8 • The Southwest Portland Post
Dear EarthTalk: Isn’t the increasing
urbanization of our world good for
reducing our carbon footprint given
the efficiency benefits of greater
density?
– Simon Vorhees, Oak Park, Illinois
No doubt, the increased density of
big cities leads to less energy use and
fewer greenhouse gas emissions per
capita.
“The biggest factor is transportation,
first, simply because trips get shorter,
and second, because trips are more
likely taken by transit, biking and
walking, which are more energy
efficient than cars,” said Dan Bertolet
of Sightline Institute, a Seattle-based
sustainability think tank.
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“Density also leads to less energy
use in buildings for two reasons:
The housing tends to be smaller, and
the shared walls/floors/ceilings in
multifamily buildings help conserve
heating and cooling.”
To Bertolet’s point, a recent study
published in the Proceedings of
the National Academy of Sciences
examining projected emissions from
buildings in a variety of urban areas
confirms that denser development is
more effective at reducing greenhouse
g a s e m i s s i o n s t h a n w e a t h e r-
proofing or other efficiency-oriented
infrastructure upgrades.
But researchers warn that increased
density alone isn’t enough to drive
emissions lower overall given a host
of other factors.
“Urbanization is often accompanied
by higher incomes, higher economic
activity and more consumption,”
said Burak Güneralp, geosciences
researcher at Texas A&M University
and the study’s lead author.
“So any gains in per capita
consumption due to greater density
in urban areas may be exceeded by
the increase in per capita consumption
due to higher incomes.”
Also, said Güneralp, efficiency
benefits of increased density can
backfire if not directed by thoughtful
policy. “For example, too high a
density coupled with poor planning
March 2017
San Francisco, with upwards of 18,000 people per square mile, is the second densest
major U.S. city behind New York. (Photo by Dave Glass, FlickrCC )
can lead to traffic congestions, which
can increase fuel consumption hence
carbon emissions.”
Another downside of density is the
so-called “heat island effect,” where
development-crammed, pavement-
capped city centers can be some 20
degrees hotter than surrounding
areas.
This leads to increased energy
consumption as more people crank the
air conditioning, elevated emissions of
potentially hazardous air pollutants
from tailpipes and outflow stacks, and
impaired water quality as streams,
rivers, lakes and coastal areas get
flushed with overheated toxin-laden
run-off.
Poorly managed development
outside the urban core, a.k.a. urban
sprawl, can also counteract the carbon
footprint gains of increased density
downtown.
Sprawling suburban development
uses more land per capita and forces
people to drive long distances in
private cars to get to work, school and
shopping.
“Metropolitan areas look like carbon
footprint hurricanes, with dark green,
low-carbon urban cores surrounded
by red, high-carbon suburbs,” said
Chris Jones, a researcher with UC
Berkeley’s Renewable & Appropriate
Energy Lab.
“Unfortunately, while the most
populous metropolitan areas tend
to have the lowest carbon footprint
centers, they also tend to have the
most extensive high-carbon footprint
suburbs.”
For his part, Güneralp said careful
planning is key. “The important
point is that when we think about
urbanization and its environmental
impacts, we need to consider trade-
offs and co-benefits of different
approaches as well as the local
context,” he concluded.
“Particularly in growing cities in
the developing world, such efforts
can improve the well-being of billions
of urban residents and contribute to
mitigating climate change by reducing
energy use in urban areas.”
Contacts: Sightline, www.sightline.
org; National Academy of Sciences
s t u d y, w w w. g o o . g l / s x q H 0 E ;
Renewable & Appropriate Energy
Lab, www.rael.berkeley.edu.
EarthTalk® is produced by Roddy
Scheer & Doug Moss and is a registered
trademark of the nonprofit Earth Action
Network. To donate, visit www.earthtalk.
org. Send questions to: question@
earthtalk.org.
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