An innovative study used data from the OCO-3 satellite of the NASA to measure carbon dioxide emissions in 54 global cities.
It was discovered that Tokyo, Japan, tops the ranking with 83 million metric tons annually.
In contrast, Rotterdam, Netherlands, records the lowest number, with 11 million.
How NASA’s analysis works to measure city emissions
The research employed the Orbiting Carbon Observatory-3 (OCO-3) instrument over 4.2 years to obtain independent measurements of urban CO₂ emissions.
This “top-down” approach contrasts with traditional inventories that rely on fuel consumption data.
The 54 cities analyzed collectively emit 1,735 million tons of CO₂ per year, a figure comparable to Russia’s emissions.
The study found that urban cities concentrate approximately 75% of the global carbon emissions.
Another interesting fact is that emissions in Africa are underestimated when compared to the EDGAR and ODIAC inventories.
Lower values than these measurements are also recorded in Europe, North America, and East and Southeast Asia. Conversely, they overestimate the figures in Central and Eastern Asia.
Carbon footprint of major cities: the most surprising data
The socioeconomic analysis reveals a clear pattern: per capita emissions decrease as population size increases.
Cities with fewer than 5 million inhabitants emit 7.7 tons of CO₂ per person.
This figure drops to 1.8 tons in cities with more than 20 million inhabitants, a 77% reduction.
The greater population density and efficient public transport explain this trend.
On the other hand, comparing the size of the GDP per capita of each city with their carbon footprints shows that high-income areas exhibit less carbon-intensive economies.
For example, North American cities emit 0.1 kg of CO₂ per dollar of economic output, while African cities emit 0.5 kg per dollar.
This inverse relationship between GDP per capita and carbon intensity suggests that economic development can be decoupled from emissions when clean technologies are implemented.
The contribution of NASA’s study to global commitments
More than 1100 cities committed to halving their emissions by 2030 through the United Nations’ “Race to Zero” campaign.
In light of this goal, this study provides an independent verification tool to monitor progress.
Satellite measurements primarily capture Scope 1 emissions, which represent 61% of the total greenhouse gases in the analyzed C40 cities.
The integration of satellite data with local and global inventories is essential to build a robust accounting of urban CO₂ emissions and support net-zero emissions goals.
