A Qualitative Assessment of the Trends, Distribution and Sources of Methane in South Africa

Abstract

Methane (CH₄) is the second most important greenhouse gas (GHG) in terms of its concentration and impact on the climate. In the present study, we investigate the trends, sources and distribution of CH4 in South Africa. The study uses satellite datasets from Sentinel-5P and the Atmospheric Infrared Sounder (AIRS). The study also uses credible datasets from the World Bank, Statistics South Africa and the Global Methane Initiative (GMI). The results show an increasing trend of CH₄ from 1970–1989. A turning point is observed in 1989, where a decreasing trend is observed from 1989–2001. An increasing trend is then observed from 2001 to 2021. A high concentration of CH₄ is observed in the northern and interior parts of South Africa. The results also show that CH₄ concentration is influenced by seasonal variations. The September–October–November (SON) season has the highest CH₄ concentration distribution in South Africa. The World Bank, Statistics South Africa and the GMI CH₄ indictors show that agricultural activities, i.e., involving livestock, are the greatest emitters of CH₄ in South Africa, followed by landfill sites. From the livestock data, sheep are the highest emitters of CH₄. The increasing CH₄ trend is a concern and efforts need to be made to drastically reduce emissions, if South Africa is to meet the 1997 Kyoto Protocol, 2015 Paris Agreement, sustainable development goal 13 (SDG 13) and the COP26 outcome agreements.

1. Introduction

Greenhouse gases (GHGs) absorb and emit radiant energy within the thermal infrared range, causing the greenhouse effect. The main gases responsible for the greenhouse effect are carbon dioxide (CO₂), nitrous oxide (N₂O), water vapor and methane (CH₄). An increase in the atmospheric concentrations of GHG produces a positive climate forcing. CH₄ is the second most important greenhouse gas in terms of its concentration and impact on the climate [1,2]. In 2019, global CH₄ was estimated at around 570 million tons (Mt) [3]. It was found that about 60% of global CH₄ was influenced by anthropogenic sources (i.e., landfill, oil and natural gas systems, agricultural activities, coal mining, and wastewater treatment), and 40% was influenced by natural sources (i.e., wetlands, volcanoes, ocean sediments and wildfires) [4,5,6,7,8]. In addition to the climate impact, high levels of CH₄ have an impact on human health. In fact, high levels of methane can reduce the amount of oxygen breathed from the air, which can change the breathing and heart rate conditions that might lead to death.

Livestock is agriculture’s largest CH₄ contributor by 98% [2]. On the other hand, wetlands are the world’s largest natural sources for methane, accounting for 20–40% of global methane emissions [5,6,7]. Parker et al. [6] revealed that CH₄ trends have shown no growth, but rather a decline between the 1980s and 2000s, and this is due to the balance between different sources and sinks. In contrast, an abrupt increase in atmospheric CH₄ occurred between 2007 and 2014 [5,6,7,9,10]. This increase was caused by the prominence of wetlands, production of fossil fuel, and livestock [6]. Africa is occupied by 4.7% of wetlands, while South Africa is occupied by 2.4% [11]. African wetlands are confirmed to be the largest global contributors of CH₄ emissions [4,8]. Moreover, CH₄ content has been declared to be significant in developing countries due to inadequate manure management and feed production [1]. Forabosco et al. [1] estimated that it is most probable for animals to increase globally to approximately 34 billion by 2050. When that occurs, an improved feed production and manure management is required. Another concerning factor is rapid population growth and development activities, which may see a potential increase in the CH₄ emission level [12].

South Africa is not exempt from the rise in CH₄ emission levels, in fact, the largest quantity of CH₄ was detected in the Eastern Cape province of South Africa in 2010, as a result of the rapid increase in the number of cattle [2]. Furthermore, CH₄ in the Gauteng province was also declared as high, due to feedlot emissions [2]. Therefore, this study intends to focus on the CH₄ trends in South Africa from 1970 to 2021 using several data sources, including the World Bank indicators, Statistics South Africa (Stas SA) indicators and satellite data. This study is of paramount significance not only because CH₄ is the second most important GHG, but also because CH₄ traps heat 28 times more than CO₂, thus increasing global warming [2,4,5,6,8,13]. Additionally, CH₄ has a much shorter atmospheric lifetime than CO₂ [1,2,8], but can trap heat more effectively. If the world aspires to meet the sustainable development goal 13 (SDG 13), the 2015 Paris Agreement, and the 1997 Kyoto Protocol, then CH₄ needs to be managed by advocating for rigorous CH₄ reduction.

