Sectoral Contributions to Carbon Dioxide Equivalent Emissions in the Nigerian Economy

In line with the Intergovernmental Panel on Climate Change (IPCC), we estimate the percentage carbon dioxide equivalent (CO2-eq) emissions by sector in Nigeria. In terms of its emissions, the percentage contribution of carbon dioxide, CH4 and N2O to each sector were considered using the 2006 IPCC emission calculation default taking 2012 as the base year projected to 2027. Results revealed that, fugitive emissions from oil and gas accounted for the highest contribution to CO2-eq emissions with about 75.27% when compared to other sectors. This is due to increased gas flaring employed to dispose of associated gas in major petroleum/oil producing areas in the country. This sector pollutes because of their technology, the remaining sectors were identified as important sectors because of the weight they have on the economy. The study suggests the need for Nigerian government to ensure the security of fuel source for power generation by mandating oil companies to channel their flared gases to power plant.


INTRODUCTION
From available literature, the increase in population couple with higher living standards which invariably triples the demand for sectors which uses more energy like electricity, transport, petroleum etc., are responsible for the persistent increase in the emission of greenhouse gases (GHGs) in Nigeria (Federal Republic of Nigeria, 2014).
As part of measures towards mitigating these global carbon emissions, the federal government was among the other countries who ratified the Paris agreement geared towards ensuring a rapid and climate smart development. Similarly, the Kyoto protocol to the United Nations Framework Convention on Climate Change (UNFCCC) founded in Japan geared towards the stabilization of GHG concentrations in the atmosphere was revalidated with actions in 2005, with 192 parties to this protocol who ratified it as of June 2013 (Sulaiman et al., 2014). In addition, Nigeria has been registered as a member country of the United Nations Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation (UN-REDD), Clean Development Mechanism (CDM) projects, Clean Technology Fund (CTF) of which the World Bank is the trustee (Henrich, 2012b) and the Global Energy Efficiency and Renewable Energy Fund (GEEREF) of the European Union (Gereef, 2012), United States Trade and Development Agency (USTDA), Nigerian Electricity Regulatory Commission (NERC). These amongst other projects were geared towards cutting emissions, not only in the Niger Delta (Ogoniland), but also tackle the problem of drought and desertification in the northern areas. Despite all these measures, GHG emission is still high due to inadequate commitment towards sectoral contributions and their projections.
in Mexico (Chatellier-Lorentzen and Sheinbaum-Pardo, 2017), Beijing (Lixiao et al., 2014), Brazil (Imori and Guilhoto, 2010), China (Lin and Xie, 2016), Uruguay (Piaggio et al., 2014) and Spain (Alcántara and Padilla, 2006) but dearth is evident in Nigeria, even when she is known to be one of the largest emitter of GHG in Africa (World Resources Institute, 2010). This study employed the Intergovernmental Panel on Climate Change (IPCC) methodology for computing GHG emissions with emphasis on determining sectoral contributions to carbon dioxide equivalent (CO 2 -eq) emissions in Nigeria (Intergovernmental Panel on Climate Change (IPCC), 2006).

Data Sources
The study adopted secondary data for its analyses. The contribution of each anthropogenic gases (taking into consideration carbon dioxide [CO 2 ], CH 4 and N 2 O) were calculated based on 2006 IPCC default taking 2012 as the base year projected to 2027.

Data Analysis
The data for this study was calculated based on the 2006 IPCC for national GHG inventories, as presented in Table 1.

Model Specification
In line with the IPCC emission sectors description, thirty (30) sectors were identified as emission driven sectors in Nigeria from where their emission levels were calculated. The general approach in the estimation of GHG emissions level for CO 2 , CH 4 and N 2 O were based on 2006 IPCC guidelines, Vol. 4, Ch. 10 and 11, whose formula is presented as:  (Table 1a), N T = Number of heads for animal in category T, T = Animal category.

RESULTS AND DISCUSSIONS
Estimates of percentage CO 2 -eq emissions was calculated based on the 2006 IPCC methodology guidelines. Based on available information adopted from the IPCC, the CO 2 , CH 4 and N 2 O emissions was calculated for 2012, taking 2012 has the base year projected to 2027 (15 years). Table 2a and b, about 15 sectors subsumed into the energy and industrial processess were identified to contribute to CO 2 emissions in the country. Total CO 2 emissions of 416,035 Gg accounting for the highest contributions was emitted from the road transportation sector followed by fugitive emissions from oil/gas sector with a total emissions of 374,347 Gg. The link between CO 2 emissions and transportation arises as a result of emissions by the various modes of transportation which contribute to global warming and climate change. According to IEA (2014) Public electricity and heat production 1A1bc

