How green is your city? Towards an index of urban sustainability

How green is your city? Towards an index of urban sustainability

Image of Europe at night from NASA's Marshall Space Flight Center
In this image from NASA's Marshall Space Flight Center, urban centers London, Amsterdam, Brussels and Paris shine brightest...but does that mean they're less efficient than other areas?



There is no definitive list, but we may be moving toward clearer answers to these questions. An exciting body of work is coming up with ways to measure the environmental impact of cities. Let’s look at three.



Ecological footprint is measured in global hectares (gha) per capita. The global average is around 2.6. The footprint of London, for example, was measured at 4.5, slightly lower than the U.K. average of 4.6. More people in London use public transport than almost any other city in the U.K., reducing the relative size of its footprint.

When the data are broken down by neighborhood, the biggest footprints are found in higher-income areas where residents have larger homes and are more likely to have private automobiles. In San Francisco, the value was calculated at 7.1 gha while in Calgary, Canada the value was 9.8 gha. Winters are cold in Calgary, and most people use cars to get around.



One 2010 study measured the carbon footprint of 12 cities: Beijing, Jakarta, London, Los Angeles, Manila, Mexico City, New Delhi, New York, São Paulo, Seoul, Singapore and Tokyo. The number included direct emissions from the metropolitan area, as well as emissions produced in the metro area but consumed elsewhere, such as goods manufactured in cities.

Four of the cities have footprints smaller than the global average: Delhi, Manila, São Paulo and Beijing, in part because of relatively high usage of public transportation. London was close to the global average, while Los Angeles had by far the largest, followed by Singapore, New York and Mexico City.

Another study from 2009 measured the carbon footprint of the largest 100 metro areas in the U.S. and found the higher-density metro areas had the smallest footprint. An even more recent study of all U.S. households found that those in suburban areas had a much higher footprint than those in the larger cities.



Studies that assessed the footprint of Milan, Italy and Lijiang City, China showed how the increasing footprint was straining those cities' water supplies.

Imperfect measures, but a start






This article first appeared at The Conversation.