Hong Kong is ranked the 8th most sustainable city.

The first question I ask myself when I see lists of "the most sustainable cities in the world" is: what are the criteria used?

The multinational construction firm Arcadis has produced its own list, out of a sample list of 50 cities from 31 countries around the world, but before we look at it, let's examine the criteria it has employed so we know what we are talking about.

It claims to be using the United Nations definition of sustainability: "development that meets the needs of the present without compromising the ability of future generations to meet their own needs". In applying this to cities it has looked at:

1. transport systems that enable people to navigate quickly and affordably;
2. clean and safe water supplies;
3. strong social structures and institutions;
4. a healthy and well educated workforce;
5. an environment conducive to strong economic performance;
6. performance on waste management;
7. performance on air and water pollution;
8. greenhouse class emissions;
9. resilience to extreme natural events.

Strikingly absent from this list are:

1. action on energy use;
2. improving biodiversity;
3. reducing inclusivity and inequality.

Nevertheless it could be argued that these three aspects might be included in the other indicators.

The second question I ask myself is: what are the sources of the data?

In this case, Arcadis says the data comes from: "United Nations, the World Bank, the World Health Organization, the International Labor Organization and many others". There is a full list at the end of the report.

The third question is: were all cities treated equally?

The 50 cities selected are intended to represent "an overview of the planet's cities", "wide-ranging geographical coverage" and "a variety of levels of economic development, expectations of future growth and an assortment of sustainability challenges". So it must be true that there may be cities that are more sustainable but which were not included in the initial sample list.

Three broad categories were deployed:

1. people (social performance and quality-of-life);
2. planet (environmental factors including greenhouse gas emissions);
3. profit (business environment and economic performance).

One may question the relevance of the last category to sustainability on the basis that some challenge the notion that the growth is compatible with sustainable development. On the other hand, profit is required in order to invest in sustainable development. It all depends on what happens to the profit.

No city has been able to achieve top ratings for all criteria. But it is a great surprise to find that at the top of the list are Frankfurt and London, with our old friend Copenhagen only coming third, and Madrid fourth.

While Frankfurt scores low on energy use and renewables, it scores highly on solid waste management and drinking water and sanitation, not to mention resilience to natural catastrophes, although some of this may purely be due to its geographical location.

In general, European cities perform well with German cities featuring strongly. The full list is:

The report also lists cities according to growth rate. The top 10 fastest-growing cities are:

These are the cities which will face the most challenges in the future. According to the report's writers, they need to look at their best performing peers and form strategic, global plans based upon their most vulnerable areas.

Whilst this report is interesting, there are others out there that are more so, being more comprehensive and more geared to a genuine definition of sustainability.

In general, one should treat with caution reports like this which come from companies that, however noble their intentions, ultimately produce them in order to draw attention to themselves and solicit more business.