Le « jour du dépassement », argument en faveur d’une agriculture productive  

"It's an indicator we could have done without, but whose return now sadly punctuates each of our summers: Earth Overshoot Day - the date that marks, each year, the day when humanity has consumed all the resources that our planet is capable of producing in a year.", noted the French Development Agency in its news bulletin of August 28. Unprecedented since 1970, this day, which has become a symbol of the overexploitation of resources resulting from human activities, falls this year on Saturday, August 22, three weeks later than in 2019. (…) In 2020, the equivalent of 1.6 planets will still be needed to meet humanity's needs."Most French media outlets have also taken up, without much nuance, the announcement by the American NGO, the Global Footprint Network, which is behind this calculation.

Such a presentation contrasts with the criticisms made by many researchers in sustainable development.[1] and the abrupt judgments made by certain opinion organs, which do not hesitate to describe the day of the overshoot as "false theory"[2] and of"intellectual scam"[3]. So, what is this indicator worth?

The day of overshoot is determined by comparing the"ecological footprint" human activities and the "bio-capacity" of the planet. The ecological footprint represents the quantity of natural resources that the population needs to feed itself, house itself, move around and compensate for the waste it generates, including greenhouse gases; it corresponds in a way to the demand for nature. Biocapacity is the Earth's capacity to produce the resources consumed by the ecological footprint; it is equivalent to the supply of nature. Both the demand and the supply of nature are expressed, on the basis of certain conversion coefficients, in "global hectares", representing the surface area necessary to, respectively, consume and produce the resources concerned. This surface area is calculated each year, for each country, by the Global Footprint Network (GFN), from thousands of data compiled by international organizations.

There is " exceeding " when the ecological footprint, in global hectares equivalent, exceeds the bio-capacity of the planet. Thus, in 2020, the GFN considers that the ratio between these two variables is 1.6, in other words, that the planet has consumed 1.6 Earths[4]. To further impress, this figure is converted into "ecological debt" annual: humans would consume the Earth's renewable resources in a certain number of days and live "on credit" the rest of the year[5]According to the GFN, the ecological debt has continued to grow over the past half century: Earth Overshoot Day moved from December 20 in 1971 to July 31 in 2019. The reversal of the trend recorded in 2020 – the fateful date occurring on August 22 – would be temporary, as it is due to the reduction in economic activity and the containment measures put in place across the world in response to the Covid-19 pandemic.

This method of calculation is questionable for several reasons. The main one is that the ecological footprint of CO2 emissions is expressed in terms of the area of forests theoretically needed to absorb these emissions (taking into account the carbon sequestered by the oceans). In doing so, this indicator, which is intended to be purely accounting[6], slides towards the normative: we can in fact proceed in many other ways, less consuming of space than forests, to reduce the carbon footprint linked to the use of fossil energy; in particular, developing nuclear energy or renewable energies. As the researcher Bjorn Lomborg suggests, in the form of a semi-joke,[7] : why, for example, not translate CO2 emissions into equivalent surface area of solar panels?

This criticism is all the more legitimate since CO2 emissions today represent, in global hectares, nearly 60 % of the global ecological footprint, compared to 44 % in 1961. In addition, the other categories of land use studied by the GFN – crops, meadows, wood products, fishing areas, built-up areas – have an ecological footprint less than or equal to their biocapacity.[8] (chart). Therefore, the method chosen to assess the carbon footprint is crucial and largely determines, on its own, the exceeding of the biological capacities of the planet and the date on which it is expected to occur.[9]According to some experts, it would be better to abandon a single indicator and clearly distinguish between problems related to the consumption of natural resources and those caused by the use of fossil energy.

Another troubling point: paradoxically, and contrary to what one might suppose, the GFN calculations do not take into account other phenomena that are major symptoms of the ecological crisis – but which are difficult to express in equivalent hectares – such as the erosion of cultivated land, the scarcity of water resources, the depletion of fish stocks, the reduction in biodiversity or even the pollution of water, air and soil. Thus, while they tend to overestimate the ecological footprint by translating carbon dioxide emissions into equivalent forest areas, these calculations underestimate the degradation of natural resources and agro-systems, which the GFN also acknowledges.[10].

