In Part 1, we looked at how nature works on a fundamental level. In the end, we asked ourselves how we can fit better in the earth system and what sustainability is. In this Part 2, we briefly look at different formulations of sustainability and consider a failed example to sensitise us to what is relevant to sustainability.
There are many ways of looking at sustainability because it has many aspects , . Apparently, sustainability has to do with quantities: how much we take, do and dump. Most definitions set a normative goal  aimed at humans rather than the biosphere. For example, with the often quoted definition:
“Sustainable development means meeting the needs of the present without compromising the ability of future generations to meet their own needs” .
Definitions like this do not show how to be sustainable. And I think in many parts of the world it is our wants, not our needs, that make us unsustainable.
More specific definitions of sustainability assume at least a relationship between two interacting systems, described by cybernetics :
“Sustainability is a dynamic equilibrium between a population and its carrying capacity, such that the population evolves without having irreversible negative effects on the carrying capacity” .
It is often not enough to look at just two interacting systems. An example is fisheries and only monitoring one species of fish. In the Baltic Sea, for example, cod, herring and sprat are the three dominant species. Cod feed primarily on adult sprat, while sprat tend to eat the cod’s eggs and larvae. If cod are overfished -> the number of cod decreases -> the number of sprat increases -> the number of cod eggs and larvae decreases -> cod decline even faster than expected.
Another definition of sustainability therefore emphasises the feedback loops with an entire system in the biosphere , which can be described for example by information theory :
“Sustainability can be operationally defined as a feasible set of flows (such as materials, energy, people, information, currency) that can be sustained despite changes in the environment” .
Approaches such as this recognise that every living being leaves a footprint that causes change, and such theories
- give us tools to understand how systems reconfigure themselves in response to change,
- and how robust or vulnerable systems are to these changes.
For example, it makes sense for a government to set a maximum amount for each pollutant that factories are allowed to discharge into a river. However, the concentrations of these pollutants in water are not the parameters that tell us how vulnerable the natural system really is. In fact, it is often difficult to see the dynamics of the natural system and to answer the question: How do we know when we are about to become unsustainable?
Instead of going into more detail about how information theory finds such crucial parameters, I give a current example of fisheries in Europe.
This graph  shows in blue the amount of cod commercially caught each year in the western Baltic Sea. It has been declining for 25 years. Every year, the ministers of the EU Council agreed on the amount of allowable catches, which is shown in red. This amount has also declined, and ministers sometimes talk about slashing quota. However, look closely: Their imposed limit was almost always higher than the fishing industry was able to catch, so the EU council maintained in fact unregulated fishery, and catches declined due to overfishing, not due to regulation.
The EU council was advised by ICES, the International Council for the Exploration of the Sea , as shown in orange. This is the oldest intergovernmental scientific organisation in the world, but its advice was also mostly above the actual catches. You may wonder why. A look at its organisational structure  makes it clear that politics has the say, not its network of 6000 scientists, to address “societal needs for … sustainable use of our seas and oceans” . I find two points revealing. First, politicians (the EU Council) should be directly advised by a scientific body, not by politicians. Second, the scientists do not include the ecological context. This is unfortunate. The following graph gives you an example of such a context, measured by marine biologists . It shows the productivity of the cod population as a function of sea surface temperature for each year:
Graphs like this reveal that cod are not only overfished (which shifts the data points vertically downwards), but during the past two decades (red), warming seas have inhibited spawning. These biologists have also measured many other parameters of the fish stock and analysed their interrelationships and have concluded that the western Baltic cod has already surpassed the threshold of collapse in the early 2000s. Recovery is very unlikely .
I feel a great sense of loss when I read through such scientific literature . And I think a typical pattern is the following. ICES still advises EU ministers to “recover the stock to its maximum sustainable yield by 2021” , . To talk about “maximum sustainable yield” for a fish population that has been declining for 25 years is contrary to science, you don’t have to be a scientist yourself to judge that. I call it an abuse of the work of the 6000 scientists in the ICES network. And I wonder where the voices of these scientists are. Furthermore, the Danish Small-Scale Fishermen’s Producer Organization (FSK-PO) and BSAC (the Baltic Sea Advisory Council) recommend that a “transition to low impact fishery [of cod] should take place gradually 2021-2027” . Look again at the blue graph above. Where is it likely to be in 2027?
Indeed, social scientists have noted that public perceptions also lag behind ,  and that many of us still believe that collapsed ecosystems recover. But they don’t, because:
Sustainability has to do with well-functioning systems, often complex systems. A collapsed system does not recover; it often takes a long time for a new system to evolve.
To come back to the definition of sustainability in terms of information theory: A few obvious parameters are often sufficient to recognise that problems are imminent . In the cod example, these are the decreasing catches and the decreasing average fish size. However, any fishery results in a smaller fish size, and the crucial question is: how far can we go to still conserve the fish stock? This is not trivial. But I hope I have been able to convince you that the collapse could have been prevented if the relevant parameters of cod stocks had been identified and monitored, so that early warnings and effective fishing quotas could have been given to politicians — and on the political side, far-sighted consequences would have been necessary. By “far-sighted” I mean in this case only 20 years: the cod population would now be in a sustainable state and the Baltic fishery would have more employees than it does now.