As presented in
Other energy industries 1A2 Manufacturing industries and construction 1A3b Road transportation 1A3c Rail transportation 1A3d Inland navigation 1A3e Other transportation 1A4 Residential and other sectors 1B1 Fugitive emissions from solid fuels 1B2 Fugitive emissions from oil and gas 2A1 Cement production 2A7 Production of other minerals 2B Production of chemicals  (Chukwu et al., 2015).
The study carried out by Maceij et al., (2017), revealed that road transport influences air quality in Nigeria. This applies to the cities (especially the thickly populated cities) where there is a large movement of cars, which are often old and do not meet current environmental standards. The noise and carbon-monoxide emissions from the road transportation sector create direct and harmful effects on the environment, along with indirect impacts. According to Onokala (2015), the road transportation contributes significantly to the socio-economic development in Nigeria as it creates new lands for agricultural, industrial and residential development. However, despite the fact that roads changed the orientation of the interior areas of the country from the waterways and the railways to the road network, and its flexibility creates openness/accessibility to the interior parts of the country, as well as employment opportunities to drivers, mechanics thus raising economic standards, its resultant effects in the emission of GHGs cannot be overemphasized.
In a similar study carried out by Daramola (2018), his study revealed that the transport sector is responsible for 23% of energy  related CO 2 emissions and 13% of GHGs globally. However, Onokala and Ali (2010) examined the potential contribution of sustainable urban transportation in the reduction of GHG emissions in Nigeria and recommended the use of the methods of Sustainable Transport defined as all forms of transport which minimize fuel consumptions and emissions of CO 2 and pollutants. These methods can reduce traffic congestion and volume of vehicles on the roads.
Similarly, the unsafe practices and non-maintenance of refineries with the oilfields in the Niger Delta Anomohanran (2012) connected for the transportation of petroleum products from the refineries to the NNPC pumping stations and depots across Nigeria has led to about 18.59% contributions from fugitive emissions from oil and gas sector to CO 2 emissions, thus, suggests the need for existing pipelines to be put back into use and also expanded to other neighboring countries so that Nigeria not only supply petroleum products to them and earn some foreign exchange, but also tankers would no longer be used for long distance transportation of petroleum products in the country. Also, in the study, rail transportation and inland navigation were identified to have one of the least contributions to CO 2 emissions. This suggests that effective mitigation options through the construction of an entirely new railway network across the 36 states of the federation and the development of navigation aids for transportation in riverine communities so that such rivers can function efficiently as waterways for transportation in the country is vital.  As presented in Table 3a and b, the fugitive emissions from oil and gas accounted for the highest (49,495 Gg) methane emissions followed by enteric fermentation from the agricultural sector the when compared to other sectors. This could be as a result of CO 2 from liming and urea application, burning of agricultural residues and savanna for land clearing. However, the use of compost has been known to mitigate these emissions. Compost and related products are obtained from recycled organic materials comprising garden and food organics, crop residues, biosolids and manures.
However, the Environmental Protection Agency (2012), identified domesticated ruminant livestock, like cattle, sheep and goats as the greatest agricultural source of methane. From the report, methane was identified to be produced by bacteria in the animal's digestive system that break down fibrous food, which is later released as methane gas into the atmosphere mainly through its mouth and nostrils. However, when these materials are diverted from landfill, methane emissions would be reduced to barest (Table 4). In addition, the application of the products can also help to mitigate climate change through carbon sequestration in the soil, water holding capacity and substitution of nitrogenous and other synthetic fertilizers.
Also, the burning of associated gas in oil fields and overdependence on oil as the major source of revenue in the country  could be associated with the increase in fugitive emissions from oil/gas sector, thus, suggests the need for Nigeria to look beyond oil/reduce economic dependence from the oil sector and adopt other revenue sources from agricultural exports, entertainment/ tourism, diversification, liberalization, reshaping our political system, design an automobile policy that encourages the use of electric cars, improve fiscal sustainability over time, in order to ensure sustainable development and shared prosperity in the economy.
As presented in Table 5a and 5b, manure in pasture, range and paddock from the agricultural sector in addition to the emissions from the residential and other sectors accounted for the highest nitrous oxide emissions (with 1013 and 251 Gg respectively) in the country when compared with other sectors. This arises as the a result of increased numbers of livestock and high population growth rate with corresponding increase in per capita energy and other resource consumption. The deposition of manure and urine in the soil by farm animals, increases the emissions of N 2 O. According to Cha and Igbokwe (2012), cattle rearing alone generate more global warming GHGs, as measured in CO 2 -eq, than transportation. Stephen (2014) in a similar study added that livestock population in Nigeria has been estimated to comprise 1.6 million cattle, 13.5 million sheep, 26 million goats, approximately 2.2 million pigs and 150 million poultry.
Although emissions through the burning of fossil fuels have typically been regarded as one of the major contributors to GHG emissions, FAO (2006) reports the substantial emissions from the farm animal production sector, contributing approximately 18%, or nearly one-fifth of human induced GHG emissions, is a major threat to the environment. Other nitrous oxide emissions are generated from agricultural soils, fertilizer application and agrochemicals. Recently, the use of fertilizer has increased following the introduction of E-wallet, where farmers receive fertilizers and agrochemicals directly from the government.
Emissions from CH 4 and N 2 O are primarily from agriculture making the agricultural sector the largest producer of non-CO 2 emissions. Emissions of N 2 O (even in a small quantity) cause significant radiative force due to their global warming potential. Increased soil temperatures coupled with high moisture conditions during cooler months will increase N 2 O production in the soil (Ma et al., 2007). However, the need for immediate and far reaching changes in current animal agriculture practices and consumption patterns are both critical if GHGs from the farm animal sector are to be mitigated. Table 6a and b presents percentage CO 2 -eq emissions in line with the IPCC emission sector description obtained by multiplying the emissions by the gas global warming potential (GWP). The results revealed that the fugitive emissions from oil and gas accounted for the highest (75.27%) contribution to CO 2 -eq emissions, and was identified as the most polluting sector, known to pollute because of their technology (associated with the discovery of more non-associated gas (NAG) reserves in deeper reservoirs, the development of deep offshore oil fields with huge associated gas (AG) reserves, participation in the gas export business through the Nigerian Liquefied Natural Gas (NLNG) Company, and increasing demand for local gas supply for power generation). This is as a result of increased gas flaring employed to dispose off associated gas in major petroleum/oil producing areas in the country.
Records has it that there were 39 companies directly involved in oil and gas production in Nigeria, producing natural gas from 189 fields with daily AG production of 4.74 bscf/d and NAG production of nearly 3.46 bscf/d in 2015. Ajugwo (2013), in his study reported that Nigeria flares about 17.2 billion m 3 of natural gas per year in conjunction with the exploration of crude oil in the Niger Delta. This high level of gas flaring is equal to approximately one quarter of the current power consumption of the African continent.
From an economic perspective, the main interest of Nigerian government in the oil industry is to maximize its monetary profits from oil production. Oil companies find it more economically expedient to flare the natural gas and pay the insignificant fine than to re-inject the gas back into the oil wells. Additionally, because there is an insufficient energy market especially in rural areas, oil companies do not see an economic incentive to collect the gas.
However, these massive oil exploration and exploitation processes has not only created environmental, health, and social problems in local communities near oil producing fields, but has also resulted in an increased emission which causes climate change. This suggests the need for government to enforce the elimination of routine gas flaring by 2020, with unavoidable gas flaring limited to 2% of total gas production. Similarly, the remaining sectors were identified as important sectors because of the weight they have on the economy.

