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Indianapolis, Indiana, is the Midwest city. A 2026 Journal of Geophysical Research study estimates that natural-gas-sector methane emissions equal about 1.6% to 2.4% of residential and commercial gas consumption there—often rounded to roughly 2% of gas piped into the city.
What the 2% estimate actually means
The figure is an atmospheric loss fraction, not a claim that 2% of every household bill is visibly leaking at any given moment. It compares methane released across the Indianapolis urban area with the amount of residential and commercial natural gas consumed or supplied during the study period.
Natural gas is mostly methane. The study’s best estimate spans 1.6% to 2.4%; Penn State summarized the result as “about 2% of all natural gas piped into Indianapolis.” The range reflects uncertainty in atmospheric transport, background methane, wind conditions, the modeled boundary and other factors.
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How scientists measured methane across Indianapolis
Tall towers supplied continuous observations
Researchers used a network of tall towers to measure methane concentrations continuously across the city. The principal analysis covered January 2014 through December 2023. The wider INFLUX observation network operated from 2011 into 2025, providing a longer context for urban greenhouse-gas measurements.
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Atmospheric inversion linked concentrations to sources
Measurements alone show how much methane is in the air, not exactly where it was released. The team combined tower readings with atmospheric-transport modeling and Bayesian inversion. That approach tests how emissions from different parts of the city would move with the observed winds, then estimates the source strength that best explains the measurements.
This is called a top-down estimate because it starts with atmospheric concentrations. It differs from a bottom-up inventory, which adds estimated emissions from equipment, facilities and activities.
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Where the methane probably comes from
The methane signal was diffuse across Indianapolis rather than concentrated only along major exterior pipelines. Indianapolis has nearly 0% leak-prone pipe before the customer meter, because its pre-meter distribution network is largely modern plastic pipe. On that evidence, the study argues that most diffuse natural-gas emissions probably occur after the meter.
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That conclusion does not mean every building has a dangerous leak or that a particular appliance has been identified as the source. It means citywide atmospheric observations are more consistent with dispersed post-meter emissions than with widespread leakage from older underground distribution pipe.
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The South Side Landfill is a separate methane source
Indianapolis also contains the South Side Landfill, which the 2026 study treats as the city’s largest single point source of methane. It should not be folded into the roughly 2% natural-gas leakage figure. The landfill is a non-gas methane source analyzed separately from the diffuse source associated with natural-gas use.
Why the Indianapolis estimate is higher than some inventories
A 2020 INFLUX analysis found that inverse-model emissions remained about 91% higher than inventory estimates even after the modeled city domain was made consistent with the inventory domain. Its atmospheric budget put the diffuse natural-gas source about 70% above inventory estimates.
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Several technical choices can produce that gap:
- Atmospheric models must account for background methane entering the city and for changing wind direction.
- Results depend on the geographic domain used for the calculation.
- Time-of-day patterns can affect how observations represent emissions.
- Inventories may omit or undercount diffuse post-meter and end-use releases.
A higher top-down estimate is therefore not automatically proof that a specific pipeline operator or appliance category is responsible. It indicates that the measured citywide methane budget is larger than the emissions represented in the inventory.
How this compares with national direct measurements
| Estimate | What was measured | Result | What it leaves out or qualifies |
|---|---|---|---|
| Indianapolis, 2026 study | Continuous tower methane observations interpreted with atmospheric transport and Bayesian inversion | 1.6%–2.4% of residential and commercial gas consumption; commonly rounded to about 2% | City-scale, top-down estimate; includes diffuse emissions and depends on modeled boundary and atmospheric conditions |
| United States, NIST study published 2015 | Direct sampling of 230 underground pipeline leaks and 229 metering and regulating facilities | 393 Gg of methane per year; 95% upper confidence limit of 854 Gg/year; equivalent to 0.10%–0.22% of methane delivered to customers nationwide for those categories | Lower bound: excludes other urban sources, including many possible end-use emissions |
These percentages cannot be compared as if they measured the same thing. Indianapolis uses a top-down city budget that can capture diffuse post-meter emissions. The national NIST result is a bottom-up, direct-measurement estimate for selected infrastructure categories.
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Why methane leakage matters for climate
Methane has a much stronger warming effect than carbon dioxide over shorter time horizons. Using the 100-year comparison cited by the study and Penn State, methane has about 28 times the radiative impact of carbon dioxide. That makes reductions in methane leakage a near-term climate opportunity even when the leaked volume is a small percentage of total gas throughput.
Lead author Zachary Barkley described a 2% loss rate as “massive from a climate standpoint.” The climate implication follows from both the percentage and the fact that the gas is methane released before it can provide useful energy.
What Indianapolis residents and policymakers should take from the result
- The estimate is citywide, not a diagnosis of any individual home.
- Because the likely source is mostly post-meter, reducing emissions may require attention to building piping, appliances and other end-use equipment, not only street-level distribution lines.
- Further measurements that combine tower data with building-level inspections could help identify which post-meter sources dominate.
- Landfill methane-control work is relevant to Indianapolis’s overall methane budget but is a separate issue from natural-gas leakage.
For comparisons with another city or study, check five things first: whether the estimate is top-down or bottom-up, whether it covers pre-meter infrastructure or post-meter use, what geographic boundary and denominator are used, which years were observed, and whether non-gas sources such as landfills were separated.
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