A human being may only appropriate a part of nature if there is enough, and as good left to others. Three centuries after the philosopher John Locke formulated this rule it is more relevant than ever. But how can we observe this ‘Lockean proviso’ in the exploration of raw materials which nature cannot replenish? The more metallic and phosphate ores we extract from the soil, the fewer are left for our descendants. What may future generations demand from us?

A thought experiment on the basis of the science fiction film Interstellar brings the issue into focus. The thriller Interstellar sketches a grim picture of the future. Food shortages have decimated the world’s population. The American space agency NASA sets out to leave the exhausted Earth. Thanks to the heroes of the film, a number of courageous astronauts, a planet outside our solar system is found which seems fit for human habitation. In giant spaceships the survivors journey to this exoplanet.

Interstellar ends before we get to know if the people involved indeed manage to reach the exoplanet and survive. Of course they are sure to succeed, as the film is steeped in technological optimism. The makers wanted to stand up for pioneering science and space travel. A good chance that the sequel will be a quest for other inhabitable planets, even farther away in the universe.

Social contract

For those not carried away by this kind of technological optimism, one scene is missing in Interstellar. Wouldn’t there be those who, before embarking on a voyage to this new exoplanet, would insist on agreements being made to prevent the new planet from becoming exhausted, as happened to the Earth? It can never be mankind’s intention to plunder one planet after another, forcing its offspring time and again to venture into perilous planet-hopping.

The dialogue about these agreements is all the more exciting as the participants do not yet know which generation on the exoplanet they will belong to. If every spaceship follows its own trajectory, then the sequence of generations can turn into a considerable mess. Close to heavy celestial bodies, time slows down. Approaching a black hole, it virtually comes to a standstill. One of the astronauts in Interstellar experiences Einstein’s laws of gravity in a painful way when he ends up standing at the deathbed of his aged daughter.

It is in the interest of the fastest space travellers – the first to arrive on the exoplanet – to transform the natural resources of the planet into comfort and civilisation. Slow travellers, arriving many generations later, would benefit from the economical use of natural resources, as otherwise they would end up on yet another exhausted planet. Before their departure from earth space, travellers don’t know which generation they will end up in, and they are forced to look at the issue from both perspectives. That enhances the chances of agreement being reached.

The makers of Interstellar have missed the opportunity to portray a unique social contract; a contract between various generations on the distribution of natural resources. A contract that has come about in an honest way: as no one knows which generation they are going to be a part of, no one can push the interests of one generation. In addition to being science fiction, the film could have been interesting ethics fiction with the veil of ignorance as special effect.

Limited raw materials

In formulating their generation contract, the planet-hoppers do not have to start from scratch. In the course of centuries the Lockean proviso – enough and as good left for others – has been elaborated into a series of ethical and legal principles on the use of natural resources. The most noted principle is incorporated in the sustainability definition of the Brundtland Committee, drawn up in 1987 for the United Nations: sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

The Brundtland definition can be applied to renewable natural resources: air, water, timber, fish; we can make endless use of these, provided we do not disturb the natural cycles all too roughly. But pollution and overexploitation of the earth’s ecosystem indeed do damage to the chances of future generations. International environmental policies are now aimed at saving renewable natural resources.

Countries try to reach agreement on countering climate change, air pollution, freshwater scarcity, deforestation, overfishing and the decline in biodiversity. This is such a daunting task that the international community has hardly got round to dealing with the much more complicated issue of non-renewable natural resources, such as metals and phosphates. The metals in the Earth’s crust came to be there in the formation phase of the Earth or by later cosmic impact. Phosphate was formed in millions of years, largely from dead plants and animals that had sunk to the seabed. These mineral reserves cannot be recovered in natural cycles, at least not on a human time scale.

The Brundtland definition can only with difficulty be applied to non-renewable raw materials. After all, the metallic and phosphate ores that are now being extracted from the Earth’s crust are lost to future generations. Moreover, the richest, most easily reachable and least polluting ores are mined first. The sooner they become exhausted, the less profitable mining becomes.

