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The Ethics of Terraforming

Terraforming is the artificial transformation of other planets into places suitable for human habitation. A good thing, surely? Paul York argues that terraforming isn’t as ethically straightforward as you might think.

“Terraforming is a process of planetary engineering, specifically directed at enhancing the capacity of an extraterrestrial planetary environment to support life. The ultimate in terraforming would be to create an uncontained planetary biosphere emulating all the functions of the biosphere of the Earth – one that would be fully habitable for human beings”

(M.J.Fogg, Terraforming, 1995, pp.89-90).

Terraforming is essentially ‘eco-engineering’ on a planetary scale. One takes, for example, a ‘dead’, airless, dry, frigid, planet like Mars and takes steps to generate and retain a breathable atmosphere, produce liquid water, and raise the temperature to an appropriate level. Plants can then be grown, animals and human beings will be able to live there and eventually the planet will become self-sufficient with its own habitations and civilization.

In practical terms, terraforming Mars would involve at least the following: artificial melting of the Martian polar caps and/or the permafrost to produce liquid water and gaseous carbon dioxide, in the process increasing the surface temperature of the planet; and artificial production of gases to raise atmospheric pressure and temperature and to protect introduced life forms from UV radiation. By any standards, this would be a massive undertaking, greater by many orders of magnitude than any engineering effort ever undertaken by human beings.

One particular approach to terraforming Mars, known as the Runaway Greenhouse Effect, is described by Martyn Fogg (1995, p.5) as “a catastrophic climatic instability caused by the release of greenhouse gases (e.g water vapour and CO2) from artificially heated surface reservoirs into a planetary atmosphere. This heats the planetary surface, releasing more gas and so on until the climate ‘runs away’ in a positive feedback cycle to some stable, high-temperature regime.”

This approach raises a number of interesting points. First, the methods employed for releasing greenhouse gases from the Martian crust will depend on the quantity of gases locked in or near the surface and also on the manner of their chemical combination with or storage in the rocks of the crust. For example, whilst it may be possible to release water vapour and gases from surface rocks and permafrost through the direct application of heat focussed by huge solar mirrors positioned nearby in space, it may be necessary to detonate nuclear devices to directly release water stored in underground aquifers or to generate sufficient heat to release water from the permafrost. Clearly, some terraforming approaches may be more acceptable than others.

Second, the ‘stable, high-temperature regime’ referred to had better not just be any old regime. For the planet to be habitable, the mean surface temperature of Mars would need to be raised from around -56ºC and then stabilized within some fairly narrow band around 15ºC, which is the mean surface temperature of the Earth. Approaches of this kind are not lightly called ‘runaway’, as the mean surface temperature of Venus is of the order of 460ºC, a situation widely thought to be due to natural greenhouse effects. Achieving the desired temperature target would not necessarily be a straightforward matter.

Sounds Like Science Fiction!

It does rather. In fact, the very first mention of terraforming was in a story called ‘Collision Orbit’ by Jack Williamson (using the pseudonym Will Stewart), published in the July 1942 issue of Astounding Science Fiction magazine. However, terraforming is potentially more real than you might think…

We currently have the technology to launch astronauts to Mars and return them safely to Earth. It would appear that we also have the technology and the capacity to establish a permanent, manned scientific base on Mars. Indeed, in 1989 on the 20th anniversary of Apollo 11, then-President George Bush announced the Space Exploration Initiative or SEI, calling it “a new vision for America in the 21st century – a vision that will return us to the Moon to stay, and onwards to Mars by 2019.”

NASA has since cancelled the SEI, in response to political and funding pressures, and now the immediate priorities of the Agency are to complete the International Space Station and to develop next-generation launch capabilities. Nonetheless, NASA’s current priorities are clearly steppingstones along the way to a manned Mars mission, a mission that could be re-activated at any time, for example as a means of re-focussing the attention of the American people (in the wake of September 11) on something other than the threat of terrorism, and giving them a renewed sense of purpose in an insecure world.

Many of the supporters of a Mars manned mission see it as a natural precursor to a permanent human presence on the planet. Indeed, there is a strong view that Mars can legiti-mately be seen as a potential new home for human kind – a new frontier, and that it is a natural step in human history and achievement that the planet Mars be colonised (Zubrin, 1996). For settlement to occur on any significant scale, it is likely that Mars would need to be terraformed first.


While at first sight it might seem as though human beings ought to be able to do whatever they like with a ‘dead’ planet , I will argue that it is by no means a straightforward ethical matter, and may even be morally wrong – a massive act of vandalism, in fact.

OK, So What’s Wrong With Terraforming?

Most people would probably think there is nothing wrong with terraforming, and they are in good company, as lots of philosophers would agree with them. The commonsense view is that terraforming an extraterrestrial planet would be a perfectly ethical thing to do, social and economic considerations permitting.