2. Methane Sources and Sinks

CH₄ emissions can be broadly grouped into three categories: (1) biogenic, (2) pyrogenic and (3) thermogenic [14]. Biogenic emissions are produced and released from living organisms, such as plants and animals. Pyrogenic emissions are produced by the incomplete combustion of biomass and soil carbon during wildfires. Thermogenic emissions, on the other hand, are formed over millions of years through geological processes. CH₄ is emitted from the subsurface into the atmosphere through natural features (such as terrestrial seeps, marine seeps and mud volcanoes), and through the exploitation of fossil fuels, such as coal, oil and natural gas [14]. Figure 1 shows some major sources of CH₄ emissions. Livestock, such as cattle, sheep, and goats, emit the largest quantity of CH₄ gas because they are ruminants [15,16,17]. Ruminants have microorganisms in their stomachs called methanogens, which produce CH₄ through methanogenesis [16,18]. Hook et al. [16] showed that ruminants emit about 86 million tons (Tg) of atmospheric CH₄ annually, making ruminants account for 30% of the CH₄ emitted into the atmosphere daily [15]. Another major source of CH₄ is landfills and open dumps. The decomposition of municipal solid waste (MSW) in developed countries usually ends up in landfills, which emit CH₄ gas during the decomposing stages [19,20,21]. However, in developing countries, open dumps are still being used as the final disposal method for solid waste [22]. Another major source of CH₄ is oil and gas extraction and production activities. The main activities that produce CH₄ occur during upstream production, which include venting, incomplete combustion during flaring and fugitive emissions [23].

The major sinks of CH₄ are shown in Figure 1. The troposphere is the largest sink for CH₄. CH₄ in the troposphere reacts with hydroxyl (OH) radicals, forming mainly water and CO₂. Other CH₄ sinks include methanotrophic bacteria in soils, oxidation by chlorine radicals in the marine boundary layer, and photochemical destruction in the stratosphere [24].

There are a variety of possible methods to balance sources and sinks of CH₄ to produce what is termed “net zero emissions”. The two most suggested approaches are, firstly, to gradually reduce global anthropogenic CH₄ emissions towards zero. It is anticipated that slowing down the emission rate of CH₄ increases the rate of CH₄ uptake by natural sinks. Secondly, develop methods (which are still undeveloped) to remove large concentrations of CH₄ gas from the atmosphere. This method requires a thorough understanding of atmospheric chemistry and atmospheric science engineering. It must be noted that there some uncertainties still exist in the identification and quantification of individual sources and sinks. Most importantly, there is much that is still unknown about CH₄ sources and sinks and their evolution over time [25].