The mining of minerals, in short, seems incompatible with sustainable development in terms of Brundtland. Unless we take for granted that these raw materials will never be depleted anyway…

Optimists and pessimists

In scientific circles, there is a lively debate between raw material optimists and pessimists. The optimists point out that the majority of chemical elements in the periodic table, from metals to phosphorus, are abundant in the Earth’s crust. If the rich ores run low, humans will find a way to extract minerals from less concentrated ores, or even from common rock. The increase in prices of scarce minerals will stimulate the development of new mining technology.

Raw material optimists feel confirmed by Thomas Malthus’ faulty forecast. In 1798 this economist predicted a great famine: there would be too few natural resources, particularly arable land, to feed the rapidly growing population. He underestimated the growth in productivity which agriculture would see. Now, in 2015, the world’s population is seven times bigger than in 1798, but there is more than enough food available (if it were apportioned more evenly). Malthus has ended up on the dung heap of history.

Raw material pessimists expect a limit to the mining of increasingly lower mineral concentrations. Beyond this ‘mineralogical barrier’, mining costs too much in terms of energy and raw materials, or would inflict too much damage on nature and the environment. There may come a moment when, for the manufacture of mining machines, more metal is needed than these machines can mine during their lifetime…

A UN expert group estimated that only 0.01 percent of the total amount of an element can actually be mined in the uppermost layer of the Earth’s crust – roughly 1,000 meters. On the basis of this estimate, researchers from the University of Utrecht have calculated when the recoverable reserves of sixty mineral ores will have been exhausted.

Assuming that from 2050, every world citizen will be consuming the same amount of metals as the present population in the industrialised world, the researchers conclude that antimony will have been exhausted before 2050; gold, zinc and molybdenum within a century; and thirteen other metallic ores within a thousand years.

Most policymakers side with the optimists. They believe the depletion of non-renewable raw materials won’t get that bad. Both the European Commission and the Dutch government have drafted a list of ‘critical raw materials’, focusing on geopolitical instead of physical scarcity. Europe lacks raw materials. Quite a number of minerals are only mined in a limited number of countries, including China.

Often these are countries of unreliable regimes, who might cut off the supply of raw materials out of protectionist motives or as a result of conflict. The European and Dutch policy towards raw materials is aimed at promoting a free market for raw materials and widening the number of suppliers, making sure that the European manufacturing industry doesn’t have to contend with supply problems.

Circular economy

We also find raw material optimists among the advocates of the circular economy. If we stop dumping the raw materials in our products in the form of garbage, but reuse them in new products, we create a cycle that copies nature. The raw materials remain available infinitely, and, as a result of which, we do not need to extract them from the earth’s crust. Dutch sustainability Professor Herman Wijffels even predicts an “abundance of raw materials, thanks to reuse”.

Pessimists are in agreement about the importance of recycling raw materials, but point out that we won’t be able to manage only with recycled raw materials as long as our material consumption and the world’s population keep growing. Moreover, the circular ideal of one hundred percent recycling faces obstacles. Recycling raw materials down to the last percent requires excessive amounts of energy. Take the iron used in ships’ hulls for instance, whose rusty remains are discarded in the sea. What are the means of recovering it?

Both raw material optimists and pessimists emphasise the importance of substitution: the use of the most scarce raw materials can be scaled down if they are replaced by less scarce and/or renewable raw materials. Copper in overhead electricity lines is being replaced by aluminium, a metallic ore whose availability is a thousand times greater.

But there are limits to substitution, the pessimists stress. What is the alternative for phosphates in agriculture? Phosphorus is a building stone of life. It is indispensable for plants, animals and man. Agriculture cannot feed seven billion people without adding phosphorus bonds (phosphate) to fields in the form of fertilisers. Virtually all fertiliser plants consume dwindling reserves of phosphate ore. Phosphate production could reach its peak this century, with the world’s population growing to eleven billion. Malthus could be right after all.

The precautionary principle

What would the planet-hoppers in Interstellar include in their generation contract about the use of non-renewable raw materials, now that the principle of sustainable development doesn’t yield a definite answer? As they will be the ones to experience the exhaustion of the Earth first-hand, there is a good chance they will revert to another principle in environmental law: the precautionary principle. This implies that in the case of scientific doubt, action is needed to remove the threat of irreversible damage. In short, the planet hoppers would tend to the position of the raw material pessimists. Better safe than sorry

The stock of each mineral in the exoplanet’s crust can be determined by using soil samples. As is the case on Earth, 0.01% of the reserves can be said to be suitable for mining. To prevent later generations from missing out, mining should be spread over the exoplanet’s life span – possibly billions of years. This requires, in the first place, the recycling of raw materials for as long as possible instead of allowing them to pollute the air, water or soil, and the allocation of the scarcest raw materials for the most essential industrial applications.

