [86]. Some of the technical factors include peak power capacity or peak load, daily energy capacity or power demand, supply duration, environmental health and sustainability [83,84,86], while the economic factors include LCOE, NPC (net present cost), O&M (operation and maintenance) cost [83,84], NPV [85], PBT (payback time) and replacement cost [84] and lifecycle assessment (emission (gCO₂)) of off-grid PV-powered system [83].

In numerous studies, a hybrid system was shown to reduce CO₂ emissions by 63% [84], between 64 and 74% reduction [86] and 25% reduction [83], respectively, and abated 73 tons of CO₂ emission [85]. The renewable portion was 83.1% [85], 95% [84] and between 70.2 and 90.1% [86]. With their simulated technical characteristics, the hybrid systems had an annual electricity production of between 4.6 and 5.4 MWh/year [86], 5.5 MWh/year [84] and 3.3 MWh/year [85], respectively. The LCOE was USD 1.07/kWh [84], and between 1.8 and 2.3/kWh [83]. Overall, the hybrid systems showed emission reduction and a reasonable LCOE, which indicates its economic performance.

4.3.6. Cluster 6: Low-Carbon Transition

Most of the articles in this cluster are research articles employing modeling methodologies and focusing on gas, a low-carbon energy source. Three of the articles were authored by Michael Dioha and Atul Kumar. Michael Dioha appeared in all the articles in the cluster. The authors’ country affiliation for the three articles are India, Nigeria and Australia. The TIMES model generator was used [27,29,30], while the Nigerian Energy Calculator 2050 (NECAL2050) was used in Dioha et al. [29]. All the articles in this cluster clearly show the role of RE, EE, natural gas and bioenergy in decarbonizing or LCT in Nigeria. The articles in the cluster address pathways for low-carbon transition in different sectors of Nigeria, including the land transport sector [27] and residential sector [30]. A multi-sectorial LCT (residential, industry, transport and commercial) energy system which includes both primary energy and electricity was assessed in Dioha and Kumar [29] while Dioha et al. [31] employed the input-wide-scale deployment of RE, nuclear energy, EE and low-carbon behavioral lifestyle to model pathways to low-carbon emissions in Nigeria.

From the articles in the cluster, the better fuel economy of vehicles and carbon tax will reduce CO₂ emission by 42.8% and 25.9%, respectively, in the year 2050. Despite the economic and population growth forecast which may lead to more vehicles, shifts to CNG and biofuels may significantly reduce CO₂ emission by about 12% in 2050 [27]. These aligns carbon tax and carbon emissions trading are envisaged in Nigeria’s Climate Change Act of 2021 [114], whose proceeds under management by the NCCC are meant to fund CC mitigation and adaptation objectives. Thus, these funds are a potential source to fund initiatives such as Nigeria’s PCNGI, which aims to incorporate CNG fuel (as an economic palliative and climate measure) for road transport. For example, in Dioha et al., an emission reduction of between 96 and 338 MtCO₂ can be achieved in the Nigerian power system through the adoption of different renewable energy sources in the energy mix. Also, sustainable consumption of residential sector will greatly advance energy efficiency and emission reduction [29]. This is because the energy demand of Nigerian households is expected to increase drastically from 2030 despite the adoption of renewable energy, energy efficiency and low-carbon behavior. This increase is fueled by economic and population growth [30,31]. Nonetheless, combining renewable energy adoption with energy efficiency (REE) will reduce CO₂ emissions by 8.1 MtCO₂ by 2050 [30]. In another study, penetration of combined high bio-energy, high energy efficiency and moderate renewable energy in Nigeria will lead to a lowest per capita GHG emission of around 0.77 tCO₂e/person by 2050. Under the current situation (conventional fossil energy system), emissions will be around 1.50 tCO₂e/person by 2050 [31].

4.3.7. Cluster 7: Energy Efficiency and Low-Carbon Growth

All the publications in this cluster are research articles. Three of them employed the following modeling tools: Computable General Equilibrium [90], Markov Switching Regression technique [87] and Data Envelopment Analysis [89]. In this cluster, two main domains were identified—energy efficiency [87,89] and low-carbon innovation/growth [88,90]. The route and challenges hindering escape from energy inefficiency in Nigeria were addressed by Adom and Adams [87], while Sarpong et al. [89] addressed the drivers of energy efficiency. The various factors responsible for energy-inefficient consumption in Nigeria include inept regulation, poor infrastructure (especially for energy and transport), poor institutional framework, pervasive corruption, widespread use of second-hand goods that are energy-inefficient, undeveloped markets, non-reflective tariffs in the energy sector and a high poverty rate [87]. Regarding poverty as a factor for inefficient and high-carbon practices, Dioha [119] emphasized that achieving Nigeria’s climate goals (both the ETP and those envisaged in the NDCs enforceable through the CCA 2021) first requires government breaking the continuous poverty circle. This, in turn, will increase the capacity of Nigerian citizens to purchase and adopt climate-friendly technologies [119]. High energy production efficiency and economic growth were associated with increase in adoption of energy efficiency. Poor industrialization in Nigeria (and other sub-Saharan African countries) means that their economies do not contribute substantial CO₂ emissions [89].

