Methane releases from natural gas are a key factor in creating parity between the overall GHG emissions from gas and coal
Crude oil (from which natural gas is made) in a beaker, alongside black hard coal lumps. Photo for representation. Courtesy: iStock Natural gas has been called a ‘bridge fuel’ for countries looking to transition away from coal and oil dependency, and as they pursue a pathway towards renewables and electrification. Hailed as a cleaner energy source than other fossil fuels, especially coal, natural gas has a lesser climate impact than coal because it emits 50 per cent less CO2 into the atmosphere.
The Intergovernmental Panel on Climate Change has emphasised a greater urgency in phasing out coal over reducing gas usage for the 1.5°C pathway, which places a heavy burden on coal-dependent Global South countries. At COP26, the United Kingdom government focused on tackling “cash, coal, cars, and trees”, disregarding the fact that wealthy Global North countries are the biggest historical emitters owing to coal-fuelled industrialisation, and developed countries continue to overuse oil and gas despite exhausting their share of the carbon budget. At COP28 in Dubai last year, the United Nations Framework Convention on Climate Change mentioned “transitional fuels” for energy security in its outcome of the First Global Stocktake, alluding to natural gas. Amidst global energy politics, this narrative of natural gas being ‘cleaner’ in comparison to coal warrants closer scrutiny.
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From a climate standpoint, coal and gas are compared by assessing their life cycle greenhouse gas (GHG) emissions. A “lifecycle assessment” evaluates all the emissions throughout the coal and gas supply chains from extraction, processing, and transportation to end use. Comparisons based only on end-use combustion might be limited in their purview and paint an incomplete picture of the total GHG emissions. Data shows that a given coal-fired power plant in Europe emits GHG emissions of 970 tonnes of carbon dioxide equivalent (CO2e) per gigawatt-hour of electricity over its lifecycle. In comparison, a given oil-fired power plant emits 720 tonnes and a given gas-fired power plant emits 440 tonnes of CO2e per gigawatt-hour of electricity, over their respective lifecycles.
Even so, there are differing perspectives on whether natural gas truly is ‘cleaner’ for the climate than coal. When comparing coal to gas, it is important to factor in methane emissions alongside CO2 emissions. The primary component of natural gas is methane, comprising 70-90 per cent of its composition. Methane is the second-most abundant GHG after CO2. Although methane dissipates faster than CO2 in the atmosphere, it has a much stronger planetary warming effect. While possessing a short atmospheric lifetime (12-15 years, compared to 150-200 years of CO2), methane has a high global warming potential (GWP) which is 28 times that of CO2 over 100 years. GWP is a climate metric used to measure how much heat a GHG traps in the atmosphere relative to CO2. Over a 20-year period, methane traps over 82.5 times more heat than CO2.
Comparisons between pollutants such as CO2 (primary component of coal) and methane (primary component of gas) should be based on suitable climate projections. Methane has a strong near-term warming effect, unlike the long-term potency of CO2. Traditional climate models measuring the effects of methane over 100 years could end up overlooking its immediate heat-trapping potential, possibly skewing policy conclusions of natural gas versus coal emissions.
According to the Rocky Mountain Institute, methane releases from the natural gas supply chain are a key factor in equalising overall GHG emissions between gas and coal, creating emissions parity. Two kinds of methane releases from gas take place.
Methane leaks result in fugitive emissions, with varying estimates depending upon measurement methods: bottom-up (at the source) or top-down (from a height to capture area-wide emissions). A study published last year in the journal Environmental Research Letters found that as little as 0.2 per cent leakage rate of gas can be worse for the climate than coal in terms of net GHG emissions. The global average natural gas leak rate is said to be between 2 per cent and 3 per cent. Methane plumes have also increasingly been detected by satellites and sensors.
The Clean Air Task Force (CATF), in a recent white paper, analysed the lifecycle GHG emissions associated with exported liquefied natural gas (LNG) and exported coal used for electric power generation. Both stack emissions and upstream emissions are considered when comparing the lifecycle emissions of coal and natural gas. Upstream emissions are emitted during production, processing, and transport of gas or coal. Downstream emissions are emitted during combustion of gas or coal. CATF’s analysis of LNG shipments exported from the US to Vietnam and coal exported from Australia to Vietnam shows that upon usage of these fuels in the country, a gas-fired power plant emits less CO2 (58 per cent less) from its stack than a coal-fired power plant. But the relative advantage of gas over coal diminishes and is about 24 per cent when full lifecycle emissions are considered. Deep decarbonisation through utilising natural gas for power generation hinges on mitigation of upstream and downstream CO2 and CH4 emissions.
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An upcoming study from Cornell University, pending peer review, finds that previous research has not accounted for CO2 emissions from gas liquefaction — a process in which gas is chilled to extremely low temperatures to convert it into a liquid state — and transport of LNG. The GHG footprint of LNG exceeds that of domestically consumed natural gas and even coal due to energy-intensive liquefaction and transportation processes, with GHG emissions ranging from 44 per cent to over double that of domestically produced coal for the average cruise (travel) distance of an LNG tanker.
Moreover, methane emissions from the oil and gas sector are said to be vastly underreported. As per a study, during 2010-2019, methane emissions from US oil and gas fields were 70 per cent higher than the US Environmental Protection Agency (EPA) inventory, revealing flaws in the EPA’s data-collection methods.
For emissions abatement, the International Energy Agency notes that oil and gas industry emissions can be cost-effectively mitigated through “ready-to-implement” measures which include tackling methane emissions, eliminating all non-emergency flaring, electrifying upstream facilities with low-emissions electricity, among others. Correspondingly, a report by Climate Policy Initiative highlights that the fossil fuel sector, particularly oil and gas, holds the highest methane abatement potential (34 metric tonnes of CH4 per year) through cost-effective measures, yet it receives less than 1 per cent of tracked methane abatement finance.
In the pursuit of cleaner energy, evaluating the true climate impacts of natural gas and coal remains crucial for informed decision-making in the transition away from fossil fuels.
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