Earth Overshoot Day is the subject of many other criticisms. Its very usefulness for public policy is contested, due to its methodological limitations. It nevertheless has symbolic value and can help alert public opinion to the scale of environmental challenges and their evolution over time and space.[11], provided it is accompanied by detailed "instructions for use." Farmers, often accused of productivism, can rest assured: this concept directly advocates an increase in agricultural yields, to the extent that this allows humanity to feed itself without encroaching on natural environments. But we also need to produce better, to reduce the pressure of agriculture on the environment. Even if Earth Overshoot Day has a certain educational function, we need better agro-ecological indicators.

[1] See in particular: Jeroen van den Bergh and Fabio Grazi, “On the Policy Relevance of Ecological Footprints”, Environ. Sci. Technol. 2010, 44, 4843-4844; Linus Blomqvist et al., “Does the Shoe Fit?” Real versus Imagined Ecological Footprints”, PLOS Biology, November 2013; Jeroen van den Bergh and Fabio Grazi, “Reply to the first systematic response by the Global Footprint Network to criticism: A real debate finally? », Ecological Indicators 58 (2015) 458-463; Lu Zhang et al., “Validity and utility of ecological footprint accounting: A state-of-the-art review”, Sustainable Cities and Society 32 (2017) 411-416; Robert B. Richardson, “Resource depletion is a serious problem, but 'footprint' estimates don't tell us much about it,” The Conversation, July 24, 2019.

[2] Counterpoints, July 31, 2019.

[3] Agriculture and Environment, May 2018.

[4] In 2019, the global ecological footprint was 2.7 hectares and the Earth's biocapacity was 1.6 hectares. The ecological footprint was therefore equivalent to 2.7/1.6 = 1.7 Earths. Note that the 2019 results are calculated based on data available for 2016.

[5] In 2020, the planet would have "consumed" approximately 1.6 Earths in 365 days, or, according to more precise data (not rounded), 1 Earth in 235 days. The day of the overshoot would therefore be the 235th.^th day of the year, August 22.

[6] According to a study by Mathis Wackernagel, president of the Global Footprint Network, and other researchers, “The ecological footprint is the sum of all human activities that require bio-productive land, (…) [it] does not ‘dictate’ how societies should develop. Defining the ecological footprint as an accounting framework rather than a normative indicator of progress allows this measurement system to be applied to many contexts, which is a key element of sustainability assessment frameworks.” (David Lin et al., “Ecological Footprint Accounting for Countries: Updates and Results of the National Footprint Accounts, 2012-2018”, Resources 2018, 7, 58).

 [7] Quoted by Agriculture and Environment August 24, 2020.

[8] By construction, the ecological footprint of crops, as measured by the GFN, cannot exceed the cultivated area. It represents, on a global scale, 19 % of the total ecological footprint.

[9] Another problem with expressing carbon dioxide emissions in terms of the forest area needed to absorb them lies in the choice of CO2 absorption coefficients. Since 2016, the GFN has used three separate coefficients, intended to reflect the carbon absorption capacity of three types of forest cover: primary forests, secondary forests, and plantations. The adoption of these coefficients led, between 2012 and 2018, to an upward revision of 21 % of the planet's carbon footprint estimated for 2008 (David Lin et al., op.cit.).

[10] “The ecological footprint does not assess the level of degradation or the long-term implications of resource use for ecosystem productivity. It is not a comprehensive assessment of sustainability and is most useful when complemented by other relevant measures.” (David Lin et al., op.cit.).

[11] According to the GFN, all regions of the world would be in "ecological deficit" (i.e. would have an ecological footprint, measured in global hectares, greater than their biocapacity), with the exception of South America and the Europe zone outside the European Union (which notably includes Norway, Switzerland, Russia and Ukraine), which have a large forest cover. Expressed in hectares per person, the ecological deficit in 2019 would be the lowest in Africa (- 0.2 ha) and the highest in North America (- 2.8 ha), just ahead of the European Union (- 2.5 ha). Based on statistics provided by the GFN, it can be estimated that emerging countries ("middle-income", according to the World Bank classification) are responsible for 55 % of the planet's ecological deficit, ahead of high-income countries (45 %). Low-income countries have a globally zero ecological deficit.