The importance of building capacity for indigenous low-carbon innovation in Nigeria instead of relying on technology transfers was addressed in Akinwale [88]. This is based on the problem of double externalities, market failures and the usual transfer of only hardware and not soft technologies capacities. The capabilities are initiated from government policies to foster collaboration (PP), R&D and investment/funding, prototype evolution, patenting and licensing contracts [88]. The government policies stimulating capacity building for low-carbon innovation are crucial since the much-touted subsidy removal and its associated drop and efficiency in fuel use will not produce the targeted carbon emission reduction. Local strategies such as fuel blending (envisioned in the National Biofuel Policy of 2007), CDM, green fiscal policies and green growth practices should be integrated to accelerate LC development [90].

4.3.8. Cluster 8: Solar PV Mitigation Potential

Relative to the other clusters, the articles in this cluster are older. Three of the articles were published before 2020. Different modeling tools were used: HOMER Pro [91], TIMES energy model and NECAL2020 [70], and the IEA Photovoltaic Power System (IEA-PVPS) Task 12 [72]. The four articles in this cluster focused on the potential of the solar PV system to mitigate CC or reduce carbon emissions. The focus of the articles include lifecycle impact assessment of PV power generation [72], the potential (environmental and economic) of solar PV for residential sectors in a major urban area of Nigeria [91], the possibility of deploying small-scale solar PV systems in Nigeria through the clean development mechanism (CDM) and the significant role of utility-scale solar PV among other renewable energy for sustainable electricity supply in Nigeria [92].

Solar PV emission reduction potential in Nigeria varies from 7.5 tCO₂eq/yr (tenement building) to 2.1 tCO₂eq/yr for duplexes. On the average, the use of solar PV-generated electricity reduces emissions from the residential sector by around 63.2% per annum compared to supplies from the grid, fueled by mostly natural gas. However, the cost (LCOE) of solar PV systems, ranging from 0.4 to 0.7 USD/kWh, is higher than that of the grid (0.09 USD/kWh) [91]. Financial cost is a huge impediment to the wide-scale adoption of a solar PV system in Nigeria. However, CDM funding has been touted as one way to deploy huge solar PV in the country [92]. The PV has a lifecycle GHG emission of 37.3–72.2 gCO₂eq/kWh, which is significantly low compared to natural gas (499 gCO₂/kWh) and diesel (763 gCO₂/kWh). The global warming potential (GWP) of PV in the six geographical locations of Nigeria ranges from 318 to 916 kgCO₂-eq. Comparatively, the total emission produced by a solar PV system during its 25-years lifespan equals the emission generated by a 1.5 kVA diesel generator in one year [72]. Utility-scale solar is the most favorable method to transition to 100% renewable electricity supply in Nigeria by 2050. Around 479–780 GW of PV is required to achieve this. Around 9.3 m² is required for each 1 kW of solar PV. There is, therefore, a critical issue of land availability to situate large-scale or utility-scale solar PV for 100% renewable transition in Nigeria [93]. One of the important conditions to be fulfilled for a project to be adopted as a CDM project is that the project achieves GHG reduction, which would otherwise be impossible without the project existence [92].

5. Research Implications: Further Directions

From the conceptions and understandings furnished by the bibliometric analysis, text mining and QCA, implications for future research are discussed in this section to tackle the third research question—what are the potential directions for future research or policy-making on pursuing decarbonization to achieve net-zero emissions in Nigeria? From our analysis, to suitably cut emissions while pursuing net-zero emissions in line with Nigeria’s climate goals, the following are the future directions.

One of the major implications of this study is the importance of bridging the gap between academic research and practical implementation (emission reduction or net-zero strategies). This entails evidence-based policy-making. However, different research methodologies may lead to seemingly contrasting findings, further confusing the targeted audience of populace and policymakers. This is seen, for example, in the first cluster (Section 4.3.1), where there seemingly was a disparity in the findings of Akram et al. [69] and Somoye et al. [77]. This difference is methodological, involving different parameters (independent and dependent variables). Accordingly, there is need for a coherent, effective communication of research to provide clearer policy directions for policymakers on the relationships or factors at play between various variables. Thus, there is a need for synergy and effective research communications to convey to the public and policymakers (who may not be familiar with technical terms) suitable policies. Effective research communication involves clarity, conciseness and accessibility. Similarly, there needs to be a vibrant and strong liaison between the different policy actors and academia. Thankfully, the Climate Change Act created the National Council of Climate Change (NCCC), while the Energy Transition Plan created the Energy Transition Office (ETO) under the office of the Vice-President. Both are tasked with coordinating implementation, collaborating and mainstreaming their intended targets, while the NCCC is charged further with ‘legislative, policy and other CC mitigation and adaptation measures recommendation’. Thus, academia, through organizations, think tanks, public forums or research grants, should be integrated into these policies’ implementation to facilitate the sharing of sound and robust data findings and actualize Nigeria’s climate change targets.

