Methane emissions and their climate effects have been given an increasing amount of attention over the last few years from academia, industry and policy makers. The US Environmental Protection Agency (EPA) have lead the way in proposing new performance standards to reduce methane emissions from the natural gas industry by 40% by 2025 from 2005 levels.
But how much of a climate problem really is methane emissions from gas? There are two main issues: methane emissions are highly variable across different regions and processes; and the climate changing effect of methane changes a lot over time. Here, we delve into these two issues in order to provide some clarity, based on recent research carried out at the Sustainable Gas Institute at Imperial College London.
Variable methane emissions: Analysing data from over 250 emissions studies, the range of emissions is extremely large all across the natural gas supply chain, everywhere from identifying and drilling the well, processing the gas to delivery to the end-user. Whilst some emissions are extremely large, the vast majority of estimates are at the lowest end of the scale, suggesting that only a small number of ‘super emitters’ are skewing the distribution of emissions. These super emitting facilities or equipment are at every stage of the supply chain and contribute the majority of emissions.
The vast majority of these emissions are avoidable. Key emission sources were typically from unconventional well completions, liquids unloading, compressors and gas-driven pneumatics. For all of these processes and equipment, emissions are largely dependent on the technologies used for the operation, as well as the operational and maintenance practices.
How potent is methane as a greenhouse gas?: The vast majority of emissions studies assume that methane is 25 - 34 times more potent than carbon dioxide (CO2) as a greenhouse gas. This is known as the global warming potential (GWP) and allows us to compare different greenhouse gases. While it is a very useful unit for policymakers, it is not very accurate. This is because the potency of methane actually changes considerably over time: it is extremely potent in the short term (approximately 120 times stronger than CO2) but only lasts in the atmosphere for around 12 years, as opposed to CO2 which lasts for thousands of years. This means that using a single GWP figure ignores this change over time.
The standard convention is to use the average effect over 100 years, which is 34 g CO2/ g methane. However, choosing this timeframe is arbitrary and some studies have used a 20 year time frame, for example. The use of a single GWP figure as the climate metric is being questioned more and more by experts, and other climate metrics have been proposed as replacements but it is still the standard convention. The choice of metric and timeframe is the subject of work currently being carried out by the Sustainable Gas Institute.
How much of a climate problem is methane emissions from natural gas?: The high variation in emissions and the uncertainty around global warming potentials has caused much confusion in trying to understand the relative benefits, or otherwise, of using gas for heat or electricity generation. What is clear, however, is that a small emission of methane can have a large climate impact in the short term. So, as we move towards decarbonising our global energy systems and stabilising our climate, methane emissions will begin to have a greater impact. Studies have indicated that reducing methane emissions now will significantly decrease the peak global temperatures which is vital for minimising the societal impact of climate change.
It is also clear that we know which technological, operational and maintenance practises will help us to minimise these emissions and while industrial methane emissions have been reduced, much more could be done. Download the Sustainable Gas Institute’s white paper, to know more about methane and CO2 emissions from the natural gas supply chain.
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Photo: Courtesy of Imperial College London
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