A new study found that as little of a leakage rate as 0.2 percent of methane gas can make this fuel as dangerous for the climate as coal. Lisa Tostado takes a closer look at these findings.

For a long time, the gas industry made people believe that gas is a cleaner alternative to coal and an important “bridge fuel” in the fight to slow global warming. However, while indeed emitting less CO₂ during combustion, fossil gas is almost exclusively composed of methane. While methane stays in the atmosphere for a shorter period than CO₂, its global warming potential is 87 times stronger within the 20 years – timeframe we should consider in a world dangerously close to the Paris target already and committed to be climate neutral in three decades. That means: leaking from drill sites, processing plants and pipelines significantly reduce, or as we will see, even nullify the alleged climate benefits of fossil gas over coal.

There is now overwhelming evidence that fossil gas is leaking in far larger quantities than previously thought – and it does so along its entire supply chain. Sensors, infrared cameras and increasingly powerful satellites have been helpful in detecting methane emissions that are per se odorless and invisible. Most recently, in August 2023, the Clean Air Task Force published alarming findings about methane leaks in Australia’s fossil gas infrastructure on 80 different sites. Another example: A 2020 study by the Environmental Defense Fund found that 3.7% of fossil gas produced in the Permian Basin leaked into the atmosphere.

As the leakage rate is such a crucial factor to determine whether investments in gas rather than coal can even have a climate benefit, numerous studies have already looked at this issue so far. They found that if 2% to 5% of gas leaks into the atmosphere, gas-fired power plants were on par with coal plants in terms of the overall climate impact over a 20 year timeframe. These were the numbers I regularly cited which is why I was bewildered to now see a number as low as 0.2% in a new peer-reviewed study accepted last month in Environmental Research Letters.

The researchers from inter alia Harvard and Duke Universities as well as NASA advanced the science by considering the entire life cycle emissions of various greenhouse gasses of gas and coal (coal mines leak methane, too); and they did so for various use cases whereas previous studies focused on the power sector.

Interestingly, they also took into account sulfur dioxide (SO₂) released when burning coal. When this gas is emitted, it forms sulfate aerosols in the atmosphere which in turn reflect incoming sunlight back to space and therefore have a short-term cooling effect. As relatively positive as this may sound at first sight, sulfur dioxide does cause significant damage to human health via air pollution^[1]. The higher the coal sulfur content, the greater the capacity of SO₂ to mask coal mine methane leakage when evaluating the global warming potential, and the more critical scrubber efficiency^[2] is to protect public health.

When considering SO₂ aerosol emissions from coal, they find that global gas systems that leak over 1% of their methane when considering a 20 year timeframe have life-cycle emissions intensities that are on par with coal leaking methane at the IPCC emissions rate^[3]. Over the 20 year timeframe, two of their scenarios (low scrubber efficiency and low coal mine methane leaking) find that coal and gas are on par at 0.2% methane leakage from gas or lower. Other scenarios find leakage rates that are within range of previous studies.

These findings show – once again – that people claiming that gas is cleaner than coal within the crucial next few decades are walking on thin ice. The accuracy of this claim amongst other things depends on methane leakage across the supply chain for both fuels, as well as the scrubber efficiency of coal. The margin for errors is slim and if we want a coal to gas switch to have any climate benefit at all, there is an urgent need to scale methane detection to accelerate emissions management practices. For example, reducing US gas leakage system-wide from 3% to 0.2% can reduce as many GHG emissions as removing 40% of the cars off America’s roads. Today’s high gas price means that preventing gas from leaking to the atmosphere is economically more interesting than ever. Gas companies should spend some of last year’s record profits curbing their pollution. The industry needs regulatory action and a methane pollution price tag to effectively do so.

Time is precious: According to the Intergovernmental Panel on Climate Change, today’s concentrations of methane in the atmosphere are higher than at any time in at least 800 000 years and emissions of methane continue to climb. The best way to tackle the methane problem is to rapidly phase out all fossil fuels – and not invest in new gas infrastructure today. Any lifelines for fossil gas, such as alleged “clean” blue hydrogen, are also very difficult to justify on climate grounds.

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^[1] The combustion of methane gas also comes with a health toll: It produces nitrogen oxides (NOx), which are precursors to smog, and small amounts of sulfur, mercury, and particulates. Unconventional gas development can also affect local and regional air quality in other ways.

^[2] Scrubbers are an apparatus that cleans the gases passing through the smokestack of a coal-burning power plant. Most scrubbers in coal plants are used to remove sulfur emissions and lessen the formation of acid rain.

^[3] The IPCC has established a coal mine methane emission factor of 18 cubic meters methane per tonne of coal mined (m3 methane/t).