3. Data and Methods

3.1. Sentinel-5P (TROPOMI)

The TROPOspheric Monitoring Instrument (TROPOMI) is an instrument on board the Copernicus Sentinel-5 Precursor (5P) satellite. Sentinel-5P was launched on 13 October 2017 with a mission to perform atmospheric measurements with a high spatio-temporal resolution to be used for air quality, ozone and UV radiation, and climate monitoring and forecasting. It consists of a high-resolution spectrometer system operating in the ultraviolet-to-shortwave infrared range with 7 different spectral bands: UV-1 (270–300 nm), UV-2 (300–370 nm), VIS (370–500 nm), NIR-1 (685–710 nm), NIR-2 (745–773 nm), SWIR-1 (1590–1675 nm) and SWIR-3 (2305–2385 nm). TROPOMI, on board Sentinel-5p, maps the global atmosphere daily with a resolution of 7 km × 3.5 km (which is 13 times better than the Ozone Monitoring Instrument (OMI)) [26]. This allows for the resolution of fine details to be obtained, including the detection of much smaller methane (CH₄) plumes. Other main TROPOMI data products include carbon monoxide (CO), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), formaldehyde (HCHO) and aerosols. More details on Sentinel-5P can be found in Theys et al. [26], Tilstra et al. [27] and Verhoelst et al. [28]. In this study, the CH₄ product was used. The processing of CH₄ TROPOMI data was carried out in the Google Earth Engine (GEE), which is a cloud-based platform that enables the large-scale processing of satellite data. TROPOMI uses absorption information from the Oxygen A Band (760 nm) and the SWIR spectral range to monitor CH₄ abundances in the Earth’s atmosphere. Uncertainties for XCH₄ are only based on the single sounding precision due to the measurement noise. The current data release only provides XCH₄ over land. In the Level 2 processing of the data, clouds are removed; hence, in the GEE platform, no filters were used. TROPOMI has a measurement frequency of one day. A total of 1277 days of observation, from 1 July 2018 to 31 December 2021, was used.

3.2. AIRS

The Atmospheric Infrared Sounder (AIRS) was launched on the Earth Observing System (EOS) aqua satellite in May 2002. The AIRS instrument was designed to provide continuous global observations with an accuracy equal to that of radiosondes [29]. Most importantly, AIRS was developed to address (1) the global water and energy cycle, (2) climate weather connection, (3) atmospheric composition and (4) weather prediction [29]. AIRS is an infrared grating spectrometer that operates in the thermal infrared portion of the spectrum, from 3.7 µm to 15.4 µm. It has 2378 channels covering about 314 in this range, with a spectral resolution (λ/Δλ) of about 1200. AIRS has a frequency of one day. More details on AIRS can be found in Lambrigtsen et al. [29] and Morse et al. [30]. The AIRS data is obtained from the Giovanni platform (https://giovanni.gsfc.nasa.gov/giovanni/ (accessed on 10 January 2022)) and the data is Level 2 processed and is cloud free, so no filters were used.

3.3. Statistics South Africa (Stats SA) Indicators

Stats SA is the national statistical service for South Africa, which produces timely, accurate and official statistics (http://www.statssa.gov.za/ (accessed on 10 January 2022)). In this study, Stats SA data was used to retrieve the livestock data from the years 1996 to 2020. The livestock data included the number of cattle, sheep and goats in South Africa per year. Pigs’ CH₄ emission data were omitted as it has been shown that pigs emit far less CH₄ compared to cattle, sheep and goats [2].

3.4. World Bank Indicators

World Development Indicators (WDIs) is the primary World Bank collection of development indicators, compiled from officially recognized international sources (https://databank.worldbank.org/home.aspx (accessed on 10 January 2022)). It presents the most current and accurate global development data available, and includes national, regional and global estimates. The World Bank data is accurate and reliable, however, developing countries still face a number of problems in providing statistics that meet these criteria. South Africa, as a developing country, has managed to produce resources that enable them to produce quality-controlled data. More on the quality of the World Bank data can be accessed via (https://datahelpdesk.worldbank.org/knowledgebase/articles/906534-data-quality-and-effectiveness (accessed on 10 January 2022)) In this study, the total CH₄ emission data over South Africa between the years 1970 to 2018 were used.

3.5. Global Methane Initiative

The Global Methane Initiative (GMI) is an international public–private initiative that advances cost-effective, near-term methane abatement and the recovery and use of methane as a clean energy source in three sectors: (1) biogas (including agriculture, municipal solid waste, and wastewater), (2) coal mines, and (3) oil and gas systems (https://www.globalmethane.org/ (accessed on 11 January 2022)). GMI was launched in 2004 with the aim of identifying and quantifying methane emission sources to reduce greenhouse gas (GHG) emissions, improve air quality, increase energy security and enhance economic growth. GMI has 46 partner countries and over 700 Project Network members with whom they exchange information and technical resources. GMI also uses data obtained from the U.S. Environmental Protection Agency (U.S. EPA) report (https://www.epa.gov/global-mitigation-non-co2-greenhouse-gases (accessed on 11 January 2022)). The EPA technical report provides a consistent and comprehensive set of historical and projected estimates of emissions and technical and economic mitigation estimates of non-CO₂ GHGs from anthropogenic sources for 195 countries. The analysis provides information that can be used to understand national contributions of GHG emissions, historical progress of the reductions, and mitigation opportunities. In this study, the CH₄ emission by type was used. Specifically, energy, landfill waste, water waste, livestock enteric emissions and livestock manure were analyzed.

