A satellite captured 5,435 cities for six years and found that most cities with clear trends are getting richer while their fossil-fuel signal is falling. That’s a pretty interesting result because urban climate progress can be pretty hard to verify. Cities publish climate plans, announce low-emission zones, electrify buses, regulate industry, and promise greener growth, but comparing one city with another is difficult because the data are often patchy, inconsistent, or years out of date. A new Nature Cities paper tries to take a bit of a different route. Instead of relying only on city-reported emissions inventories, the researchers looked from space. They used daily measurements of tropospheric nitrogen dioxide from TROPOMI, an instrument on the Sentinel-5P satellite. NO2 is released by combustion-heavy activity such as traffic, power generation, and industry. It doesn’t stay in the atmosphere for long, which makes it useful for detecting relatively local changes in fossil-fuel-dependent activity. Then they matched those satellite trends with city-level GDP per person between 2019 and 2024. In simple terms, they asked whether cities are becoming richer while the satellite-visible signal of local combustion goes down. That matters because cities basically sit at the centre of the global economy. They generate a huge share of GDP, concentrate transport and industry, and lock in infrastructure choices that can last for decades. A city that grows around cars, fossil power, diesel generators, and sprawling land use can be hard to change later. The researchers began with 5,435 cities with more than 100,000 people. For 2,475 of them, the NO2 trend was strong enough to classify with confidence. They sorted those cities into four groups: 1. Cleaner and richer: GDP per person rose while NO2 fell. 2. Dirtier and richer: GDP rose while NO2 rose. 3. Cleaner and poorer: NO2 fell while GDP fell. 4. Dirtier and poorer: NO2 rose while GDP fell. The largest group was cleaner and richer. Around 80% of classified cities landed there. That’s basically the headline finding. Across a large set of cities with clear satellite trends, economic growth often coincided with a falling local combustion signal. China dominates the result. More than 700 Chinese cities were classified as cleaner and richer, including Beijing, Shanghai, Guangzhou, Suzhou, Chengdu, and Jieyang. The likely explanation is a mix of stricter emissions controls, industrial relocation, electrification of public transport, cleaner energy systems, and stronger air-quality policy. Europe shows a similar pattern. Paris, Berlin, Rome, and Amsterdam all appear in the cleaner and richer group, alongside many other European cities where low-emission zones, cleaner transport, and energy policy may be reducing the combustion signal while output keeps rising. North America also appears on the decoupling map. Montreal, Vancouver, Seattle, Denver, Austin, San Jose, and Las Vegas all showed falling population-weighted NO2 while GDP per person rose. That’s the encouraging part of the paper. The warning is in the second group. Around 16% of classified cities were dirtier and richer. These are cities where GDP per person rose, but the satellite signal of combustion-heavy activity rose too. They were concentrated in India, Iran, Russia, the Middle East, and Central Asia. This is the older development path still visible from orbit: more vehicles, more sprawl, more fossil electricity, more industry, and more urban NO2. Cities such as Riyadh, Moscow, Tashkent, Izmir, and Abu Dhabi showed some of the larger NO2 increases among affluent cities. The paper points to rising vehicle use, industrial expansion, fossil-fuel-based electricity, and weaker environmental regulation as likely contributors. Then comes the more painful category: cleaner and poorer. About 4% of classified cities saw NO2 fall while GDP also fell. That can look positive if you only look at pollution, but the geography tells a harder story. Cities such as Khartoum and Kabul appear in this category, along with cities in Lebanon, Sudan, Afghanistan, and Yemen. In these places, falling NO2 may reflect economic contraction, conflict, deindustrialisation, or reduced activity rather than successful green policy. The smallest category is the most concerning. Only 18 cities were classified as dirtier and poorer, but the combination is severe: NO2 rose while GDP per person weakened. The paper finds examples in Iran, Libya, Angola, and India. That pattern can point to inefficient generators, unregulated traffic, polluting industry, and weak economic performance moving together. Intresestingly, the paper avoided relying on night-time lights for GDP. That matters because night-light data can be distorted by sensor limits, LED lighting, and the uneven relationship between brightness and income. Instead, they used subnational GDP estimates and carried uncertainty through the analysis. The caveat is important. NO2 is a proxy. It’s useful for tracking local combustion-heavy activity, but it doesn’t directly measure CO2, total air pollution, water quality, biodiversity loss, or emissions embodied in imported goods. A city can reduce local NO2 while still consuming products made in dirtier places. A city can also reduce NO2 through cleaner engines and filters while total fossil fuel use remains high. So the paper should of course be read carefully. It shows decoupling between economic growth and a satellite-observed combustion signal. It doesn’t prove complete green growth in every environmental sense. Link to paper: nature.com/articles/s44284-0…