To know whether one of our activities is sustainable or not, and to know how far we can go to keep it sustainable, we must find a set of relevant parameters of the natural system we are affecting and monitor these parameters carefully. Finding these parameters is not trivial, as many natural systems are complex. So, better be cautious with promises.
To put the Baltic cod fishery in a global context: The Food and Agriculture Organisation of the United Nations (FAO) describes about 60% of the world’s fish stock as “maximum sustainably fished” – how do they know what the maximum is? Do you trust? And it calls 35% “unsustainably fished”, while only the remaining 5% is called “underfished” .
Given these definitions and failures of sustainability, how can we better fit into the earth system in concrete terms? This is the topic of the next blog, Part 3.
Until then, I wish you all the best
 C. A. Ruggerio, “Sustainability and sustainable development: A review of principles and definitions,” Science of The Total Environment 786 (2021). https://doi.org/10.1016/j.scitotenv.2021.147481
 P. Glavič and R. Lukman, “Review of sustainability terms and their definitions,” Journal of Cleaner Production 15 (2007). https://doi.org/10.1016/j.jclepro.2006.12.006
 Wikipedia, “Normative statement. ”https://en.wikipedia.org/wiki/Normative_statement
 G. H. Brundtland et al., “From one earth to one world,” Habitat International 11 (1987).https://doi.org/10.1016/0197-3975(87)90004-X This quote is taken from p. 14 and it goes on: “The concept of sustainable development does imply limits – not absolute limits but limitations imposed by the present state of technology and social organisation on environmental resources and by the ability of the biosphere to absorb the effects of human activities.”
 Wikipedia, “Cybernetics”. https://en.wikipedia.org/wiki/Cybernetics
 M. U. Ben-Eli, “Sustainability: definition and five core principles, a systems perspective,” Sustainability Science 13 (2018). https://doi.org/10.1007/s11625-018-0564-3 This quote is taken from p. 1340 but I omitted “[…such that the population develops] to express its full potential” because I find this too arbitrary. I also disagree for example on his first principle on p. 1341: “Contain entropy”. This does not make physically sense, as explained in the previous blog Part 1.
 A. L. Mayer, R. P. Donovan, and C. W. Pawlowski, “Information and entropy theory for the sustainability of coupled human and natural systems,” Ecology and Society 19 (2014). http://dx.doi.org/10.5751/ES-06626-190311
 Wikipedia, “Information theory”. https://en.wikipedia.org/wiki/Information_theory
 ICES, “Cod (Gadus morhua) in subdivisions 22–24, western Baltic stock (western Baltic Sea),” (2019). https://doi.org/10.17895/ices.advice.5587
 ICES, “International Council for the Exploration of the Sea.” https://www.ices.dk/Pages/default.aspx
 Wikipedia, “ICES organisational structure.” https://en.wikipedia.org/wiki/International_Council_for_the_Exploration_of_the_Sea
 ICES, https://www.ices.dk/about-ICES/who-we-are/Pages/Who-we-are.aspx
 C. Möllmann et al., “Tipping point realized in cod fishery,” Scientific Reports 11 (2021).https://doi.org/10.1038/s41598-021-93843-z
 J. Holland, “ICES recommends slashing North Sea cod quota, NGOs respond,” Seafoodsource, 01-Jul-2019. https://www.seafoodsource.com/news/environment-sustainability/ices-recommends-slashing-north-sea-cod-quota-ngos-respond
 M. Earle, “Maximum sustainable yield in the EU’s Common Fisheries Policy – a political history,” ICES Journal of Marine Science (2021). https://doi.org/10.1093/icesjms/fsab037
 “Proposal: Western Baltic Sea should be fished using low impact fishing gear,” Danish Small-Scale Fishermen’s Producer Organization (FSK-PO), Sep-2020. http://www.bsac.dk/getattachment/BSAC-Resources/Documents-section/BSAC-Newsletter-latest/Proposal-to-transform-fishing-in-western-Baltic-to-low-impact-gear.pdf.aspx?lang=en-GB
 M. Ergazaki and G. Ampatzidis, “Students’ Reasoning about the Future of Disturbed or Protected Ecosystems & the Idea of the ‘Balance of Nature,’” Research in Science Education 42 (2012). https://doi.org/10.1007/s11165-011-9208-7
 R. J. Ladle and L. Gillson, “The (im)balance of nature: a public perception time-lag?,” Public Understanding of Science 18 (2009). https://doi.org/10.1177/0963662507082893
 Wikipedia,“Sustainability metric and indices.” https://en.wikipedia.org/wiki/Sustainability_metrics_and_indices
 Food and Agriculture Organization of the United Nations (FAO), “The State of World Fisheries and Aquaculture 2020,” (2020). https://doi.org/10.4060/ca9229en
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