POLICY IMPLICATIONS AND CONCLUSIONS
It can be concluded that the contributions of emission driven sectors based on the 2006 IPCC description to CO 2 -eq emissions in Nigeria cannot be over-emphasized. Improvement in techniques and practices is an important mitigation options for sectors that pollutes through its own production process. But for sectors that are regarded as 'important' because they make other sectors pollute, this option may only be effective when there is a reduction in the demand for intermediate products from direct polluters like fugitive emissions from oil and gas as it accounted for the highest contribution of percentage CO 2 -eq emissions when compared to other sectors. However, increases in methane and nitrous oxide emissions especially from the agricultural sector, suggests the need to lower stocking densities as well as inputs of concentrated feed in order to contribute to better energy balances in the agricultural sector.

RECOMMENDATIONS
Technological improvements and best practices would be an effective emission mitigation measure for sectors that pollutes through its own production process but for other sectors that are important because they make other sectors to pollute, these measures would only be effective if they reduce intermediate demand to directly polluting sectors.
The absence of good and adequate policy has an undesirable effect on the environment and therefore the quality of the agricultural sector. Hence, policies geared towards encouraging the planting/maintaining of efficacious plants, candlenuts as well as the broad leaves of banana plants; discouraging deforestation and soil erosion due to over cropping would not only minimize environmental degradation but will also mitigate emissions in the agricultural sector.
Creation of awareness on the need to practice organic farming (since it has the potential to use less energy) will not only prohibit the use of synthetic fertilizers and pesticide that leads to increased emissions, but will also improve energy efficiency in the agricultural sector.
There is need to adopt the use of compost, as it not only offers environmental and societal benefits towards the mitigation of CO 2 -  eq emissions directly and indirectly through carbon sequestration in soil and substitution of nitrogenous and other synthetic fertilizers, but also helps in enhancing long term agricultural productivity and production.
The result of the study also revealed increases in methane and nitrous oxide emissions especially from animal manure, thus, suggests the need for government to support waste management in all the states in Nigeria to have a sequel structure to safe disposal of organic matter from cattle. Also, there is need to lower stocking densities as well as inputs of concentrated feed in order to contribute to better energy balances in the agricultural sector.
Finally, the result of the study also reveals increases in emissions in the fugitive emissions from oil and gas, as well as the manufacturing, energy and construction industries by 2027. This suggests the need for the Nigerian government to ensure the security of fuel source for power generation by mandating oil companies to channel their flared gases to power plant. In addition, there is need for government, Federal Environmental Protection Agency (FEPA) as well as the Department of Petroleum Resources (DPR) to enforced environmental regulations, implement anti-flaring policies for natural gas waste from oil production, monitor the emissions and ensure effective compliance by the citizenry.