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The Luxembourg Overshoot Day 2020 - what does it really mean?

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Veröffentlicht am Freitag, den 21. Februar 2020

We rely heavily on numbers and complex measurement regimes to direct our attention and allocate our resources. Quantitative measurements represented in figures and graphs tell us whether we are doing well, how we compare, where to go, and whether we are progressing towards a desired state.

In our quick-paced lives these pointers are the basis for many a fast decision. But what if indicators we rely on are controversially discussed by experts? We are all familiar with contradictory advice on our diets: How much fats or sugars should we really eat? Experts contradict each other in an increasing number of fields. How can we still rely on indicators with peace of mind, knowing that a highly precise expression of an indicator provides no guidance on its accuracy?

Abstract aggregate indicators, such as numbers that determine the Earth Overshoot Day globally or for one country, are not simple truths that can be deducted from direct observations of nature and social practice. Such indicators are designed with the intention to simplify complex situations, often for the purpose of comparisons or communication. First design choices on how to construct an indicator involve making judgments on which data to collect (the data is often heterogeneous and uncertain). Subsequently, the data is processed using specific methods that involve simplifying assumptions and conventions that may not be equally applicable to all situations that are assessed in the end with the help of the indicator.

The Earth Overshoot Day is the day when according to the calculated ecological footprint humanity has used up a full year’s worth of the supply of resources the planet can provide. In 2019 the global overshoot day was on 29 July. In 2020, Luxembourg reached its national Overshoot Day on which it had consumed all resources for one year on 16 February.

The ecological footprint is one of the most widely known environmental indicators to calculate environmental impacts from nations, organisations or our own impacts on a personal basis. First developed by Mathis Wackernagel and William Rees in the 1990s, it measures human consumption of products and services from different ecosystems in terms of the amount of bio-productive land and sea area. It calculates the total land area needed to produce food and fibre resources, the energy we use, and land areas required to absorb CO2 emissions by the supply chains. As this land is distributed globally, this measure is expressed as a unit called ‘global hectares’. The biocapacity of a land area represents its ability to meet human demand for material and energy consumption and waste disposal and absorption of CO2 emissions. The footprint distinguishes six land-use types with different biocapacities, including grazing land, cropland, built-up land and the sea (for more details see the website of footprintnetwork).

Everyone can personally impact their contribution to the global, national or personal footprint, for example by adapting travel, tourism and commuting habits, dietary choices and electricity supply, or by avoiding food waste and overconsumption of consumer items.

The case of Luxembourg is interesting as it clearly shows the merits and limitations of such a tool that relies on the aggregation of a large number of different data. It is an excellent tool for communication and awareness raising that effectively triggers debate. But, like all selective images and representations, there are dimensions of the situation that it suggests, reveals, but also some that it distorts and conceals.

The national average is calculated by dividing the national consumption by the population number. However only two environmental impacts are considered: CO2 emissions and land use. Despite the fact that the “ecological footprint” suggests a comprehensive approach, it does not include water consumption or solid waste production.

The example of Luxembourg also demonstrates how aggregates, especially if expressed on a per capita basis, can give a distorted picture of actual behaviour: national consumption statistics include all fuel purchases on the national territory (including by tank tourists and cross border workers), as well as the cross-border commuters’ consumption of other products and services including food. But even if we consider only residents’ contribution to the average consumption in Luxembourg, this remains very high.

Moreover, several steps in the calculation process, such as crop yield and equivalence factors used were not made transparent. The scientific basis for the weighting of different factors in the aggregation of data is not clearly explained. The spreadsheet used to make these calculations is patented and proprietary, and as such not published, so that the exact method and underlying assumptions cannot be verified. These shortcomings contributed to the fact that the method for calculating the ecological footprint has not been accepted by EUROSTAT as a basis for official statistical indicators.

However, all these criticisms are well addressed on the movement's Overshoot Day website. And it can be argued that neglecting to represent uncertainties and using certain approaches to aggregation are shortcomings not more severe than those present in other widely used complex sustainability indicators.

Ecological footprint and overshoot calculations (just as many other simplified aggregate sustainability indicators) are not an exact science. Science addressing challenges in complex dynamic systems rarely is. There is no simple ‘true or false’ in such assessments. The engaged person must make their own assessment of the quality of information based on the purpose they want to use this information for. But one thing is certain – indicators such as the ecological footprint and the associated Earth overshoot day have great communicative value to trigger reflection on what we know and how we act. Critical analysis and debate on these topics are a vital basis for societal learning on how we might better address such complex sustainability challenges.


Ariane König & Paula Hild University of Luxembourg
Jerome Ravetz, Associate Fellow, Oxford University

Further reading:

Mathis Wackernagel, & Bert Beyers. (2019). Ecological Footprint: Managing your biocapacity budget. New Society Publishers: Global Ecological Footprint Network.
Jerome Ravetz, Paula Hild, Olivier Thunus, and Julien Bollati (2018). Sustainability indicators: Quality and quantity. In A. König (ed.) Sustainability Science: Key Issues. Routledge. Pp. 271-295.
Rockstrom, J., Steffen, W., Noone, K., Persson, A., Chapin, F. S., Lambin, E. F., Foley, J. A. (2009). A safe operating space for humanity. Nature 461 (7263): 472–475. doi:10.1038/461472a