The hunt for the world's most sustainable cities

---

How do you reduce a city to a score? It’s hard enough for judges when ranking freestyle snowboarders or the best takeout Thai food. With cities, the task is inherently more complex, but it’s pressingly relevant to try since more than half of humanity depends on a city for health, safety and prosperity. And the UN projects that more than two-thirds of us will live in cities by 2050, the same year we need to achieve net-zero.

I’ve attended the Federation of Canadian Municipalities conference on sustainable communities for more than a decade, first as a city councillor, then as mayor, and now as an advisor on climate investing and community resilience. After years of relentless focus on climate change mitigation through decarbonization, creating resilience to the changes that are already upon us took centre stage at this year’s conference. This was also true at the COP27 climate summit in Egypt in November, where a central thrust was negotiating what’s called loss-and-damage funding for the Global South based on the devastating impacts of historic emissions from the Global North on many of the world’s poorest cities.

This might be the last stage of grief (acceptance) or the first step in acknowledging the true scale of the problem.

This is not to say for a minute that we should relent on decarbonization – far from it. If anything, the devastating floods in Pakistan and California over the last year should amplify our resolve to hold warming to the minimum possible scope of devastation while simultaneously increasing resilience to those rising risks, whatever their final apex.

This is the point, and it’s a relentless but critical one: we need to address all facets of resilience and sustainability in parallel. We don’t just have to build the plane while we’re flying it; we have to learn to soft-land it too – an inherently interrelated and complex set of tasks.

Indeed, cities are arguably the most complex systems humans have yet engineered for ourselves. The vast networks of hard infrastructure alone are boggling if you stop to think about them, much less the extraordinary diversity of human activity found in the hive of structures, streets and open spaces. Add in the watersheds, airsheds and ecosystems that many forget are under, around and throughout our cities, and the beautiful complexity of urban systems begins to resolve.

While each city has its unique context, history, geography and culture, there are some features that are more easily comparable, such as water use and air quality. These hard factors are so important to our index that having the best score on particulate air pollution in the entire Corporate Knights database launched Winnipeg into top position among Canadian cities and ninth overall. A strong showing for the city’s first year included in the index.

However we measure sustainability, some cities tend to come out consistently at the top based on all-around excellence. Despite adding 20 more cities to the 2023 Sustainable Cities Index, the top five cities did not change position from the 2022 ranking: Stockholm, Oslo, Copenhagen, Lahti and London, indicating strong consistency in their performance and robustness in the ranking methodology.

The three Scandinavian cities at the top each take best in show in at least one sustainability KPI (key performance indicator). Stockholm ranks highest on Scope 1 greenhouse gas (GHG) emissions thanks to longstanding decarbonization policies, extensive public transit and a strong tradition of well-built buildings fed from co-generating district energy systems. The Swedish capital also received top scores on open public space, the lowest automobile dependence and best solid waste avoidance in the index.

READ MORE: These circular cities want to send landfills to the trash bin of history

Oslo ranks highest on climate resilience for its green roofs and climate-anticipatory stormwater strategies while also maintaining the best water access among all ranked cities, as well as strong electrification progress, from cars to construction. Copenhagen, meanwhile, has the strongest results on water consumption. It is worth asking ourselves what is in that proverbial water in these Nordic communities that engenders such a strong commitment to systems-level approaches to sustainability and how can the rest of us emulate it?

In addition to the hard measures of emissions and the data about transportation systems, we can also test for an appreciation of complexity by looking at cities’ sustainability policies. Sydney, Australia (seventh place), or example, engaged very actively in the survey this year and was able to move up 19 positions from its rank last year by showing it has robust sustainability policies, coming up right below Oceania leader Auckland (sixth), with their best-in-region climate adaptation and resilience policies.

Correspondingly, cities with poor policy showings had weak results in other output categories and thus on overall scores. Karachi, Pakistan (70th), and Mumbai, India (65th), score zero on the sustainability policy framework and also have serious GHG, air-quality and water-access challenges.

Do policies shift outcomes, or is it easier to make bold policy if you already run on hydro power instead of legacy coal? Either way, cities must nurture policy sophistication (both on decarbonization pathways and adaptation to weirder, wilder and wetter weather) to drive material improvements in sustainability.

