= The Ecological Footprint is a data-driven metric that tells us how close we are to the goal of sustainable living. Footprint accounts work like bank statements, documenting whether we are living within our ecological budget or consuming nature’s resources faster than the planet can renew them. 
"‘For the management of renewable resources there are two obvious principles of sustainable development. First that harvest rates should equal regeneration rates (sustained yields). Second that waste emission rates should equal the natural assimilative capacities of the ecosystems into which the wastes are emitted. Regenerative and assimilative capacities must be treated as natural capital, and failure to maintain these capacities must be treated as capital consumption, and therefore not sustainable.’"
- Mathis Wackernagel 
"Building on human carrying capacity debate in the early 1990s, Mathis Wackernagel and William Rees introduced a new environmental accounting method, the Ecological Footprint, to measure human demand on the biosphere. After the 1992 Earth Summit in Rio the need to reduce human impact on the Earth became undeniable and widely recognized. What Wackernagel and Rees proposed was a method capable of making global ecological limits accessible by comparing human demand on the biosphere to its regenerative capacity. The method does this by expressing both resource demand and supply in terms of area necessary to support these flows. The use of an area as a measure of life-supporting natural capital was chosen to underline that many basic ecosystem services and ecological resources are driven by areas where photosynthesis takes place , showing in this way how humanity is constrained by nature’s negentropic capacity to transform low quality solar energy into high quality chemical energy and living matter." (https://www.researchgate.net/publication/234092351_An_overview_on_ecological_footprint_and_sustainable_development_A_chat_with_Mathis_Wackernagel)
"The ecological footprint (EF) was developed at the University of British Columbia by Dr. William Rees and Dr. Mathis Wackernagel. It estimates how much of Earth's productive land and sea is used to produce the food, materials and energy that we consume and to assimilate our wastes. The EF looks behind the scenes to see what it takes to make an alarm clock, a cup of coffee, clothes, a home or to operate an automobile. This gets complicated in our global economy where the products originate from around the world." (http://radicalsimplicity.org/footprint.html)
"Institutionalizing the Ecological Footprint at the national level requires acceptance by statistica loffices, policy advisors, academia and businesses of the methodology and data underlying the Foot-print.
To influence these decision makers and accomplish our overarching mission, we are working with 73 partner organizations around the world to carry out four key programs:
• National Footprint Accounts Research: We maintain and update the National Footprint Accountsfrom 1961 to the present for 152 nations. These accounts provide the underlying data sets for allFootprint analyses worldwide. We coordinate the research necessary to refine these accounts.
• Standards: The adoption of the Ecological Footprint is dependent on Footprint analyses being conducted consistently and rigorously, and the results being reported in an unbiased manner. Therefore,we have created a consensus-based process for establishing standards governing all Ecological Footprint calculations worldwide. The first Ecological Footprint standards were launched in June2006.
• Network Building and Outreach: We are building a network of the world’s leading practitionersand institutions, which are working to advocate the Ecological Footprint. The network nowincludes 73 partner organizations on six continents. Through our newsletter, website, trainingand media work we are sparking a global dialogue about ecological limits and overshoot.
• Applications: Working with our partner organizations we are applying the Ecological Footprintin innovative ways in education, business and government. These applications create recognitionof overshoot, demand for action and tools to drive institutional change. We carry out all of our programs in active collaboration with our partners. Our diverse partner network includes the key players worldwide that are using the Ecological Footprint in education, government, business and academia, such as WWF with 5 million supporters, ICLEI with 475+ member cities worldwide, and government agencies such as the Ministry of Environment in Finland and EPA Victoria in Australia. Our partners make the Ecological Footprint relevant and practical in the countries in which they operate, create innovative applications, and through their collaboration with us and each other, increase penetration of the Footprint across the globe. Partners participatein our standards committees, and pool resources in innovative projects that accomplish much more than any one of us could on our own." (https://www.researchgate.net/publication/234092351_An_overview_on_ecological_footprint_and_sustainable_development_A_chat_with_Mathis_Wackernagel)
Why use hectares and not energy ?
From an interview of Mathis Wackernagel, by Alessandro Galli:
* "What does the EcologicalFootprint tell us?
