A new study of NASA and U.S. universities on carbon dioxide emissions for 20 major cities around the world has provided the first direct, satellite-based evidence that as a city's population density increases, the carbon dioxide emission per person declines.
According to a release of NASA's Jet Propulsion Laboratory (JPL) on Friday, the study also demonstrates how satellite measurements can give fast-growing cities new tools to track carbon dioxide emissions and assess the effect of policy changes and infrastructure improvements on their energy efficiency.
Cities account for more than 70 percent of global carbon dioxide emissions associated with energy production, and rapid, ongoing urbanization is increasing their number and size. But some densely populated cities emit more carbon dioxide per capita than others.
Atmospheric scientists Dien Wu and John Lin of the University of Utah in Salt Lake City teamed with colleagues at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Michigan in Ann Arbor.
They calculated carbon dioxide emissions per capita for 20 urban areas on several continents using recently available carbon dioxide estimates from NASA's Orbiting Carbon Observatory-2 (OCO-2) satellite.
Researchers used satellite-derived estimates of the amount of carbon dioxide present in the air above an urban area as the satellite flies overhead.
"Other people have used fuel statistics, the number of miles driven by a person or how big people's houses are to calculate per capita emissions," Lin said. "We're looking down from space to actually measure the carbon dioxide concentration over a city."
Published Feb. 20 in the journal Environmental Research Letters, the study found that cities with higher population densities generally have lower carbon dioxide emissions per capita.
The researchers believe new data from OCO-2's successor, OCO-3 -- which was launched to the International Space Station last year -- along with future space-based carbon dioxide-observing missions, may shed light on potential solutions to mitigating cities' carbon emissions.