Network initiatives like C40 Cities strive to bring Global North and Global South cities together to build capacity and solutions that work in different contexts while holding each other accountable to deliver through consistent public reporting. But most of the world lives in the hundreds of smaller cities, communities that aren’t necessarily at those prominent tables, or included in this index. Nevertheless, we need all our cities to aim higher, especially the fast-growing megacities in the bottom half of our rankings.

One might reasonably ask whether it is fair or even just to evaluate all cities to the same standard, when some are still recovering from colonial exploitation, or imposed austerity policies, and even war. Or whether it is comparable to juxtapose cities with massive informal settlements like São Paulo, Brazil (55th), with top-ranked San Francisco (21st), where almost nobody can afford to live.

One related challenge is reconciling the interplay of social and economic inequality with environmental outcomes. Which is why this year the analytics team developed the Corporate Knights Socio-Economic Adjustment Factor to adjust environmental performance indicators where they coincide with unsustainable social and economic conditions.

As our research analyst Nadia Morson notes, “Indicators such as per capita greenhouse gas emissions or per capita water consumption will be low in wealthier cities if water conservation and efficiency are priorities, but they will also be low in lower-income cities due to poverty and limited access to fuels, electricity and potable water.” Megacities of poverty may have a lower per capita carbon footprint but are problematic in a different way than wealthy cities with specific sustainability blind spots because of mass human suffering and lower inherent resiliency to rising perils. The adjustment is meant to account for that by considering a blend of income inequality, per capita GDP and human development index scores.

In a dominantly urban age, with deep social and environmental challenges facing all species, including us, how and whether our cities attain sustainability may make all the difference for our future. So while cities are inherently difficult to compare, it is worth lifting up high achievers and considering what may be required to better support those that are lagging behind.

Don Iveson advises a number of NGOs as well as cleantech, insurance and social impact businesses. He was mayor of Edmonton from 2013 to 2021.

This year we have organized the ranking by region. Click on each region below so see which cities scored A, B, C, D or F.

INDICATORS

The 2023 Sustainable Cities Index is composed of 12 quantitative indicators of environmental sustainability performance. The method is simple: for each of the indicators, the necessary data points are collected, either from public data sources or directly from the cities themselves, through our interactive data hub.

Values for each of the 12 indicators are converted to a score out of 1.0. Based on the scores of each indicator, each city will receive a letter grade and rank for their overall score on the index. Detailed scoring method is available in the full methodology document.

Indicator	Method	Weight
Scope 1 GHG emissions per capita	Divide the city’s sector-based inventory of Scope 1 emissions by the city’s population. This indicator reflects fossil fuel consumption in the city.	10%
Consumption-based Emissions per capita	Divide the city’s consumption based GHG emissions inventory by the city's population. Corporate Knights developed a simplified method for estimating a city’s consumption-based inventory, described below. Cities’ GHG footprints typically far exceed the emissions included in their direct, sector-based inventories, and this indicator captures that aspect of urban sustainability.	10%
Air Quality	Micrograms of fine particulates (less than 2.5 μm diameter) per cubic metre of air, a standard indicator of air quality.	20%
Open Public Space	Divide city area for public parks, recreation areas, greenways, and other areas accessible to the public by total city area.	5%
Sustainable Transport Mode Share	Divide number of trips by sustainable modes (walking, cycling, or public transit) by the total of all trips.	5%
Automobile Dependence	Divide number of registered road vehicles by number of households.	5%
Road Infrastructure Efficiency	Divide the length of the road network in kilometres by square kilometres of city area.	5%
Water Consumption	The average amount of water consumed in litres per capita per day.	5%
Potable Water Access	The percentage of city population with access to potable water.	5%
Solid Waste Generated	Divide the amount of municipal solid waste generated in tonnes per year by the city population.	10%
Climate Change Resilience	Divide the national Notre Dame GAIN Readiness Score by the Notre Dame GAIN Vulnerability Score. A higher ratio indicates a high level of readiness for climate disasters and/or a low level of vulnerability to climate disasters.	10%
Renewable Energy Policy	Starting with an assessment of the number of key policies tracked by REN21 that the city has enacted: (i) renewable energy target, (ii) electric vehicle target, (iii) emission reduction target, (iv) net-zero GHG target, and (v) renewable energy enabling policy. Amended with additional information to support renewable energy policies and targets as provided by cities.	10%