The planet-hoppers include the recycling of raw materials and the substitution principle in their generation contract. But even then there is the danger that a proportional distribution of minerals among all the conceivable generations would make slim pickings.

No licence

That is why, at this point in the deliberations, protests are beginning to be heard. Is the principle of proportionality not too rigid? Imagine you belong to the first generation to arrive on the exoplanet, some participants say, then you have the hardest job: rebuilding an economy and a civilisation. Even if the pioneers are few, they still need more raw materials for construction. Those belonging to the late-comers profit from the construction works. If our ancestors on Earth had restricted themselves in using copper and tin, they would never have emerged from the Stone Age. Life on Earth would have remained miserable and brief.

In this vision, the mining of raw materials does not mean that future generations are burgled, as long as natural capital is converted into alternative capital to be passed on to our descendants. Economic capital in the form of machines, buildings and an agricultural system to feed mankind; human capital in the form of knowledge and culture; social capital in the form of mutual trust; and institutional capital in the form of the bodies that protect our rights.

There can be no freedom without the fulfilment of basic needs and without human rights. Life would become miserable. An unfree society would kill the creativity needed to find solutions for scarcity – that is where the interests of later generations come into play. Counter-intuitively: if previous generations starved themselves under dictatorial rule in order to save raw materials for posterity, there is a greater chance of those generations to come starving as well. Intuitively: North Korea is not a model of sustainability.

The transformation of natural capital is no licence for the ongoing waste of raw materials. It is indefensible that we, in the industrialised world, consume twice as much phosphate – especially due to meat consumption – than our bodies need. Over-consumption goes counter to capital formation. What is defensible, however, is that 21st century generations, in order to make the transition from fossil to renewable energy at all possible, will mine a disproportionate number of rare metallic ores such as neodymium for the magnets in wind turbines. A clean supply of energy safeguards the security of all the generations to come.

If the planet-hoppers accept our thought experiment that in the development of man-made capital a larger claim on the exoplanet’s natural capital is justified, they have again moved in the direction of the raw material optimists with their emphasis on human inventiveness. Old Locke would approve of this: he submitted that the proviso of enough and as good can be cancelled out if everyone is better off under the new rules than under the old.


Behind their veil of ignorance, the planet-hoppers have arrived at an intergenerational version of philosopher John Rawls’ difference principle: inequality is permitted, but only if it benefits the weakest. This principle also applies to another issue the colonisers must solve: the division of raw materials within each generation. It is obvious that people, as they spread across the exoplanet, form different communities. If every community claims full ownership of the minerals in its soil, as countries on Earth do, this may result in high inequality. Communities with many raw materials have an undeserved advantage over communities with few resources. As this inequality affects later generations, they should be solved in the generation contract.

The issue occupies philosophers too. Thomas Pogge argues that natural resources belong to all of mankind. Although, he realises that you cannot entirely take away the say countries have over the minerals in their soil. In order to put right the inequality emanating from the unequal distribution of raw materials, he favours, with an appeal to Rawls, a Global Resources Dividend: a modest levy on the exploitation of raw materials, the proceeds of which are to be used to eradicate extreme poverty in the world.

Unfortunately, Pogge pushes the Lockean proviso aside. His levy will slacken the exploitation of raw materials somewhat, but doesn't guarantee that the world population of the future gets a fair share of these raw materials.

In order to be fair from both an international and an intergenerational perspective, an equalization mechanism will have to check the pace with which raw materials are mined. A system of tradeable mining quotas could yield such double fairness, provided it takes historical inequalities into account – for instance, having the rich countries pay for their quotas and granting the proceeds to poor countries. Such quotas are at odds, however, with the sovereign right of every country to exploit its own natural resources. This principle was even included in the 1992 UN Climate Treaty.

