Satellites Don't Hide

Research findings show that urban methane (CH₄) emissions presented by governments in official statistics have been reduced to less than half of actual levels. According to a paper published by researchers from the University of Michigan's College of Engineering in the Proceedings of the National Academy of Sciences (PNAS), methane emissions from 92 major cities worldwide increased by approximately 6% between 2019 and 2023. In contrast, official inventory estimates from governments increased by only 1.7% to 3.7% during the same period. The gap between satellite data and official statistics has been obscuring the reality of actual emissions.

The research team utilized satellite observation-based top-down measurement methods with support from NASA and the National Institute of Standards and Technology (NIST). Unlike existing official statistics that rely on bottom-up accounting methods, which sum individual emission source data, satellites directly measure actual atmospheric concentrations.

Why It Matters: The Carbon Neutrality Clock Is Wrong

Methane is a greenhouse gas approximately 80 times more potent than carbon dioxide (CO₂) on a 20-year basis. Given its significant short-term climate change mitigation effect, methane reduction is considered a key means of achieving 2030 climate goals.

The problem is that cities account for approximately 10% of total anthropogenic methane emissions. This is about 4 times the scale of 'excess emission sources' in the oil and gas sector that have been under intensive regulatory scrutiny. The research team revealed that member cities of the 'C40 Climate Group,' a coalition of climate action cities, are emitting an additional 2 teragrams (Tg) of methane annually. This figure directly contradicts the carbon neutrality plans these cities have declared for themselves.

Clear regional differences emerged. European cities show a declining emission trend due to infrastructure modernization and strengthened regulations, while cities in Asia, Africa, and South America are experiencing increased emissions driven by aging gas pipeline networks, inadequate landfills, and underdeveloped wastewater treatment systems.

When Did This Begin: A History of Climate Statistics Distrust

The reliability of urban greenhouse gas statistics has been a long-standing debate. Since the mid-2000s, the climate science community has pointed out the limitations of existing top-down estimation methods. Particularly with the shale gas boom starting in the 2010s, numerous studies showed that methane leakage in the United States reached several times the EPA's official figures.

The improved precision of satellite-based measurement technology is relatively recent. With the advent of the European Space Agency's (ESA) Sentinel-5P satellite (launched in 2017) and private satellites like GHGSat, precise city-level methane observations became possible starting in the 2020s. This University of Michigan research is one of the first large-scale studies to systematically demonstrate the structural underestimation of urban emission statistics by utilizing this technological advancement.

There is also context from the international climate agreement perspective. The 'Global Methane Pledge,' signed by the United States, EU, and approximately 100 other countries at COP26 in 2021, includes a goal to reduce methane emissions by 30% compared to 2020 levels by 2030. However, if the baseline emission levels themselves have been underestimated, the determination of whether reduction targets are met becomes fundamentally uncertain.

Future Outlook [Expert Analysis]

This research is likely to have three major impacts.

First, discussions on strengthening the verification system of international climate agreements are likely to accelerate. Pressure to amend the agreement will likely increase, moving toward mandatory integration of satellite observation data with the current United Nations Framework Convention on Climate Change (UNFCCC) verification method, which relies solely on national reporting data.

Second, the priorities for urban infrastructure investment are likely to be reorganized. Gas pipeline replacement, landfill methane capture facilities, wastewater treatment plant modernization, and similar projects could emerge as key items in carbon neutrality budgets. In particular, the demand for green infrastructure in developing country cities is expected to surge.

Third, there are also significant implications for Korea. Major Korean cities such as Seoul, Incheon, and Busan are also participating in the C40 Network or similar international climate agreements. Since domestic greenhouse gas emission statistics also rely on bottom-up estimation methods, there is a high likelihood that calls will emerge for the Ministry of Environment and local governments to consider adopting satellite-based verification systems. Independent verification requests regarding the Capital Area landfill issue and methane leakage from aging city gas pipelines are also likely to be raised.