3.6. Sequential Mann–Kendall (SQMK) Test

The Sequential Mann–Kendall (SQMK) test proposed by Sneyer [31] was used to identify the abrupt changes in significant trends [32,33]. This test sets up two series: a progressive $u\left(t\right)$ and a retrograde (backward) series $u^{\prime }\left(t\right)$. If they cross each other and diverge beyond the specific threshold value, then there is a statistically significant trend. The point at which they cross each other indicates the approximate year in which the trend begins [34]. The threshold values in this study are ±1.96 (p = 0.05), with the crossing point estimating the year in which the trend begins. The SQMK test has the following steps:

i

At each comparison, the number of cases x_i > x_j is counted and indicated by $n_i$, where x_i (i = 1,2,…n) and x_j (1,2,…n) are the sequential values in a series, respectively.

ii

The test statistic t_i is calculated by

$$t_i={\displaystyle \sum }_{j=1}^i{n}_j$$

(1)

iii

The mean E(t) and the variance var(t_i) of the test statistic are calculated by

$$E\left(t\right)=\frac{n\left(n-1\right)}{4}$$

(2)

$$\mathrm{var}(t_i)=\frac{i\left(i-1\right){(2i+5)}_{⬚}}{72}$$

(3)

iv

The sequential progressive value can be calculated as

$$u\left(t\right)=\frac{t_i-E\left(t\right)}{\sqrt{\mathrm{var}(t_i)}}$$

(4)

Similarly, the values of $u^{\prime }\left(t\right)$ are computed backward, starting from the end of the series. In this study, SQMK was performed on CH₄ emission data in South Africa. The CH₄ concentration data used were retrieved from AIRS.

4. Results and Discussion

4.1. Trends and Spatial Distribution of CH₄ in South Africa

Figure 2a shows a linear trend of CH₄ emissions in South Africa. An increase in CH₄ emissions is observed between the years 1970 and 1989. There are a number of likely factors that could have led to the gradual increase in CH₄ in the period from 1970–1989. Firstly, the increasing population growth meant an increase in electricity demand, food security (increase in agricultural activities) and waste management (landfill and dumping sites). The increase in energy demand means an increase in the production of electricity. South Africa is dominated by coal-fired power plants [35], therefore more coal mining activities would increase, thus releasing more CH₄. Food security leads to the production of more crops, plants and livestock. The increase in the livestock would add to the increase in CH₄ emissions, as it is known that livestock emit large quantities of CH₄. An increase in solid waste from the public would lead to an increase in landfill and dumping sites. The decomposition of the solid waste releases CH₄ into the atmosphere. All these factors combined can increase the CH₄ emission drastically over time. However, between 1989 and 2001, a gradual decrease in CH₄ emissions can be observed. The decrease could be attributed to the improvements to waste management in landfills and open dumping sites. Furthermore, CH₄ reducing feed additives and supplements inhibiting methanogens in the rumen could have been used to reduce enteric CH₄ emissions. After the year 2000, an increase in CH₄ emissions was observed yet again.

