Reducing emissions in cities has a broader effect than expected

A new study has found that an urban population’s influence on greenhouse gas emissions outside of city limits are much more substantial than previously realized. The good news is that by narrowing down the primary source of a city’s emissions, including indirect emissions, policy makers will be able to make more informed decisions.

Experts from the Potsdam Institute for Climate Impact Research determined that purchases made by the urban population beyond the city’s territory are roughly equal in size to the emissions occurring within city limits. The researchers found that housing and transport cause most city emissions, locally and also upstream.

For their research, the experts calculated the first internationally comparable greenhouse gas footprints for Berlin, New York, Mexico City, and Delhi.

“It turns out that the same activities that cause most local emissions of urban households – housing and transport – are also responsible for the majority of upstream emissions elsewhere along the supply chain,” said lead-author Peter-Paul Pichler.

One example of outside emissions caused by the housing sector can be found in the cement and steel used to construct city buildings. Producing these materials requires an enormous amount of energy elsewhere. The use of low carbon construction materials could make a huge difference in decreasing a city’s indirect CO2 emissions.

With transit, expanding facilities and services could have a big impact on minimizing emissions by reducing local traffic. Additional public transit could also decrease emissions outside of city limits by reducing the number of cars that need to be built somewhere else. Furthermore, cities could use renewable sources of energy such as solar power or wind power to run subways and electric buses. This could have enough influence to actually close down far-away coal-fired power plants.

“People often think that mayors cannot do much about climate change since their power is restricted to city limits, but their actions can have far-reaching impacts,” explained Pichler.

While the greenhouse gas footprint in the four cities analyzed for the study ranged from 1.9 tons in Delhi to 10.6 tons in New York, the ratios of local to upstream emissions as well as the influence of the housing and transport sectors turned out to be roughly the same. Berlin’s indirect emissions had the farthest reach, with over half of the city’s upstream emissions occurring outside of Germany in Russia, China, and across the European Union.

“The power of cities, open interconnected systems of great density, to tackle climate change even in times of uncertainty on the national and international level has been underestimated by both many local decision-makers and most of the international community,” said senior author Helga Weisz. “Cities must be encouraged and enabled to focus on their full emission spectrum – local and upstream – as they continue to develop their climate mitigation plans.”

The research is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer