Sustainability, behind the catchy word

What is sustainability?

Just like the word “energy”, our common understanding of the word “sustainability” is a bit fuzzy. When we see it written, we often interpret it as “something good for the environment”. The purpose of this article is to propose a clearer scientific definition of “sustainability”. Introduced in the Brundtland Report for the World Commission on Environment and Development in 1987, sustainable development is defined as a “type of development that meets the needs of the presents without compromising the ability of future generations to meet their own needs” [1]. We rely on the use of natural resources for our economic activity and to achieve a certain level of well-being [2].

However, when the depletion rate of natural resources and the rate of waste production are higher than what Earth can naturally produce and absorb, the environment is put under pressure, and future generations will have to cope with less ecological capital [3].

Sustainability refers to the system state where humans live below the natural regenerative capacity of the biosphere [3].

Can it be measured?

The concept of ecological footprint is a way to measure the sustainability state of humanity, a country or even an individual [4]. The ecological footprint is defined as the amount of biologically productive area (measured is global hectares which represent an average world productivity) needed to support a human activity [4]. For instance, our activities require food, space for buildings, wood, metals and space to absorb our waste (among which carbon emissions).

When the ecological footprint is higher than the biocapacity of the Earth, net destruction of ecological capital occurs [3]. It is a bit like if you were spending more money than you earn and someday, a bailiff came to cease your personal belongings (e.g. car, house, furniture) to pay off your deficit. For example, in 2014, an average Norwegian had an ecological footprint of 6 gha (global hectares) whereas the total biocapacity of the Earth is 1.68 gha [5]. Although Norway is often pointed as a sustainability example, if everyone on Earth lived as an average Norwegian, humanity would need  planet Earths to sustain such a lifestyle. The following graph shows the number of Earths that would be required to sustain the lifestyle of an average inhabitant from different countries in 2014:

The unpaid debt

Few countries have an ecological footprint per capita below the world biocapacity [5]. Besides, the world average ecological footprint (1.7 planet Earths) is higher than the world biocapacity as shown on the last graph. Indeed, humanity has already overshot the long-term global carrying capacity of the Earth, and the crossing point occurred around 1970 as shown on the graph below [5].

In other words, humanity has been living unsustainably since 1970 by accumulating an ecological debt which is not likely to be repaid soon [6]. In fact, under a business-as-usual scenario, 2.6 planets would be needed by 2050 to sustain humanity’s depletion rate [6]. A complex system like the environment cannot stay out of an equilibrium state for too long. The way complex systems behave to seek equilibrium is probably better explained by the following quotation from the 1972 “Limits to Growth” [7]:

“Once the population and economy have overshot the physical limits of the earth, there are only two ways back: involuntary collapse caused by escalating shortages and crises, or controlled reduction of the ecological footprint by deliberate social choice.”

Elliot MARI

Energy Researcher at Sustainable Energy Network Solutions