More than half of the world’s population lives in cities and that percentage continues to rise, making cities critical areas for adopting practices to preserve natural resources.
How green is your city? How does it match up to other cities? Is it making progress in becoming more sustainable?
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.
Land, Energy, Water
The ecological footprint measures how much land and water area a city requires to produce the resources it consumes and to absorb its wastes.
Ecological footprint is measured in global hectares (gha) per capita. The global average is around 2.6. The footprint of London UK, for example, was measured at 4.5, slightly lower than the UK average of 4.6. More people in London use public transport than almost any other city in the UK, 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.
Another measure is a city’s carbon footprint, which is the total amount of greenhouse gases it produces. The basic unit is kg or ton of CO2. The global average is 1.19 metric tons per person. 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.