This is actually in complete accord with our orthodox ethical framework. A widespread view among ethicists today is that the moral community consists of rational ‘moral agents’ (persons) and ‘moral patients’, those members of the moral community who can be affected by moral agents. Note that people can be both moral agents and moral patients simultaneously. Ethics seeks to clarify the sorts of actions that are permissible, obligatory, or prohibited on the part of moral agents.

For a long time, the set of moral patients was coextensive with the set of moral agents (persons). More recently, there has been an expansion of the moral community to acknowledge the ‘moral considerability’ of other entities beside persons: first, higher animals, then all sentient beings, and then (according to some philosophers, at least) all living things. Note that in this expanded moral community, persons are still the only moral agents.

There are three things to notice about this framework: firstly, if you are a member of the moral community, then you are considered in the process of ethical decision-making according to your moral significance; secondly, if you are not part of the moral community, then you are simply not considered in the process of ethical decision-making, and thirdly, the overwhelming majority of entities in the universe are not, in fact, regarded as part of the moral community – they are not ‘morally considerable’.

Mountains, rivers, rocks, planets, stars, galaxies and all manner of artifacts are excluded. Only if they are implicated in some biota (a biota is a habitat for life such as a river or a coral reef) are they regarded as morally significant, because of their instrumental value in supporting life. In particular, this means that Mars (being lifeless) is not regarded as being ‘morally considerable’, and so, according to our orthodox ethical framework, there would be nothing wrong with terraforming Mars.

We have been able to get by with such an impoverished ethical framework because, as Christopher McKay (1990, p.186) says, up until now “virtually all of the serious considerations of environmental ethics have been embedded within the context of the Earth …” with its all-pervasive life. So,

The recognized global interconnection of life through the biogeochemical cycles prevents one from rigorously treating any single object or collection of inanimate objects independently from the biological perspective. Thus the extension of rights from life to ‘mere things’ may have no practical implications on Earth (McKay, 1990, p.195).

In other words, because virtually all non-biological entities on Earth are implicated in the biota somehow, we simply have never had to consider their value apart from their biological supporting role. The implications are twofold: firstly, that there may after all be intrinsic, non-instrumental value in non-biological entities once we learn to see it and, secondly, that in extraterrestrial environments at least, we may soon have to begin to acknowledge this. If such entities are to receive their due, they will need to be included in the moral community.

In fact, very few philosophers have been prepared to take this additional step and include non-living entities in the moral community, but this is precisely what I wish to do in pursuit of a ‘cosmocentric ethics’ – an ethics that regards all entities as being morally considerable, though not necessarily of equal moral significance. The ‘commonsense’ view has a very long history, going back at least as far as Genesis 1:27-28: “…God created man in his own image… and God said … ‘fill the earth and subdue it; have dominion over the fish of the sea, over the birds of the air, and over every living thing that moves on the earth.’” It is but a small step from here to the egregious view that humankind is the legitimate master (or God’s steward) of the entire universe.

One argument often used in favour of terraforming is that we should settle another planet (Mars) so that human civilization has a backup planet in case something should happen to the Earth. There are three common scenarios:

1. Humanity ruins or pollutes the Earth so that it is no longer habitable.

Response: I suggest that any species that wrecks its home environment would also be a very poor long-term proposition for any new home planet. Should we settle Mars soon, two things could well happen. Firstly, having a second home on Mars may effectively remove any incentive for solving Earth’s problems – we can always pollute the Earth, secure in the knowledge that there is an alternative home, should Earth become uninhabitable. Secondly, since we have not yet learned how to manage the Earth, there is a good chance that Mars could end up ruined as well.

2. Earth is destroyed through no fault of ours, for example, as a result of a major meteorite strike like the one that apparently wiped out the dinosaurs some 65 million years ago.

Response: Whilst a reasonable argument at first glance, I suspect that other measures to future-proof the human race against such an eventuality (for example by constructing a few self-sustaining, underground colonies on Earth, or by taking steps to detect and deal with incoming meteors) would be orders of magnitude less expensive than colonizing Mars. Indeed, a number of projects of this kind – for example, NASA’s Near-Earth Asteroid Tracking (NEAT) programme – are already in place.

3. Earth eventually becomes uninhabitable in the natural course of things, as the Sun evolves into a red giant, expanding in diameter out towards the Earth’s orbit, making the Earth too hot to support life (eventually the oceans will boil) and possibly burning it to a cinder.

Response: Consider the timeframes involved. The Sun is likely to remain stable for another five billion years before it begins to seriously ‘misbehave’. By contrast Homo sapiens has occupied the Earth for ‘only’ 100,000 years or so – this is only 1/10,000th of the Earth’s remaining lifespan. