Natural gas has long been promoted as a cleaner alternative to coal and oil, particularly in China’s rapidly expanding cities. Its combustion produces less particulate pollution and generally lower carbon dioxide emissions than coal, helping improve urban air quality. Yet a new study suggests that the climate benefits of this transition may have been seriously overstated because large quantities of methane are escaping before natural gas reaches consumers. Researchers studying the Yangtze River Delta metropolitan cluster have found that methane leakage from the region’s natural gas supply chain is far higher than the rate used in China’s official inventories. Their findings indicate that the apparent shift toward cleaner energy may carry a much larger warming penalty than previously recognized.

The study, published in Nature Cities, reconstructs natural gas-related methane emissions using a decade of atmospheric observations collected between 2012 and 2021. Instead of attempting to measure methane releases directly from every pipeline, storage facility, distribution network and end-use system, the researchers focused on ethane, or C₂H₆, a hydrocarbon that provides a distinctive chemical fingerprint for fossil fuel emissions. Ethane is commonly found alongside methane in natural gas, but it is not produced in significant amounts by many other major methane sources, such as wetlands, livestock or rice cultivation. Tracking ethane therefore allows scientists to identify and quantify emissions associated specifically with fossil fuel use.

The Yangtze River Delta offers an especially important setting for this investigation. The densely populated metropolitan cluster includes major cities, extensive industrial activity and one of China’s most developed natural gas consumption networks. Over the past decade, natural gas use in Chinese cities has nearly tripled as households, industries and power systems have moved away from more polluting fuels. That transformation has delivered visible benefits for air quality, but it has also expanded the infrastructure through which methane can leak. Emissions may occur during gas processing and transmission, through distribution pipelines, at pressure-regulation equipment, or during storage and consumption. Even relatively small losses at numerous points can accumulate into a substantial regional source.

To determine how much gas was escaping, the researchers combined long-term ethane measurements with atmospheric model simulations. The models describe how emissions are transported and diluted by wind and other atmospheric processes, allowing the team to compare expected ethane concentrations under different leakage assumptions with the concentrations actually recorded. The critical test was whether one estimate could explain both seasonal changes and long-term trends in atmospheric ethane over the full ten-year period. According to the study, a natural gas leakage rate of 3.5 percent was required to reproduce the observations, with an estimated range of 2.5 to 4.3 percent.

That result is dramatically higher than the 0.2 percent leakage rate commonly assumed in China’s inventories. The difference is not a minor adjustment. A leakage rate of 3.5 percent means that roughly one molecule of natural gas out of every thirty is lost somewhere between the supply system and final use, although the study’s estimate represents an average for the relevant consumption-related supply chain rather than a direct measurement at a single facility. Because methane is exceptionally effective at trapping heat in the atmosphere, such losses can substantially reduce or even undermine the climate advantage expected from replacing coal with natural gas.

Methane is the primary component of natural gas and is a powerful greenhouse gas, especially over the first several decades after it enters the atmosphere. Its atmospheric lifetime is much shorter than that of carbon dioxide, but its warming effect during that period is far stronger. This makes methane leakage a particularly important factor in near-term climate change. Natural gas combustion may emit less carbon dioxide than coal for the same amount of energy, but that advantage depends on keeping losses from production, transport and distribution under control. If enough methane escapes unburned, the climate benefits of using gas instead of coal can shrink considerably.

Using the estimated leakage rate, the researchers calculated that natural gas consumption in the Yangtze River Delta produced average methane emissions of approximately 0.68 teragrams per year between 2012 and 2021. The uncertainty range extends from 0.48 to 0.83 teragrams annually. A teragram is one million metric tons, meaning the estimated emissions represent hundreds of thousands of tons of methane released into the atmosphere every year. The study indicates that these emissions have been substantially underestimated or entirely omitted in existing inventories. Such omissions can distort national and regional climate assessments, making it difficult for policymakers to identify where methane reductions could be achieved most effectively.

The use of ethane was central to the researchers’ conclusions because methane alone cannot reliably reveal its origin. Atmospheric methane comes from a mixture of natural and human sources, and concentrations can rise because of wetlands, agriculture, waste, fossil fuels or changes in atmospheric chemistry. Ethane acts as a companion tracer for emissions from fossil fuel systems. By examining ethane variability over time and comparing it with atmospheric transport simulations, the scientists were able to separate the signal linked to natural gas consumption from the much larger background of other methane sources. The long observation period also helped them distinguish persistent leakage from short-lived events and assess whether the estimated rate remained consistent with changing gas use.

The findings arrive as China and other countries expand gas infrastructure while pursuing cleaner urban energy systems. They do not suggest that reducing coal use has no value: natural gas combustion generally produces less soot, sulfur dioxide and many other air pollutants than coal combustion. However, the study shows that air-quality gains and climate gains are not identical. A fuel can improve local air pollution while still creating a significant warming impact if its supply chain is poorly controlled. The researchers argue that methane budgets should therefore be reassessed at the sector and regional levels, particularly in rapidly urbanizing areas where gas demand is rising quickly.

The study also points to practical priorities for reducing emissions. Improved leak detection, frequent inspections, rapid repair of faulty equipment and better measurement of distribution systems could help identify the sources responsible for the unexpectedly high rate. Technologies such as mobile methane sensors, aircraft surveys, satellites and continuous monitoring networks could complement atmospheric ethane observations by locating individual emission hotspots. More accurate inventories would allow regulators to evaluate whether natural gas is delivering the climate performance expected of it and would provide a stronger basis for comparing gas with renewable energy, electrification and other alternatives. As cities continue to consume more natural gas, the researchers’ message is clear: counting only the fuel that reaches the burner is no longer enough. The climate cost of the gas lost along the way must also be included.

Subject of Research: Methane emissions and natural gas supply-chain leakage in the Yangtze River Delta metropolitan cluster of China.

Article Title: Underestimated methane emissions from natural gas consumption in the Yangtze River Delta cities of China.

Article References: Zhao, Y., Zhang, Y., Zhang, Y. et al. Underestimated methane emissions from natural gas consumption in the Yangtze River Delta cities of China. Nat Cities (2026). https://doi.org/10.1038/s44284-026-00504-1

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s44284-026-00504-1

Keywords: methane emissions, natural gas leakage, ethane observations, Yangtze River Delta, China, urban air quality, climate change, fossil fuels, atmospheric modeling, greenhouse gases

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