Indianapolis, Indiana, is the Midwest city in question. A 2026 Journal of Geophysical Research study estimates that methane emissions associated with the city’s residential and commercial natural-gas use equal 1.6% to 2.4% of consumption. That is commonly rounded to about 2% of the gas piped into Indianapolis.
The estimate comes from a decade of continuous measurements at tall towers, combined with atmospheric-transport modeling and Bayesian inversion. It is a citywide atmospheric loss estimate—not a claim that 2% of every household’s gas is visibly escaping from a pipe at a particular moment.
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What the “about 2%” figure actually measures
The study’s principal analysis covers January 2014 through December 2023. It estimates the fraction of residential and commercial gas consumption represented by methane released into the atmosphere across the Indianapolis urban domain: 1.6% at the low end and 2.4% at the high end.
Penn State’s summary expresses the result more simply: about 2% of all natural gas piped into Indianapolis is eventually leaked. The two descriptions use different levels of precision. The 1.6%–2.4% range is the study’s estimate; “about 2%” is a rounded public-facing explanation.
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This percentage is a loss fraction over the study area and period. It does not mean that a meter reading is wrong by 2%, that every building has a detectable leak, or that 2% of a monthly bill is escaping at once. Methane can be released in small amounts from many sources and dispersed by wind before it is measured downwind.
How scientists measured methane across the city
Indianapolis is part of the INFLUX urban greenhouse-gas observing network. The broader network operated from 2011 into 2025, while the analysis behind the current estimate uses the most consistent decade of observations.
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- Continuous tower observations: Instruments on a network of tall towers measured methane concentrations over time at multiple locations around the metropolitan area.
- Atmospheric transport calculations: Researchers modeled how winds and atmospheric mixing carried methane from possible source areas to each tower.
- Bayesian inversion: The team used the measured concentrations and transport model to infer the emissions pattern most consistent with the observations, including a diffuse natural-gas-related source spread across the city.
- Domain and background checks: The analysis accounted for the city boundary, changing wind directions, background methane entering the domain and time-of-day patterns before converting the inferred emissions into a percentage of gas consumption.
This is called a top-down approach: it starts with what is in the atmosphere and works backward to estimate the sources. It can capture emissions that equipment-by-equipment inventories miss, but its precision depends on wind fields, background concentrations, the chosen boundary and how other methane sources are represented.
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The diffuse methane signal appears across Indianapolis rather than at one dominant gas-infrastructure point. The study notes that the city has nearly 0% leak-prone pipe before the customer meter, largely because its pre-meter distribution network uses modern plastic pipe. That makes large leaks from older exterior distribution mains a less likely explanation for most of the diffuse signal.
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Researchers therefore conclude that most of the natural-gas-related emissions likely occur after the meter, inside homes and other buildings. Potential pathways include interior gas piping, furnaces, water heaters, stoves and other end-use equipment. The atmospheric result cannot identify a particular house or appliance, and it does not establish that every post-meter component leaks; it indicates that aggregate post-meter emissions are the most plausible explanation for the citywide pattern.
The South Side Landfill is a separate source
Indianapolis also has a major methane point source at the South Side Landfill. The 2026 analysis treats the landfill as the city’s largest single point source while analyzing the diffuse natural-gas source separately. The landfill should not be added to, or mistaken for, the roughly 2% natural-gas leakage estimate.
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Why the estimate is higher than some inventories
Atmospheric estimates and conventional inventories answer different questions. An inventory totals reported or modeled emissions from specified equipment categories. A tower-based inversion measures the methane actually affecting the urban atmosphere and then allocates it among sources.
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|---|---|---|
| Method | Top-down tower observations plus atmospheric transport and Bayesian inversion | Bottom-up equipment measurements, activity data and emission factors |
| Source coverage | Diffuse urban natural-gas emissions, including likely post-meter end use | Only the categories included in the inventory or survey |
| Geography | Indianapolis urban domain | Defined inventory or national source categories |
| Key sensitivity | Background methane, wind direction, domain boundary and time of day | Whether all relevant sources and leakage rates are represented |
A 2020 INFLUX analysis found that, even after making the modeled city domain consistent with the inventory domain, inverse-model emissions were about 91% higher than inventory estimates. Its atmospheric budget put the diffuse natural-gas source about 70% above the inventory estimate. The discrepancy does not by itself prove that one method is universally correct; it shows that unmeasured or underestimated urban sources can materially change the total.
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How the Indianapolis result compares with national direct measurements
A 2015 NIST study directly sampled 230 underground pipeline leaks and 229 metering and regulating facilities across the United States. It estimated 393 gigagrams of methane per year from those source categories, with a 95% upper confidence limit of 854 gigagrams per year. Expressed as a share of methane delivered to customers nationwide, that was 0.10% to 0.22%.
That national figure is not a direct alternative measurement of Indianapolis’s 1.6%–2.4%. The NIST work covered selected pre-meter infrastructure categories and explicitly described its estimate as a lower bound because it excluded other urban sources, including emissions that can occur after the customer meter. The Indianapolis study includes the broader diffuse signal detected in the atmosphere.
Why a small percentage matters for climate
Methane is the main component of natural gas and has a much stronger warming effect than carbon dioxide over the time horizons used in climate accounting. The Penn State summary and the 2026 paper cite a 100-year global-warming potential about 28 times that of carbon dioxide, based on IPCC and EPA data.
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That is why lead author Zachary Barkley described 2% leakage as “massive from a climate standpoint.” Preventing methane releases can reduce near-term warming while also preserving gas that was extracted, transported and paid for. The study does not assign a dollar cost to Indianapolis’s emissions or identify a single repair program that would eliminate them.
What this study can—and cannot—tell residents
- It can show: Indianapolis has a citywide methane signal consistent with natural-gas emissions equal to roughly 1.6%–2.4% of residential and commercial consumption over the study period.
- It can suggest: Because pre-meter leak-prone pipe is nearly absent, diffuse emissions probably arise mainly inside buildings and from end-use equipment.
- It cannot show: Which individual building, appliance or pipe is responsible for a particular plume.
- It does not include by implication: The South Side Landfill in the natural-gas percentage; that source is analyzed separately.
- It should not be compared without context: Other cities’ percentages may use different boundaries, denominators, observation periods, source categories or methods.
The most defensible reading is therefore specific: long-term atmospheric observations indicate that Indianapolis loses methane associated with natural-gas use at a rate near 2% of consumption, with the evidence pointing mainly to post-meter urban emissions rather than a single failing pipeline network.
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