c40 cities emissions man on bike with mask
How are these emissions measured? And do they really correspond to the activities of these cities' inhabitants? Photo: Kevin Grieve on

Twenty seven cities, including Melbourne and Sydney, have reached peak greenhouse gas emissions according to the C40 Cities website last week. So how come their emissions are still rising?

Do you live in any of the following cities? Barcelona, Basel, Berlin, Boston, Chicago, Copenhagen, Heidelberg, London, Los Angeles, Madrid, Melbourne, Milan, Montréal, New Orleans, New York City, Oslo, Paris, Philadelphia, Portland, Rome, San Francisco, Stockholm, Sydney, Toronto, Vancouver, Warsaw or Washington D.C.

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These cities are members of C40 and if you live in any of them you might feel you want to give yourself a pat on the back. Congratulations, you don’t have to feel guilty any more about contributing to global warming. Because C40 Cities – which supports city leaders in reducing greenhouse gas emissions and becoming more sustainable – is saying that their emissions are now going down.

But hang on – what does this actually mean? How are these emissions measured? And do they really correspond to the activities of these cities’ inhabitants?

The C40 Cities post, and the meant-to-be-shared video accompanying it, reference a report that contains projections (Deadline 2020) but provides no hard sources to back up the claims for each city.

But buried in a footnote to the blog is a link to another website, also run by C40, which details the methodology behind the calculations.

Production-based emissions

There are two different ways of measuring a city’s greenhouse gas emissions: you can look at the quantity of the emissions it produces, or the quantity of emissions that results from everything that’s consumed in the city.

The methodology behind C40’s claim is the former: in other words, it adds up all of the emissions from different sectors: energy and manufacturing, buildings, transport, waste, industrial processes, agriculture, forestry and other land-use, and emissions due to leaks. (It’s called the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories: An Accounting and Reporting Standard for Cities, or GPC for short.)

Sources and boundaries of sector-based city GHG emissions in the GPC.

One striking thing stands out from the list of cities: they are all in developed countries. Given that most developed country cities – including those in the above list – are not highly industrial, and that heavy industry is responsible for a large proportion (about 35 per cent) of total greenhouse gas emissions around the world, then it becomes less surprising that they are producing fewer emissions.

Cities tend to evolve, such that in their infancy they are built around heavy industry, coal burning, and other polluting activities. As they, or their host countries, become richer, these tend to close down, to be replaced by secondary manufacturing and service industries, which tend to use less energy and are less polluting.

However, their residents need plenty of infrastructure and energy, so they continue to consume the products of heavy industries. Only now these are imported.

The most heavily polluted cities in the world tend to be in the youngest and fastest growing economies: China, Southeast Asia, India. They are fast growing cities too, because they are exporting a lot of products to richer countries and attract workers.

All of the above cities are comparatively well off, with the possible exception of New Orleans, which may be included simply because much of its infrastructure was destroyed by Hurricane Katrina in 2005.

Consumption-based emissions

If, by contrast, you look at the consumption-based greenhouse gas emissions of cities, which C40 itself has done in a report co-authored by the IPCC and the University of New South Wales, you find that, on average, emissions prove to be 60 per cent higher than when calculated using production method. And they are going up, not down.

Caption: Summary of the sector-based GHG emissions and consumption-based GHG emissions for 79 C40 cities

This is because mature cities rely heavily on the supply of goods and services from outside their physical boundaries. The richer the city, the more it consumes. Globalisation has resulted in goods often being transported thousands of kilometres away to their customers (with consequences that would seem absurd to an observer from space; many countries export and import the same commodities. For example, France in 2016 imported just over $12bn of medicaments and exported $15.7bn of the same. It also exported just over half the value of petroleum oils that it imported.)

As we’ve reported before, the vast majority – 80 per cent (63 out of 79) – of C40’s member cities have larger consumption-based GHG emissions than sector-based production GHG emissions. Only for 16 cities – mostly in South and West Asia, Southeast Asia and Africa – is the reverse true, which is what you would expect because they consume less per inhabitant (average wages are low) and are highly industrialised.

[insert consumption-based-GPC_emissions.png. Caption: Relative differences between consumption-based GHG inventories and sector-based greenhouse gas inventories for 79 C40 cities. A positive difference above the line indicates higher consumption-based GHG emissions than sector-based GHG emissions. A negative difference below the line indicates higher sector-based GHG emissions than consumption-based GHG emissions.]

Another study, published in the Scientific American this summer, corroborates this. It also used consumption-based analysis – this time comparing 13,000 cities. It found that most of the cities in the above list have high emissions in the world… with the addition of China’s large industrial cities, which make the things that everybody else buys.