The AIRS instrument, from 2002 to 2021, also showed an increasing trend of CH₄ concentration (see Figure 2b). Overall, the SQMK trend in Figure 2b shows that the CH4 concentration increased year on year. Shikwambana et al. [36] showed that the economy of any country is linked to the emission regime. The more the economy grows, measured by the gross domestic product (GDP), the more emissions there are, if non-clean technologies are used. However, in South Africa, the economy grew substantially in the 2000s. This resulted in more investments in the country and more people coming in to set up various companies. This again resulted in more demand for food security, energy and waste disposal sites. With no strict measures for emissions, industries and emerging farmers did not take heed of the CH₄ emissions, as they were not publicized as CO₂ emissions. Only recently, in the last twenty years, has enough noise been generated about the global warming dangers of CH₄. New spaceborne instruments as well as ground-based instruments were developed to actively measure CH₄ emission hotspots. TROPOMI and AIRS are good examples of recent satellite technologies that were developed to measure CH₄ concentrations at mid-to-high resolutions. The sudden rise in CH₄ emissions in the 2000s was a global phenomenon, which is still not understood, and efforts are being made to establish the trend. There was a hypothesis that stated that a decline in OH contributed to the rise in CH₄ concentrations [24]. However, in this work, we further speculate on the possible CH₄ emission increase scenarios over time in South Africa.

The mean spatial distribution of CH₄ concentrations in South Africa for the period from 2018–2021 is shown in Figure 2c. High concentrations of CH₄, 1826–1850 ppbV, are observed in the interior and northern parts of South Africa. The Northern Cape (NC), North-West (NW), Mpumalanga (MP), Gauteng (GP), Free State (FS) and Limpopo (LP) provinces have areas with high concentrations of CH₄. The high concentration of CH₄ in NC, NW, LP and FS can be attributed to livestock farming. Mining activities emitting CH₄ can also be observed in NC, LP and MP. The Ephemeral Wetlands in NC also contribute to CH₄ concentrations. Energy-emitting activities can be found in MP and GP. GP is one of the most densely populated provinces in South Africa. This large population of people results in various landfill and dumping sites across the province. Therefore, solid waste disposal sites greatly contribute to the emission of CH₄ in this region. Overall, the observed CH₄ concentration distribution in South Africa results from various sources. However, agriculture, landfill, energy production and wetlands are the main drivers of CH₄ emissions across the country.

A year-on-year trend for the spatial distribution of CH₄ concentration in South Africa is shown in Figure 3. Data for the year 2018 was available from June; this is why there are white gaps in Figure 3a. The white gaps mean that no data is available. However, the figure still shows some dominance of CH₄ concentration in the NC, NW and LP provinces. Although CH₄ was not prevalent in 2018, the figure shows the emergence of CH₄ in these regions. In 2019, as can be observed in Figure 3b, the presence of CH₄ is starting to be dominant in the NC province. The emergence of CH₄ can also be noticed in the GP and MP provinces. By the year 2020 (see Figure 3c), the interior and northern parts of South Africa have a high CH₄ concentration. The year 2021 (see Figure 3d) shows an even more horrifying picture of CH₄ concentrations dominating most of South Africa. This is of serious concern and needs to be addressed at a policy-maker level. Unless drastic actions are taken to mitigate this issue, the trend suggests that CH₄ concentrations may continue to increase year-on-year. The continuous increase in CH₄ concentrations is caused by the continuous emissions of CH₄ from various sectors, such as agriculture, energy, waste management and natural sources, such as wetlands. The consequences of such a significant rise in CH₄ concentrations is a rapid rise in the regional temperature, which may lead to a reginal global warming scenario and climate change.