In cluster 4 (energy transition governance), the removal of fossil fuel subsidies to create cost-effective economics for RE was shown to foster ET systems in Nigeria [32]. The removal has significantly increased the cost of fossil fuels, including cooking gas, AGO and PMS. However, the micro- and macro-economic implications are impacting the economics (operating and earnings) of enterprises and households. This is more crucial, as Edomah [36] shows that ET in Nigeria is shifting energy infrastructure governance away from public to private interests, where profitability is paramount. The privatized energy market and removal of fossil subsidies, therefore, portends serious socioeconomic and environmental implications for millions of Nigerians who earn less than USD 1 a day. The trade-offs mean many low-income households (rural and urban) may shift to fuelwood, increasing the deforestation rate. The inconclusiveness and fragmentation of the literature connected to the environmental effects of removing the fossil fuel subsidy, together with their methodological deficits, affects policy-making. Notwithstanding the adverse economic impacts of the removal, it can be eased via government payment transfers to businesses and households. This is supported by the African Energy and Environment Integrated Computable General Equilibrium (AEEICGE) model, which shows that the reallocation increases the fiscal welfare and carbon abatement capability of firms and households by between NGN 16 billion and NGN 79 billion [121]. Further, fossil fuel subsidies removal has been identified as a feasible path to achieving net-zero in Nigeria by considerably lowering the country’s carbon emissions due to the reduction in fossil fuel consumption. This will create a more favorable environment for investment in RE sources, and the reinvestment of the removed subsidy revenue in green infrastructure projects [32,65]. There is, therefore, a need for a practical (not rhetorical) policy mix to address these trade-offs that ET will foster, or already is fostering, in Nigeria. Some of the concrete measures to address this include tiered subsidies to reduce the upfront or initial investment cost for solar PV systems, tax rebates or financial incentives for low-income households who adopt solar PVs. This will align the pursuit of climate change objectives with social equity. Others include collaboration with financial institutions to provide low-interest long-term loans offering flexible payment plans, shared large-scale solar developments which provide the advantage of economic scale and reduced initial investment costs for investing households. The financing could come from, for example, the Nigeria Climate Change Fund (under the CCA 2021) or other green development mechanisms. This aligns with the CCA 2021, S15(2)(f)—‘funding innovative climate change mitigation and adaptation project…’ and S15(2)(j) ‘incentivizing private and public entities for their efforts towards transitioning to clean energy and sustaining a reduction in GHG emissions’ [114]. In another vein, digitalization was shown to help achieve major disruptive transformations in ET [81]. However, Nigeria is still at an early stage in digitalized energy systems, such as blockchain and smart grids. Accordingly, more applied research is required in the area to scale disruptive ET in Nigeria. As discussed in cluster 8, (Section 4.3.8), the important role of solar PV in achieving a decarbonized energy system (cluster 8) cannot be overemphasized. However, the huge initial capital cost has limited its wide adoption in Nigeria. Its intermittency and requirement for storage (especially for the grid) necessitates another huge investment. Research directed towards cost-effective models with different ownership patterns and the policy drivers needed to accelerate them is required. This is necessary as governance structures dictate the economics of energy systems [36,82], which is critical for a developing country such as Nigeria. The direction should factor in the critical aspect of economics of scale (private collective ownership in scales such as community, neighborhoods, etc.) to drive deep penetration of solar PV systems.

As shown in Figure 6, there are some objects of interest in net-zero transition. They include hydrogen, biomass, the circular economy and electric vehicles. However, research needs to address policy drivers, technological and process developments and market incentives in the country’s ET program. Methodological approaches to assess the viability and scalability of emerging technologies such as hydrogen systems and EVs in Nigeria should include (i) market analysis, including demand forecasting, targeted consumer segments based on their socioeconomic status and pro-environmental behaviors; (ii) feasibility (techno-economic and social) studies, including evaluation of cost and availability of EV spare parts, the environmental and economic perception of EVs among Nigeria populace and cost–benefit analysis of adopting EVs compared to traditional fossil-fueled vehicles (iii) infrastructure evaluations, which should include the availability/accessibility of charging stations and their reliability, capacity of the grid or power network to manage the increased electricity demand for EV charging, availability of spare parts and trained technicians for EV repair services and (iv) policy analysis to identify the opportunities, challenges and gaps in extant regulatory framework and government support (such as incentives and infrastructural investments to scale its adoption).

