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Subject: From ClimateWire -- TRANSPORTATION: Researchers find 'hidden benefits' of electric vehicles -- they can make cities cooler,
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Date: March 20, 2015 at 11:21 AM
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TRANSPORTATION:
Researchers find 'hidden benefits' of electric vehicles -- they can
make cities cooler, healthier
Benjamin Hulac, E&E reporter
Published: Friday, March 20, 2015
The world's most compact and industrial cities, with limited greenery, smothering blacktop and
hardened buildings, amplify climate change effects by trapping and retaining heat. Scientists
describe the phenomenon as the "urban heat island effect," or UHIE. Public health officials
often link its presence to heat wave deaths, and grid operators chart spikes in power surges
and outages on cities' hottest days worldwide.
By examining energy use and heat island intensity in Beijing, a city of 21 million that has come
to represent the brunt of steady global warming, a study published yesterday in Scientific
Reports outlined a man-made response to a man-made problem: electric vehicles.
According to the authors, phasing out conventional cars and trucks for plug-in electric vehicles
in cities that suffer from UHIE would generate a pair of "hidden benefits."
Electric vehicles emit significantly less heat than conventional vehicles, and more EVs would
ease the load on a city's power grid by reducing demand from air conditioners and, in turn,
mitigating heat island intensity, the study found. Heat emitted from air conditioning and
vehicles are the two root causes of UHIE, the authors said.
In 2012 in Beijing, which had 5.2 million vehicles at the time, EVs on average emitted about 20
percent of what conventional vehicles did over the same distance. Swapping them out for their
electrified rivals in the summer of 2012 would have lowered the intensity of the heat island
effect 0.94 degree Celsius.
"Heat waves kill and, in terms of climate change, even 1 degree can make a difference," said
Jianguo Liu, one of the report authors and the director of the Center for Systems Integration
and Sustainability at Michigan State University, in a statement.
and Sustainability at Michigan State University, in a statement.
"It's easy not to see the big picture on issues like electric cars and global warming," he said,
"but when we look with a holistic approach, we find these unexpected connections."
As cities like Beijing cook in the summertime, residents switch on their cooling systems.
In the summer of 2012, the substitution of EVs would also have cut greenhouse gas emissions
for Beijing by about 10,500 metric tons per day by reducing power demand by roughly 14.50
million kilowatt-hours -- electricity specifically for air conditioning.
In their analysis, the authors did not account for any change in the ground surfaces in Beijing,
a root cause of UHIE, but simply replaced the emissions from combustion vehicles with
emissions from electric vehicles in their calculations.
Taking advantage of an 'inevitable trend'
Changing street and sidewalk surfaces, growing public transit systems and expanding green
spaces, such as parks, are all methods to address heat island effects.
But, Liu said, the impacts of shifting to more EVs may be more significant and practical than
other options.
"Because land in cities is [pricey] and there are huge demands for the limited land, there is a
limit in terms of how much more green space can be added and how much surfaces of the
cities can be changed," Liu said in an emailed response. "Even with increasing public transit, it
is still more convenient to use individual vehicles under many circumstances."
Plug-in electric cars will eventually replace conventional gasoline and diesel automobiles,
according to the researchers, who call such a transition an "inevitable trend around the world."
But, they note, EVs require more energy to manufacture than combustion engine vehicles.
China is the world's biggest carbon emitter. It unloaded about 8.25 megatons' worth of heattrapping gases in 2012, according to the International Energy Agency, approximately a quarter
of global emissions for that year. The global tally in 2012 was roughly 32 megatons. (One
megaton equals 1 million metric tons.)
Yet the positive byproducts from more plug-in cars and trucks in cities could be far greater than
the study indicates, Liu said.
"We were surprised by the hidden effects and their magnitudes even in one city," he said of his
peers and their results. "Globally, the effects would be much larger."
While China remains one of the biggest economic engines that drive the global economy, it is
certainly not the only country whose citizens suffer from the heat island effect.
A separate study published in late January concluded that heat waves have grown
increasingly common in the last 40 years and are at their worst in urban areas.
increasingly common in the last 40 years and are at their worst in urban areas.
Dennis Lettenmaier, a geography professor at the University of California, Los Angeles, and
his co-authors studied the heat patterns of 217 urban areas worldwide from 1973 to 2012 and
concluded that periods of extreme heat "increased significantly" in 48 percent of those cities
during that period.
More than half of the world lives in cities, a shift from the decades following World War II. As
emerging economies expand, that ratio is projected to only get more lopsided, according to
many demographic projections.
According to U.N. analysis released in 2011, 59 percent of humans will live in urban areas by
2030. Cities today account for about 70 percent of the greenhouse gas emissions but cover 2
percent of the world's surface.
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