4.2. Averaged Seasonal Spatial Distribution of CH₄ over South Africa

Sweeney et al. [37] stated that CH₄ emissions are sensitive to temperature, thus CH₄ concentrations vary seasonally. Dangal et al. [38] showed that the rise in CH₄ concentrations in China and Mongolia from May to September was due to rising temperatures. Furthermore, Akimoto et al. [39], Ganesan et al. [40] and Tian et al. [41] also showed the seasonal variation of CH₄ concentrations. They attributed these changes to rice cultivation, wetlands, microbial activity and burning biomass, to name a few. Figure 4 shows the seasonal distribution of CH₄ concentrations in South Africa. The largest distribution of CH₄ concentrations is observed during the September–October–November (SON) season (see Figure 4d), while the least CH₄ concentration distribution is observed during the December–January–February (DJF) season (see Figure 4a). The majority of South Africa, except the southwestern regions, experience rainfall in the SON season. South Africa also experiences moderate temperatures ~23 °C. Unlike some studies in which temperature drives the seasonal variation of CH₄ concentration, these results show that water availability in terms of the precipitation–evaporation ratio can also play a more vital role than temperature [42]. Therefore, the large CH₄ concentration in the SON season can be attributed to an increase in rainfall, which likely increases the wetlands, and thereby increases CH₄ released from wetlands. Furthermore, biomass burning that occurs in the late-June–July–August (JJA) season and the SON season [43] also contributes to the total CH₄ concentration. On the contrary, both DJF and the March–April–May (MAM) seasons (see Figure 4a,b) show relatively lower CH₄ concentrations (1784 ppbV and 1805 ppbV), except for the NC province. A higher CH₄ uptake system (sinks) could exist in these seasons, compared to the other seasons. Firstly, well-aerated soils, such as in forests, grasslands and arable lands, are considered as the sink of atmospheric CH₄ [44]. This process could slightly contribute to the sink process during these seasons. Secondly, speculation with very little certainty suggests that OH is more dominant during these seasons, and thus removes some CH₄ from the atmosphere. Globally, the OH-related uncertainties in the CH₄ budget still remain. This is because OH has a relatively short lifespan; therefore, it is difficult to gather global OH concentrations using direct observations.

4.3. Sources of CH₄ in South Africa

Figure 5 shows the total contribution and linear trends of CH₄ emissions by category and livestock. It is important to identify the main contributor of CH₄ emissions as this helps in the mitigation stages. The trend obviously assists in determining whether there is an increase, decrease or no change in the emission regime. Depending on the outcome, necessary measures by policy makers need to be taken to mitigate the situation. Figure 5a shows that agricultural activities, i.e., livestock farming, are the greatest source of CH₄ emissions in South Africa. Specifically, livestock enteric emissions are the greatest contributor, with 52% of the total emissions. Du Toit et al. [2] showed that the CH₄ emission from livestock is dependent on the dry matter intake. Landfill sites, on the other hand, are the next biggest emitter producing 40% of the total CH₄ emissions in South Africa. Waste disposed into landfill sites undergoes aerobic decomposition, which produces a small amount of CH₄. Thereafter, the anaerobic condition prevails, and due to methanogen activities, the waste emits CH₄ for years, even if the landfill site is closed [45]. Livestock manure contributes 5% of the total CH₄ emissions, while energy production and wastewater each contribute 2% of the total CH₄ emission. The linear trend in Figure 5b shows no change in the trend of CH₄ emissions in the livestock enteric emissions, livestock manure, wastewater and energy source. These sources do not show any major changes in the emission regime from 1990 to 2020. The landfill waste, however, showed a decreasing trend in CH₄ emissions from 1995 to 2000. This trend is observed in Figure 2a as well. It is anticipated that the decrease might have been caused by stronger CH₄ sinks during that period. However, from 2001 to 2020, a steady increase in CH₄ emissions can be observed. This increase implies that the emission sources are greater than the CH₄ sinks. Again, this trend follows the global increasing trend of CH₄. There are still, however, uncertainties of the cause of the increasing CH₄ concentrations year-on-year.

From the agricultural activities, livestock is further categorized as the highest CH₄ emitter. Figure 5c shows that sheep are the highest emitters of CH₄ compared to the other livestock. Cattle are the second highest livestock emitters, followed by goats, which are the third highest emitters of CH₄. To make the issue even more complex, Figure 5d shows that there are more sheep than cattle and goats. Depending on the rate of emission from sheep, this implies that sheep could have a higher CH₄ emission. On the brighter side, the number of sheep trend shows a steady decreasing number of sheep from 1996 to 2020. The number of sheep decreased from ~2.89 × 10⁷ in 1996 to ~2.16 × 10⁷ in 2020, a decrease of ~25.3 %. The cattle and goat trend shows no changes in their numbers from 1996 to 2020. The number of cattle remained at ~1.33 × 10⁷ and the number of goats remained at ~6.4 × 10⁶.