Biomass and the circular economy offer the use or valorization of bio-wastes for energy production. However, recovering the generated waste (logistics), which requires robust data and funding, is a major challenge. This is supported by many studies which show that reliable data on waste generation, collection and others is at best lacking/inadequate in Nigeria [94,101]. This is supported by the Sustainable Development Report, which identified unavailable information as a challenge for municipal solid waste (kg/capita/day) and e-waste under the indicator ‘Responsible Consumption and Production’ [20]. Similarly, the environmental and socio-economic trade-offs associated with growing crops for bioenergy (food versus energy conflict), in a country with a high level of poverty needs to be addressed. Thus, there is a need for a robust, effective and low-carbon logistical system that will enable the valorization of waste. Furthermore, there should be a tradeoff between food security and the conversion of crops for energy purposes. There is a need for research on the role of CE in decarbonizing the economy. There is interest in research on electric vehicles; however, there are issues of adopting, such since problems arise with the scarcity of charging stations [122]. While Nigeria’s Energy Transition Plan has an ambitious goal of achieving 60% electric vehicle adoption by 2050 and 100% adoption by 2060, the socioeconomic and technical modalities needed to promote its market viability are lacking. The Presidential Compressed Natural Gas Initiative (PCNGI or Pi-CNG), a palliative measure aimed at providing relief for the high cost of living caused by the subsidy removal on petroleum motor spirit (PMS), is commendable. Critical development of the strategy across its value chain will capitalize on Nigeria’s abundant natural gas reserve and foster a shift away from gas flaring. This will significantly help to reduce emissions in the oil industry and the vigorous pursuit of one of the unconditional elements of Nigeria’s revised NDC of 2021 aiming at ending gas flaring by 2030. This is possible only if the required investment is made. CNG, a cleaner fuel, is favorable in the intermediate stage, but to achieve 100% zero-emission in the transport sector, there needs to be a consistent harmonization between the different strategies. Although CNG emits significantly lower CO₂ (and thus lesser GHGs emissions) than PMS or AGO when combusted, its value chain (production and delivery) and leakages may emit methane, a potent and short-lived GHG, that has 28 times the warming effect of CO₂ over a 100-year period.

6. Conclusions

This research adopted a mixed method of qualitative and quantitative analysis by using bibliometric methods, text mining and QCA to present a comprehensive representation of research on net-zero transition in Nigeria. The specific objectives are: (i) identifying how this field of research has evolved in Nigeria, (ii) identifying the most important research themes and trends of net-zero transition in Nigeria, and (iii) identifying the potential directions for future research. A literature search was conducted in the SCOPUS database using relevant Boolean operators. Exclusion–inclusion criteria were applied. Eighty-seven percent of the publications in our dataset were published from 2016 to 2024, indicating growing interest in the field. 63.3% of the publications in our dataset are articles and 19.6% are conference proceedings publications. The co-occurrence of authors’ keywords appears to indicate that ‘renewable energy’ is the most focused-on term in the pursuit to net-zero transition in Nigeria. This is followed by ‘energy transitions’, ‘sustainability’ and ‘energy efficiency’. Eight clusters of articles were identified: (i) intersection between renewable energy, economic growth and emission reduction (ii) energy transition in the Nigerian power system, (iii) policy drivers (socio-technical and economic) for a cleaner energy system, (iv) energy transition governance, (v) hybrid renewable energy systems, (vi) low-carbon transition, (vii) energy efficiency and low-carbon growth and (viii) solar PV mitigation potential. The major themes that were identified are: (i) buildings/residential, (ii) waste-to-energy, (iii) climate actions, (iv) energy demand and consumption, (v) energy transition, (vi) carbon capture and others. The co-occurrence of authors’ recent keywords are: ‘carbon neutrality’, ‘hydrogen’, ‘biomass’, ‘circular economy’, ‘electric vehicles’, ‘decarbonization’, ‘net-zero’. Some of the identified potential future directions include the need for effective research communication and collaboration between academia and pertinent climate change-saddled entities to promote evidence-based policies and mainstreaming of these into the actionable frameworks. Other directions are tiered subsidies or tax rebates to low-income households who adopt CC-mitigating technologies such as solar PVs, in order to align climate change objectives with social equity. The study also called for a methodological approach to assess the viability and scalability. This includes market analysis, techno-economic and social feasibility studies of emerging technologies such as hydrogen and EVs in Nigeria; infrastructure evaluations to support such systems; and policy analysis to identify gaps and opportunities for better policy-making.

7. Limitations of the Study

This study acknowledges limitation because only the Scopus database was used. In the future, accessing and retrieving samples from other reputable databases such as Web of Science (WoS) and Science Direct could make more datasets available for bibliometric, text-mining and content analysis on the research field, climate change initiatives in Nigeria.