This index is an ongoing empirical study, updated and refined quarterly. Many of the cities studied are now approaching their data collection limits, which brings us to the next phase of development: identifying and collecting data that measures bio-capacity and human anthropogenic footprints in greater depth. This is an iterative process that requires collaboration with all levels of government, academia and industry. The goal is to create tools that give people greater visibility into human impact on the biosphere and identify areas where solutions can have substantial impacts.
All formulas and equations used are published at the bottom of this article and they are further defined in the downloadable spreadsheets in each city's detail webpage.
No new indicators were added and five indicators were revised. Many of the intermediate data calculations are now shown in the spreadsheets.
- Workforce Commuting Outside City is now calculated as the number of commuters
- Clean Electric Capacity now includes nuclear power as an emissions free power source
- Parkland Area Percentage was revised to a percentage of city area
- Natural Lands Percentage was revised to a percentage of city area
- Data Freshness is now scored