But as soon as our imaginary planet-hoppers leave Earth, they are no longer bound to this principle. So they dump it. In doing so, they create space to jointly set up a fair distribution of mineral resources between communities, one that does justice to their earlier understandings about the distribution among generations. It is conceivable that, at the end of their deliberations, they will conclude that the most disadvantaged communities and generations would benefit from a system of tradeable quotas.

The mining of copper for instance is then limited to what is justified with regard to future generations. The annual maximum is divided among all communities in the form of quotas. A community whose soil is devoid of copper ore can transfer its copper quota to a community wanting to mine more copper, in exchange for part of the copper mined. Ultimately, all the communities involved benefit from copper mining. Every community has the freedom not to exploit the raw materials in its soil, for example, because of the damage and the disruption caused by mining.

The tricky issue as to whom the minerals in the Earth’s crust belong to is solved by splitting up the concept of property: every community has a say in its mineral resources, but the limitations to the exploitation and the (re)division of the yields are an issue involving mankind at large.

Planet A

The thought experiment inspired by Interstellar yields a number of principles that lend themselves to a new social contract on non-renewable raw materials among generations, the starting-point being an equitable distribution of these raw materials among all the conceivable generations. If there is uncertainty about reserves suitable for mining, the precautionary principle is applied. Raw materials are not wasted, but kept in a cycle as long as possible (i.e. circular economy). The scarcest raw materials are replaced by less scarce ones (i.e. substitution).

Generations may take possession of a disproportionate part of a given raw material, provided they convert these into resources (i.e. capital) in order to safeguard the livelihood and freedom of later generations. The application of this difference principle is an exception to the proportionality principle which needs to be validated in each specific case. After all, human capital is of no use to later generations if there is no natural capital left.

In the distribution of raw materials within generations the difference principle applies: raw materials, at any rate their proceeds, will have to be divided in such a way that the community with the fewest raw materials consents.

There is no need to wait with the execution of this contract until we are forced to colonise new planets. Those who see space travel as the rescuer of mankind have seen too many sci-fi films. Then, the slogan of the green movement is more realistic: There is no planet B. Luckily, planet A can serve as a suitable habitat for mankind for another billion years, if we do not exhaust it all too rapidly.


Our generation contract stipulates that the last generations of people on Earth are entitled to a fair share in non-renewable raw materials as well. But can you expect people to recognise those living in a billion years from now as moral equals, claiming an equally large part of the Earth’s riches? Many would want to move on to an ethics of virtues (modesty, justice, respect for the Earth) rather than applying abstract rules of distribution. We then act morally if we take action personally, in cutting back on the use of raw materials, promoting it in our society and working towards a fair distribution of the proceeds of mining among the world’s population.

But it would be irresponsible to let go of the long-term perspective. It gives us better insight into which raw materials we have to be economical with. Solidarity with people living in a thousand years – that’s roughly forty generations – is that asking too much? If we want metallic ores to be available to them still, we have to cut back on our use of (newly-mined) antimony by an estimated 99%, as the above-mentioned Utrecht researchers have calculated.

For molybdenum (96%), zinc (95%) and fourteen other metals (more than 50%), they also arrive at substantial reduction percentages. The mining of phosphate ore will have to be scaled down substantially as well, and existing reserves distributed more equally. A daunting, but attainable, task.

The Dutch version of this article appeared in De Helling, Summer 2015. It has been translated into English for the website of the Green European Journal.



  • Eric Hees, Voedsel, grondstoffen en geopolitiek, CLM, 2013.
  • Henckens, P. Driessen and E. Worrell (Universiteit Utrecht), ‘Metal scarcity and sustainability, analyzing the necessity to reduce the extraction of scarce metals’, in: Resources, Conservation and Recycling 93, 2014.
  • Christopher Nolan (director), Interstellar, 2014.
  • Thomas Pogge, World Poverty and Human Rights, 2008 (2002).
  • John Rawls, A Theory of Justice, 1999 (1971).
  • Socrates Schouten, De circulaire economie. Waarom productie, consumptie en groei fundamenteel anders moeten, Leesmagazijn, 2015.
  • Kip Thorne, The Science of Interstellar, 2014.
  • WRR, Naar een lerende economie. Investeren in het verdienvermogen van Nederland, 2014.