Calculating a City's Carbon Footprint

Half of the world’s population nowlives in cities, but determining how much each of those places contributes to the accumulation of greenhouse gases that cause global warming is no easy task. And if cities do not know what their carbon footprint is, they can’t reduce it effectively.Hence the importance of a study conducted by a teamof scientists from several countries, which uses a common methodology to compare the emissions of 10 major cities.

For the first time, the entire life cycle has been analyzed, though there are still gaps to be filled. The study, published in Environmental Science and Technology magazine, found that Barcelona emits the least per capita, six times less than Denver, the biggest polluter. In between, from less to more, are Geneva, Prague, Lon- don, New York, Bangkok, Cape Town, Toronto and Los Angeles. Including the entire life cycle means that in addition to direct emissions those used to make, for instance, the fuel used to generate heat are also calculated. “We’ve come in last in this ranking, but emissions are increasing, especially due to the use of air conditioning. We can’t rest on our laurels,” says Gara Villalba, the scientist who analyzed Barcelona.

Some factors that have influenced the Catalan capital’s good score are its warm climate, the fact that a significant portion (15 percent) of the energy it consumes is nuclear- generated and that it has a high population density. Some of these corresponding factors work against Denver, which has a very extreme climate, a very low population density and many single-family homes with little insulation. Geneva does very well, because almost all of the electricity it consumes comes from hydroelectric plants; it even exports this type of electricity. Toronto, on the other hand, uses a lot of coal; so does Prague.

Transportation is another key factor. Thus, the cities in the United States performbadly due to heavy reliance on cars. In Denver this form of transportation represents 92 percent of the total, whereas in Europe, Geneva comes in at 55 percent, and Lon- don at 49 percent. These percentages are indicative of the quality of public transportation, urban planning and environmental policy, argue the study’s authors, who have taken into account seven components of the urban inventory: electricity, heating and industrial fuels, industrial processes, ground transportation, aviation, marine traffic and waste. “In Barcelona, we’ve only calculated the complete life cycle for fuel,” explains Villalba, due to a lack of data on natural gas. Nor did they have enough information to deter- mine the total impact of waste and construction material. The scientists are now working to calculate emissions associated with the activities in Barcelona’s port. When it comes to calculating its carbon footprint, the Catalan capital is way ahead of Madrid, where practically no studies on this subject have been published. Barcelona’s leaders also plan to reduce emissions by building two 425-megawatt combined cycle plants in its port.


El Pais - Internatioonal Edition - Monday October 12th

For full article see:

Environmental Science and Technology 2009
Greenhouse Gas Emissions from Global Cities

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