MW: Humanity is now consuming more than the Earth can produce. Our economies operate as ifecological resources are limitless, without recognizing that this ever-increasing consumption is under-mining the Earth’s ability to provide for us all. Today, humanity’s demand on nature, its EcologicalFootprint, is 25% greater than the planet’s ability to meet this demand. It now takes the Earth one year and three months to regenerate what we use in a year. This global ‘ecological deficit’ or ‘overshoot’is depleting the natural capital on which both human life and biodiversity depend.The consequences of this environmental pressure are already evident. Collapsing fisheries, loss of forest cover, depletion of fresh water systems, accumulation of CO2in the atmosphere and thebuild-up of wastes and pollutants are just a few noticeable examples. If continued, overshoot willpermanently reduce the Earth’s ecological capacity and lead to ecological collapse and social misery. While these trends affect us all, they have a disproportionate impact on the poor, who cannotbuy themselves out of the problem by getting resources from elsewhere. To reverse this trend, it is imperative that individuals and institutions all around the world recognize the reality of ecologicallimits and start making decisions consistent with these limits. By scientifically measuring the supply ofand demand for ecological assets, expressed in hectares of land area, the Ecological Footprint provides a resource accounting tool which reveals ecological limits, helps communicate the risk of overshoot, and facilitates sustainable management and preservation of the Earth’s critical ecological assets.
* AG: From a thermodynamic perspective, why don’t you just use energy rather than hectares as themeasurement unit?
MW: Surface is a good indicator for life because it is where life happens (and we can map everythinghappening above and below it to a surface, much like a classical map does). In other words, we could say that the Earth is the biggest solar collector available: its surface captures solar energy that, through photosynthesis, can produce biomass. There need to be other conditions as well (enough water, etc.,) to sustain life but surface is a limitation and it is probably a good first approximation for measuring biocapacity. We go a step further since we are not measuring in hectares, but global hectares. Inother words, we adjust each surface according to its productivity. One hectare of Sahara, even thoughit receives a lot of sun, does not represent the same productivity as one hectare of Amazon forest. Amazon forest has a much higher ability to regenerate biomass, so we count it as more global (i.e.standardized) hectares according to our mechanics system. But then again, why surface, why not energy? Energy can be very confusing because through the energy cascade from the initial solar flux tothe final carrot we eat we have enormous differences in energy. The sun powers the Earth with about1.75E+05 TW constantly but some of this has been reflected in the stratosphere from clouds, etc.and therefore not everything reaches the ground. But that is the power we get from the sun. Now these 1.75E+05 TW are translated through photosynthesis into a Net Primary Productivity (NPP)of the planet of perhaps 100 or 200 TW, about 1000 times less. And, not all of NPP is usable; we have to ask: ‘how much of that become food for us?’ Human food production uses about 40% ofthe biological capacity of the planet, and that corresponds, in a first approximation, to a food intakeof 2,500 Kcal/day per person. Considering a world population of 6.5 billion people, this leads to anamount of less than 1 TW – again about a factor of 100 less than the NPP. At what stage in the energy cascade do we measure? How do we make sure people do not confuse solar Watts with NPP Watts,or food Watts? Also, if we provide results in TW people do not understand what a TW means but if the results are provided in hectares, or acres, people can easily understand how big they are, since 1 acre is the extent of a soccer field. So the cascade effect, the quality effect, the exergy effect or the entropy effect is directly captured by considering the quality of the area to capture the energy and make some useful biomass out of it. For some scientists, our approach may be a bit confusing since we are measuring aflow in terms of the stock necessary to provide this flow. Just think of it like this: consuming 10 kg of tomatoes a year means continuously occupying a few square meters of garden space that can grow these tomatoes. So that is why I think, from an accounting perspective, it is easier to use hectares, and it doesn’t lead to that easy confusion that we have when looking at energy flows or energy cascades, where th eenergy quality leads to a very rapid reduction in the available energy from 1.75E+05 TW down to1 TW, and where confusion can arise easily when one Watt is compared to another Watt." (https://www.researchgate.net/publication/234092351_An_overview_on_ecological_footprint_and_sustainable_development_A_chat_with_Mathis_Wackernagel)