Density does not reliably predict per capita carbon dioxide emissions
Cities will save us, experts argue. Higher densities of people mean less energy consumption and lower carbon emissions per capita—a boon for
the environment. People supposedly switch from driving cars to using
public transportation, for instance. But “density in and of itself isn't
changing behavior,” says Conor Gately, a graduate student in Boston
University's department of Earth and environment. Gately and his
colleagues analyzed 33 years' worth of annual carbon dioxide emissions
by on-road vehicles across the U.S. Since 2000 the 50 fastest-growing
counties by population decreased their per capita emissions by only 12
percent—a reduction that was not enough to offset the total emissions
growth in those same areas. The discrepancy probably comes down to the
sprawl of suburbs, the researchers say. If public transportation between
city and surrounding neighborhoods, for example, fails to keep pace
with growth, more and more people will drive into center cities for work
and play and add pollution to areas where they don't live. (That's
what's been happening in Salt Lake City.)
Urban areas that are already dense and have the necessary green
infrastructure, such as New York City, will see their per capita
emissions decline as they grow larger. In 2012 carbon emissions from
vehicles on the road accounted for 28 percent of the total fossil-fuel
CO2 emissions for the entire country—a sizable chunk to
target for reductions. The data suggest that solutions and regulations
should be customized for individual cities, not mandated as national
catchalls.
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