The Big Picture Approach to Cities and Climate Change

It was former London Mayor Ken Livingstone who started the ball rolling in 2007 when he announced that “Urban areas are responsible for over 75 per cent of greenhouse gas emissions, so the battle to prevent catastrophic climate change will be won or lost in cities.”

That figure – “75%” – became the urban climate factoid of the decade.  It spread like a virus popping up again and again in newspapers, mayor's speeches, and government reports. The thing was, no one knew quite where it came from. What was the math behind the meme? Was Climate Change all cities' fault – or were they going to be the new climate heros?

A year later the number got some closer scrutiny (see here) and last month a new paper (.pdf)came out that does an excellent job of sorting out how to understand cities' responsibilities and what they can do about them.

The paper, by the World Bank's lead urban specialist Daniel Hoornweg, delves into the difficulties of counting urban emissions. For every greenhouse gas molecule released directly in a city (say from a car's tailpipe, or a local factory) others are released making the energy, food, and commodities consumed by urban populations. If you don't count consumption related emissions, then the high estimates of ghg emissions don't make any sense. Instead of 75% you end up closer to 30%. So which figure is right?

Hornweg and his co-authors Lorraine Sugar and Claudia Lorena Trejos Gomez, argue for the big numbers and call for an international standard for urban ghg inventories that takes into account both consumption and production based emissions. Their point is an excellent one: even if these emissions take place outside of cities, urban policies are in a position to do something about them.

Cities are more politically nimble than national governments, more able to demonstrate the the multiple benefits of climate policy for overall quality of life, more able to cooperate with each other and their citizens, and have their hands on policy levers that can have large global impacts.

But crucially – I think – if cities are going to talk the talk, then they have to walk the walk.  Organizations like the C40 have used the 75% figure to carve out a space for cities on the international stage, but so far their programs fall short of addressing the truly holistic approach to climate policy that these figures represent. Leading cities like Portland, Vancouver, and Denver have begun adopting targets for upstream emissions linked to things like building materials and food supply.

Now that inclusive inventories of urban impacts are part of our collective consciousness, it's time that policies to address them went viral as well.

[See here for most on why we need to think big about urban emissions. image: Vincent Laforet]

Below are a few excerpts from the article, which has excellent data on the wildly different emissions from cities around the world, as well as the striking differences that can occur within cities themselves. It also contains a good summary of a variety of urban climate policies and tools.

From "Cities and greenhouse gas emissions: moving forward"

While data can be difficult to obtain, the reporting of upstream, consumption-based emissions provides the most comprehensive view of the greenhouse gas emissions arising from an urban system for decision makers. Upstream emissions may be used to inform systemic consequences of climate change actions. Some actions that reduce climate change in cities may increase emissions in rural areas; for example, exporting cement manufacturing to rural areas removes emissions from cities but increases emissions associated with transportation. The Scope 3 analysis of Denver led to the adoption of green concrete policies, reducing upstream emissions in new construction projects. As cities create strategic plans for mitigation, it is important to consider these upstream impacts as they can provide indications of what is driving emissions.

The city of Toronto, for which some of the most comprehensive spatial data is now available, provides an important observation: in the total emissions per capita value for citywide (9.5 tCO2e) and metropolitan (11.6 tCO2e), residential contributions account for approximately 68 per cent and 57 per cent, respectively. The “low” and “high” neighbourhoods vary by as much as a factor of 10. This suggests that what you buy is important, but what type of housing and neighbourhood you live in is much more important.

Cities and countries that enacted complementary policies for waste management practices have had the most success at solid waste diversion, for example: local tipping fees; bans on products and materials, such as limiting packaging materials and banning organics from landfill; extended product responsibility; and clearly articulated local and national waste diversion targets.

Reducing GHG emissions will be achieved through a similar suite of policies and actions, for example: local “emitting” fees and emissions trading systems such as there are now in place in Tokyo; local and national targets; extended product responsibility; and local
provision of practical alternatives such as improved public transport, more energy-efficient homes and more low-carbon city forms. With both GHG emissions and solid waste, the disparities within and across cities are striking; the poor generate little but are often severely impacted.


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This is a blog for news and views on the future of sustainable cites. A major revamp is in the works. Until then I am keeping this version up as an archive of my past writing.

You can expect occasional updates, but not with the same frequency as in the past.

You can also find my writing on urban redesign and sustainability in ReNew Canada, The Mark, Sustainable Cities Canada, WorldChanging, and other more specialized academic publications.

Info on my consulting work, c.v. and current research focus is all here.