A new study by NASA and U.S. universities on carbon dioxide emissions for the 20 largest cities around the world provides the first direct, satellite-based evidence that carbon dioxide emissions decrease per person as the city's population density increases.
According to a release from NASA's Jet Propulsion Laboratory (JPL) on Friday, the survey also shows how satellite measurements can track carbon dioxide emissions to rapidly fast-growing cities and evaluate the effectiveness of policy changes and infrastructure improvements on their energy efficiency.
Cities account for more than 70 percent of global carbon dioxide emissions related to energy production, and fast, underway urbanization is increasing their numbers and size. However, some densely populated cities release more carbon dioxide per capita than others.
Atmospheric scientists Dien Wu and John Lin of the University of Utah in Salt Lake City have joined with colleagues at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Michigan in Ann Arbor.
They computed the per capita carbon dioxide emissions in 20 cities areas on different continents using the recently available carbon dioxide guesses from NASA's Orbiting Carbon Observatory-2 (OCO-2) satellite.
Researchers used satellite-obtain estimates of the amount of carbon dioxide present in the air above an urban area as satellite overhead flies.
Lin said, "Other people have used fuel statistics, the number of miles driven by a person or how big people's houses are to compute per capita emissions." He also said, "We're looking down from space to actually measure the carbon dioxide concentration over a city."
Published February 20 in the Environmental Research Journal, the survey found that cities with a high population density generally have high carbon-dioxide emissions per capita.
The researchers trust new data from OCO-2's inheritor, OCO-3 -- which was launched to the International Space Station last year -- along with future space-based carbon dioxide-watching missions, which may shed light on strong solutions to alleviate cities' carbon emissions.