Image: Wikimedia Commons

When you’re in a major city, it can be easy to forget about the outside world. But city life is not a hermetic experience—in fact, the environmental footprints of cities can stretch around the world. A new study shows that cities are overlooking a major source of emissions as they craft policies to transition toward a cleaner, lower carbon future: those arising from goods and services that originate outside of the city, otherwise known as upstream emissions.

Published in Scientific Reports, the study found that these upstream emissions—which occur along global supply chains as products and services make their way to consumers in cities—are typically about equal in size to the total emissions coming from within a city’s borders. While this may sound like bad news, the authors, primarily based at the Potsdam Institute for Climate Impact Research in Germany, think it presents new opportunities for local policymakers keen to tackle climate change. In the U.S., this is especially relevant for cities feeling thwarted by Trump’s refusal to take climate change seriously.

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While things like iPhones and jeans, which are often shipped around the globe, might spring to mind as prime sources of upstream emissions, the study determined that housing and transport are actually the largest sources.

Upstream emissions from housing the generation of electricity, as well as remote heating, water supply, sewage and solid waste treatment. For transport, they include the production and maintenance of cars as well as the extraction, refining and transportation of gasoline, and emissions from private travel.

Housing and transport are sectors that city governments are well positioned to address and often keen to make more sustainable. Currently around 7,500 cities worldwide, representing nearly 700 million people, are signatories on the Global Covenant of Mayors for Climate & Energy, a commitment that includes emissions reductions targets.

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“The important point for city policymakers is that buildings and transport are responsible for the majority of local and upstream emissions of urban households,”the Potsdam Institute’s Peter-Paul Pichler told Earther. “This means that two thirds of the GHG footprint is caused in areas which are well within the reach of local policymaking.”

The report compared the emissions profiles of four major cities, New York, Berlin, Mexico City, and Delhi. It found that while each had large upstream emissions, those emissions varied in scope and origin. More than half of Germany’s upstream emissions occurred in other countries like Russia and China, while only 20 percent of Mexico City’s smaller upstream emissions came from outside of Mexico.

Across the four cities, an average of 28 percent of upstream emissions came from housing, 23 percent from transportation, 26 percent from food, and 24 percent from other sectors.

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Image: Scientific Reports

According to the authors, local decision-makers have been focusing primarily on “territorial emissions,” or direct emissions that originate within city limits, because they’re easier to address. According to the study, these include emissions from industry, commerce and public infrastructure services.

The authors hope this new report will both open urban leaders’ eyes to the potential carbon-cutting opportunity in upstream emissions, and also give them a tool to better understand the sources of their city’s emissions.

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When it comes to housing, the way cities source the cement and steel used in construction can make a huge difference in CO2 emissions. These materials typically require large amounts of fossil fuels to produce, and any low-carbon alternatives should be considered, according to the report. A similar thing can be said for transportation. Cities should try to procure power used to run public transportation from renewable sources whenever possible.

Pichler said that while cities being built now have the biggest opportunities to integrate low-carbon thinking into their planning, they are often financially restricted. After all, most of the fastest-growing cities are in emerging economies in the developing world.

“New ways of financing, maybe through international action, could be a way forward here,” he said.

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As for all the individuals living in city apartment buildings and riding the public transportation? They can also help reduce their city’s carbon footprint, by eating less meat, flying less, biking more, and making informed decisions.

“Choose a renewable power supplier if you have the choice, choose a bank which does not invest in the fossil fuels industry, look for good insulation when choosing a home,” said Pichler, listing just a few ways one can be proactive.