The world’s most sustainable cities might not be what you think

Last month the sustainability research group Corporate Knights published their Sustainable Cities Index. It celebrates the world’s most environmentally progressive cities, and you can probably guess some of the places that feature. Here’s the top ten:

1. Stockholm, Sweden
2. Oslo, Norway
3. Copenhagen, Denmark
4. Lahti, Finland
5. London, UK
6. Auckland, New Zealand
7. Sydney, Australia
8. Berlin, Germany
9. Winnipeg, Canada
10. Vancouver, Canada

Scandinavia does very well, and having visited some cities in the region for the first time last year, I can see why. Europe and Oceania are also well represented. Don’t miss the particularly glowing performance by Canada here. It doesn’t just get two into the top ten. If we were to carry on reading the index, we’d find seven in the top 20 – Canadian cities rock, basically.

This is fairly standard climate reporting, telling us what we already know: that advanced Western cities are the greenest.

However, there is some devilry in the details. Corporate Knights’ index is – like all indices – derived from a range of different datasets combined into a single score. In this case the index includes carbon emissions, water use, car dependency, green spaces, air pollution and several other measures. For each of these, figures are calculated, adjusted and weighted before they are compared and ranked. The full methodology is available, and there are two things I wanted to highlight.

First, Corporate Knights have included two different sets of data on carbon emissions. There is the direct, or sector-based, emissions. These are the ones produced in the city itself. Unusually and to their credit, they have also included consumption emissions – the emissions from all the stuff that is produced elsewhere for consumption in the city.

To illustrate the difference, here’s a helpful little diagram from Portland’s carbon accounting. You can ignore the numbers on it, Portland’s not one of the cities in the index. They’ve just done a good job presenting it and it’s the circles that are the important bit.

As the graph shows, there are emissions that occur in the city, from all the activities there – that’s the green bit in the middle. If the city has a lot of factories, then it is producing stuff that will be used somewhere else, and so some of its emissions should be taken off for exports. That’s the red bit, and more relevant in manufacturing economies in Asia. Then there are the emissions from all the stuff that’s produced and shipped into the city – food, materials, products, etc. That’s the consumption emissions bit, shown here as the big blue circle.

Cities don’t produce everything they need, so their consumption emissions will almost always outweigh the local ones. A pioneering ARUP study into this a couple of years ago found that 85% of a city’s emissions occur outside of its boundary.

Corporate Knights include consumption emissions in their index, but they weight it at 10% of the overall score – the same as direct emissions – even though it is far larger. The result of this is that there are cities with small local emissions that perform well, despite having a huge global footprint. Other places, where people consume far less, don’t see their low consumption reflected fairly in their overall score.

For example, Sydney appears here as one of the ten most sustainable cities on the planet. But it has consumption emissions of over 23 tonnes per person per year – that is 20 times the estimate of a fair share global footprint! All of Canada’s entries have carbon footprints over 16 tonnes per person. This is nowhere near sustainability, but the weighting of Corporate Knights’ index rinses consumer lifestyles of their global impact.

By contrast, there are several African cities that have per capita emissions well within that global share – Lagos at 1.7 tonnes, Nairobi at 1.8. If the full impact of cities on the climate were accounted for, a lot of places in the global north would tumble down the rankings, and some in the global south would rise.

There’s a second reason why the global south is under-represented in the Sustainable Cities Index. Corporate Knights have used a little tweak of their own inventing called the Corporate Knights Socio-Economic Adjustment Factor. This is used to account for the fact that not every low score is a sign of success. For example, you might score very low on water use because people don’t have access to running water – hardly a success story. In itself this isn’t a bad idea, but in its construction their adjustment factor includes the UN’s Human Development Index, which in turn uses GDP purchasing power. I don’t want to get too technical, but the end result is this: some countries are ‘adjusted’ downwards because they are poor.

Looking at adjusted scores, Norway’s cities are multiplied by 0.99 – they’re getting very close to their whole score. In the US it’s 0.95, a minor discount due to high inequality rates. South African cities on the other hand see their scores discounted by a third, and in Pakistan they are halved. Tanzania’s adjustment is 0.37. I can see what Corporate Knights are trying to do, but they have devised an index in which poorer cities cannot win.

As I say, Corporate Knights are attempting something very difficult, with data that is relatively newly available. I’m not trying to do a take-down of their index, and I’m not a statistician. What I think is worth highlighting is that we all bring a set of values, biases and assumptions to our work. CK have done this with their index, based on their own location and experience. That view of the world, as is often the case, obscures and devalues the performance of others in poorer countries.

Out of interest, take a guess at where Corporate Knights are based.

That’s right, it’s Canada.

So where are the world’s most sustainable cities? I don’t know, and I wouldn’t look to the Sustainable Cities Index for a definitive answer – it’s one way of answering the question, and other methodologies might get us closer. One thing is for sure – if we were all to emulate the lifestyles of those in the top performing cities in the Index, the world would be guaranteed to tip into irreversible and catastrophic climate change. And that doesn’t seem like a ringing endorsement of its rankings.

Personally, I think the most promising places for study might be those high or middle-income cities with low consumption emissions. Taipei is a good example – it’s a modern and advanced city, but citizens have just 10% of Sydney’s vast consumption emissions. It mainly scores low because of air pollution and green space. Similarly, South America’s cities – such as Medellin, Bogota or Curitiba – are all ones to watch.