The current issue is to reduce the CH₄ emissions from livestock. Breeding less livestock might solve the emission problem, but this might cause food security problems. One solution would be to use feed additives that can inhibit the microorganisms that produce CH₄ in the rumen, which can then reduce CH₄ emissions.

5. Overall Remarks to CH₄ over South Africa

Although some of the CH₄ sources in South Africa might not be quantified, South Africa has many sources of CH₄. One of the emitters is coal mines. South Africa is heavily dependent on coal for energy production, which means there are lots of coal mines that supply the power stations. Underground coal mines account for most CH₄ emissions. There are three ways CH₄ can be released from mining activities: (1) by degasification systems, (2) by ventilation systems and (3) by abandoned mines. South Africa has ~19 active coal mines. According to Stats SA, coal production amounted for 306 million metric tons in 2019. Another important source of CH₄ is landfill or waste sites. Waste sites in South Africa were estimated at 1085 in 2015; this was up from 42 in 2008. The rate of new waste sites, especially in metropolitan cities, is alarming. The new sites are a result of rural–urban migration. Migrants from the poor rural settings occupy land at the boundaries of the city and set up informal dwelling households. Their aim is to be near the city and look for employment. However, during their stay, they accumulate waste that needs to be disposed. They then set up informal dumping sites in which all the waste is disposed. The decomposing waste releases all sorts of chemicals, which, firstly, creates a health problem for the community and, secondly, releases CH₄ into the atmosphere. Most of the dumping sites are established in this way. The most globally discussed CH₄ source, including South Africa, is the emissions from livestock. The results presented in Section 4 show that livestock has a vast impact on the concentration of CH₄. Therefore, significant efforts need to be made to reduce the amount of CH₄ emitted by these animals. One of the proposed methods is to change the feed intake of livestock. Feed the animals with food that emits less CH₄, e.g., adding fat to the diet of cows and reducing methanogens or other microbes involved in methanogenesis.

More work needs to be conducted to understand the sources and sinks of CH₄ in South Africa. This knowledge helps to assess the levels of CH₄ concentrations and what mitigation and adaptation strategies need to be implanted to reduce and/or obtain to ‘non-zero’ emissions of CH₄. The creation and/or enhancement of artificial and natural CH₄ sinks need to be rapidly implemented. CH₄ is a harmful gas that needs our immediate attention.

6. Conclusions

The study shows an increasing trend of CH₄ concentrations in South Africa. This trend is observed globally, but the exact reasons for the increase are still unclear. However, this study attempts to suggests some possible CH₄ sources and activities responsible for the increase in CH₄ emissions in South Africa between the years 2000 and 2021. The decrease in CH₄ sinks is one factor that results in an increase in CH₄ concentration. The other factor is the high emission of CH₄ from the agricultural sector and the waste management sectors. Population growth and migration into the cities are the key drivers for the increase. CH₄ emissions show some seasonal variations, with the SON season showing the highest CH₄ concentration distribution. The rainy conditions are attributed to the high concentration of CH₄. The World Bank, Stats SA indicators and the GMI data were crucial in showing the contribution of the total methane sources by category and livestock in South Africa. Overall, the study presents a high-level view of the trends and distribution of CH₄ in South Africa. The study is good enough for policy makers in the country to understand the scenario of CH₄ emissions and make informed decisions. This paper presents a high-level perspective on the distribution and trends of CH₄ in South Africa. A detailed quantitative study needs to be carried out to understand the amounts of CH₄ released from the hotspots in South Africa. This will then lead to a plan of action to introduce various strategies to reduce the amount of CH₄ emissions.

One of the gaps in this study is the lack of CH₄ emission data. More CH₄ monitoring stations should be setup to fully understand the sources and trends of CH₄ emissions at a local level. Furthermore, a follow-up study should investigate the relationship between CH₄ emissions and concentrations with meteorological and vegetation parameters, such as temperature, precipitation, radiation forcing and the Normalized Difference Vegetation Index (NDVI). This study contributes to the understanding of the CH₄ emission increase or decrease over time.