levels. An all-hybrid fleet, combined with the first smart-growth scenario, could drop emissions another 4%; a highly mobile lifestyle has inand if it were combined with the Replacing all existing cars with hycreased the number of miles travsecond smart-growth scenario, emisbrid electric ones can significantly eled. Since the 1960s, we’ve sions could come down another 6%. reduce greenhouse gas emissions, reduced tailpipe emissions of reguBy 2050, the more aggressive smartbut curbing urban sprawl and enlated pollutants by as much as growth policies in conjunction with forcing smart-growth measures can 90%, but we’ve also more than an all-hybrid fleet could reduce proknock those emissions down a notch tripled our vehicle miles traveled, jected emissions under the businessfarther, according to a study pubhe notes. as-usual scenario by 25%. lished in ES&T (DOI 10.1021/ “We show that it’s critical es8021655). The study is the to have both technology and first to investigate the longland-use policies to deal with term impacts of combining CO2 because we won’t be smart-growth measures and hybrid electric cars across able to reach Kyoto [Protoseveral metropolitan areas in col]-like targets without six states in the midwestern [both],” says Stone. The inU.S. ternational Kyoto Protocol “In general, there are on climate change sets bindthree main strategies that ing targets for 37 industrialpeople talk about for reducized countries that require ing motor vehicle greenPer capita fuel consumption and carbon emissions are lower them by 2012 to reduce house emissions,” says Julian in more compact and densely populated cities like New emissions by an average of Marshall, who is an environ- York. 5% of their 1990 reported Policies that prevent urban sprawl mental engineer at the University of emissions. The U.S. has yet to ratify and create densely populated cities Minnesota and was not associated the protocol. with good public transport systems, with this study. One is improving “I like the study,” says Michael and pedestrian- and bicycle-friendly vehicle fuel efficiency, for example Chang, an atmospheric scientist also urban designs, bring down the numby switching to hybrid electric cars. at the Georgia Institute of Technolber of miles traveled per vehicle, thus The second is converting to a lowogy. “It’s a good start on a lot of reducing the emissions. In a Viewcarbon fuel. The third approach, questions” that are going to be raised point published last May in ES&T Marshall says, combines measures now that the U.S. is making climate (DOI 10.1021/es087047l), Marshall such as smart-growth policies (laws change a high priority. However, it is argued that well-planned, energyand regulations that help create more of a “sensitivity analysis” than efficient urban landscapes could play more compact, densely populated a “value assessment,” Chang adds. an important role in mitigating clicities like Portland, Ore.) with meaFor example, the study does not asmate change. sures that encourage walking, biking, sess whether replacing the existing In the new study, Stone and his and increased use of public transfleet with hybrid electric vehicles will colleagues modeled the emission port. This approach controls the be economically feasible or difficult levels between 2000 and 2050 under number of “vehicle miles traveled,” to implement. Stone agrees. The three development scenarios: busiwhich is actually a measure of transstudy is not a “forecast,” he warns. ness as usual (in this case, they used portation activity, he says. “We’re not predicting this is going to census tract data on population, so“Most of the research on adhappen. But if it did happen, then cioeconomic, and land-use changes dressing climate change has fohow much would vehicle travel and from 1970 to 2000); a smart-growth cused on vehicles and fuels,” says CO2 [emissions] change?” scenario akin to one already impleMarshall. Similarly, federal regula—RHITU CHATTERJEE mented in Portland; and a second, tions have focused on cutting emismore aggressive, hypothetical smartsions at the tailpipe, adds Brian growth scenario with an even larger Stone, corresponding author of the population concentrated into urban new study and an expert on urban and suburban areas. They then comenvironmental management at the pared these scenarios with projected Georgia Institute of Technology. emission levels for a hybrid electric Switching to more fuel-efficient vehicle fleet. cars will definitely cut emissions An entire fleet of hybrid electric per mile traveled, he notes. “But vehicles in 2050 could reduce averthat only takes you so far.” That is age emissions of CO2 back to 2000 because a growing population with ISTOCKPHOTO
Smart growthsa solution to climate change?
1660 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / March 15, 2009
10.1021/es900293g
2009 American Chemical Society
Published on Web 02/10/2009
