Internet Explorer 11 is not supported

For optimal browsing, we recommend Chrome, Firefox or Safari browsers.

Cities Try to Measure Greenhouse-Gas Emissions Better

There are two forward leaps in how cities track pollution. One new effort aims to harmonize the many methods cities use for tracking their greenhouse-gas emissions. Meanwhile, London is looking to push the whole field of city emissions tracking to a new level.

Shutterstock/ Taiga
By Christopher Swope

By now, big-city pledges to cut greenhouse-gas emissions have a familiar ring to them. Seoul says it will reduce emissions 40 percent by 2030. Amsterdam pledges to cut emissions 75 percent by 2040. Seattle aims to eliminate all emissions by 2050.

But there’s a big problem with all these pledges: Cities use all kinds of different methods of measuring and reporting their emissions. While each accounting makes sense in its local context, it’s difficult to compare cities with each other. It’s also hard to roll up meaningful assessments of the overall contribution cities are making to combat climate change.

That will begin to change next month. A new global standard is coming that will give cities a common framework for measuring and reporting their emissions. The details are to be announced December 8 at the United Nations Climate Change Conference in Lima.

The new standard has a clunky name: the Global Protocol for Community-Scale Greenhouse Gas Emissions, or GPC. But its launch could be a transformative moment in the fight against climate change.​

The reason is straightforward. When it comes to greenhouse gases, cities are both the problem and the solution. Some 54 percent of the world’s population lives in urban areas, and these cities are estimated to generate 70 percent of the world’s emissions. As political actors, cities have often been more aggressive than national governments — not only at pledging to cut emissions but also at backing up those pledges with actions. Proponents of the new standard hope it will encourage more and more cities to take such carbon-saving steps as improving energy efficiency, discouraging auto use and reducing waste sent to landfills.

“It’s taken 15 years to come up with an approach that everyone agrees to,” says Dan Hoornweg, a professor at the University of Ontario Institute of Technology and former World Bank official who has studied city emissions inventories in depth for many years. “Now that we have it, we can stop debating and start doing.”  

Many existing methods

Measuring emissions is a complex science. The calculations are even more challenging at the geographic scale of a city than across a whole country.

For example, city-scale measurements are complicated by the question of how to treat “transboundary” emissions from, say, car trips that start in one city and end in another. Different cities have taken different approaches to counting these trips.

They’ve also differed in terms of which greenhouse gases to count — some count all six of them, while others focus solely on carbon dioxide or methane. Then there’s the question of what emission sources get counted. Some cities count just emissions from transport or buildings, while others add emissions from industrial processes or waste, for example.

These are the sorts of questions the GPC aims to resolve by getting cities on the same page about what they are tracking and how to report the data. It was developed by the World Resources Institute, the C40 Cities Climate Leadership Group and ICLEI - Local Governments for Sustainability.The effort is linked to the broader quest to harmonize global data on city performance. For example, a new international standard for data on cities, known as ISO 37120, incorporates the GPC as its indicator for greenhouse-gas emissions.

Some 35 cities pilot-tested a preliminary draft of the GPC last year, and about 70 are now using an updated version of that. What will be published next month is a finalized rewrite of the protocol, ready for wide-scale adoption by cities around the world. The organizations behind the GPC plan to ramp up training and technical assistance for cities next year as more cities adopt it.

One pathway to scaling this up will be through the C40 Cities group, which now has 69 members as well as a network of cities working specifically on emissions measurement and reporting. According to Michael Doust, C40’s head of measurement and planning, a number of the organization’s members don’t yet have an emissions inventory. “It’s the first step,” Doust says. “If you don’t know where your emissions are coming from, it’s hard to develop an evidence-based action plan.”

Cities that already have inventories will find the GPC useful too, says Wee Kean Fong, a senior associate with the World Resources Institute in Beijing. Having comparable data at last will help mayors and other city leaders benchmark their climate efforts against other cities, he says. “If cities do not comprehensively account for all the emissions, if they miss certain sources, then they will miss opportunities to reduce.”

London’s leap

As the global standard takes hold, the city of London is leading a parallel effort to push the whole field of city emissions measurement in a complementary but innovative new direction.

London was one of the first cities to begin comprehensively measuring its greenhouse-gas emissions back in 2004. As with most cities — and as with the GPC — London’s initial efforts focused on direct emissions that clearly originate from households or businesses located within the city’s borders. It also included emissions from power plants that might be located outside city limits but serve customers based in London.

Now, London is pushing beyond these so-called “Scope 1” and “Scope 2” emissions. The city has begun tracking the more nebulous but critical subset of emissions known as “Scope 3.” These include a wide range of indirect emissions that technically occur outside London’s borders — either within the metro region or beyond it. But these emissions are only occurring because of activity within the city.

The examples are practically endless. Emissions from a TV purchased in London but manufactured in China are counted. Food production and shipping is a big factor, since London produces relatively little of its own food. The same is true for concrete imported to construct buildings in London. Transport of people and goods across city borders is included here, including aviation. As Matthew Pencharz, a senior adviser to Mayor Boris Johnson on environment and energy puts it, “It’s a growing trend to think about what the entire impact is of a city activity.”

Bigger footprints

London used two different methods of measuring these indirect emissions. One involves a meticulous look at the supply chains behind products and services consumed in London. The other takes a broader look at what is consumed in London, regardless of where it is produced.

Both methods produced much bigger carbon footprints for London than had previously been calculated. It came out twice as large under the supply-chain method; it was nearly three times as big under the consumption model.

What should London do with this data? That’s always the next question after a city finishes an emissions inventory. London officials aren’t sure yet, although they’re clearly paying attention to how the analysis laid bare the problem of emissions related to food. In London’s previous measurements, food barely registered at all as an emissions problem. In the new ones, food accounts for more than 10 million metric tons of CO2 equivalent — a significant share of London’s overall emissions.

“If you can’t measure something, then it’s impossible to manage it,” says Pencharz. “We obviously all knew that making food and shipping it to London created a lot of emissions. But we didn’t know at a data or organizational level how much that really is. In order to work out interventions to address that, you have to measure it in the first place. You need somewhere to start from.”

London recently won a climate leadership award from C40 and Siemens for its emissions accounting regime. The city’s methods — which are in sync with the GPC protocol but clearly go well beyond it — have been codified into a British national standard known as PAS 2070. London also published a case study showing step-by-step how it applied the methodologies to different numbers. All of which is aimed at making it easy for other cities to follow London’s lead.

As the GPC protocol evolves, it also may push into measuring indirect Scope 3 emissions, says Wee Kean Fong of the World Resources Institute. If that happens, it would represent a major push for cities to be thinking of environmental impacts beyond their borders — to their wider metro areas and to the rest of the world.

Dan Hoornweg thinks the spread of that kind of thinking is inevitable. “We now have the first quantifiable description of the responsibility that a citizen of London has for total greenhouse-gas emissions around the world,” he says. Hoornweg believes the idea that cities can measure their broader environmental impacts in this way will catch on beyond emissions. London-style measures of indirect impact can be translated to water, waste or biodiversity.

“This thing London did is the first installment of quantifying global citizenship,” he says. “Which is really cool.”


Citiscope is a nonprofit news outlet that covers innovations in cities around the world. More at
Special Projects