The study uses income as a proxy for emissions. It finds that carbon footprints are highly concentrated. Just 100 cities drive 18 per cent of global emissions. For example London, Manchester and Birmingham combined contribute more than 20 per cent of the entire UK’s output; and Chicago, New York and Los Angeles combine to account for nearly 10 per cent of the USA’s overall footprint.

The website ranks the full 13,000 cities. Here are its top 27 emitters:

  1. Guangzhou
  2. New York
  3. Hong Kong
  4. Los Angeles
  5. Shanghai
  6. Singapore
  7. Chicago
  8. Tokyo/Yokohama
  9. Riyadh
  10. Dubai
  11. Wuxi
  12. Johannesburg
  13. Tehran
  14. Moscow
  15. London
  16. Benha
  17. Beijing
  18. Jakarta
  19. Al-Ahmadi
  20. Miami
  21. Samut Prakan
  22. Paris
  23. Dallas
  24. Tianjin
  25. Istanbul
  26. Detroit
  27. Philadelphia

Five cities are in both this list of high consumption-based emitters and the C40’s list of production-based post-peak emitters:

  • Chicago
  • London
  • Los Angeles
  • New York City

So, let those cities be not so smug about producing fewer emissions.

What should city leaders do? The Scientific American article’s researchers recommend that state and local governments wanting to reduce emissions can benefit by better understanding the distribution and drivers of footprints to understand their hotspots of consumption and production emissions, to “isolate carbon intensive nodes”.

The C40/IPCC consumption-based emissions report recommends that leaders in cities in these regions use consumption-based greenhouse gas inventories and their sector-based greenhouse gas inventories to help them better consider how to reduce overall emissions.

Why has C40 claimed 27 cities have peaked?

C40 has not responded to enquiries about this question, but you can’t blame it for wanting to put a brave face on things. They are trying to make cities feel good about themselves – encouraged. They want cities to believe they can increase populations and carry on as usual without feeling too disheartened about their efforts to reduce their impacts on climate.

The Deadline 2020 study overlooks consumption-based emissions (sometimes called ‘Scope 3? emissions) on the grounds that double accounting might occur if it used both production and consumption based models.

But consumption-based models are more intuitively linked to the idea that cities’ actions can reduce emissions. After all, cities cannot control the emissions associated with the production of imported goods; all they can do is choose not to import them.

Yet this would make no difference to their production-based emissions and therefore not affect their ranking in that league. So they can actually carry on supporting high-consumption lifestyles while at the same time seeming to claim that they are reducing their production of emissions.

This is a dangerous path that leads to complacency. In fact it is almost deliberately misleading. It is without doubt excessive consumption that is making the climate, and our environment in general, less able to support universal sustainable lifestyles.

But C40’s President is Michael Bloomberg, who is worth 51.8 billion dollars, the 8th-richest person in the United States, and the 11th richest person in the world – a one-man carbon footprint hotpot. Can you really expect such a person to tell others to consume less?!

The consumption-based emissions report‘s co-author, Michael Doust, who is himself the programme director for C40 Cities, says: “We’re missing the other side of the coin if we only measure emissions involved in the production of food, energy, or other products and services. Knowing what the consumption emissions are and where allows cities and residents to make better decisions on how to reduce their carbon emissions.”

So what we’re seeing is that wealthy cities like London, Paris, New York, Toronto, Sydney and Melbourne, that no longer have large industrial sectors, can claim to have significantly reduced their local emissions. But their actual emissions have risen substantially, with their citizens’ personal carbon footprints larger than most people’s in the world because of their high levels of consumption.

Only a consumption-based approach can capture direct and lifecycle emissions of goods and services (including those from raw materials, manufacture, distribution, retail and disposal) as it allocates greenhouse gas emissions to the final consumers of those goods and services, rather than to the original producers of those GHG emissions.

It’s this kind of realism, rather than C40’s over-enthusiastic cheerleading, which I believe is going to save the planet, if anything can.

David Thorpe is the author of The One Planet Life, about living within planetary boundaries, Passive Solar Architecture Pocket Reference and Solar Energy Pocket Reference. 

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  1. Agree, this is a very useful article. While we are on the topic of carbon accounting; why do we focus so much on annual emissions ? It’s the accumulated emissions, year on year on year that impact the environment. Taking a balance sheet approach to carbon accounting would highlight the urgency required and would temper some of the celebrations that accompany actions that accompany small annual reductions. It might even have more governments and businesses considering what remediation options are available. (move to doing good rather than just less bad)

  2. Good article thanks David and 5th estate. Of course we should be measuring consumption based emissions and using the same measurement method universally and that’s a complex problem. All of the methods are riddled with cheating of various kinds between nations, regions industry sectors and even practitioners. We also get a very different story if we measure totals or per-capita. Sydney isn’t highlighted, because the article focusses on totals but if it looked per-capita it would be one of the worst emitters.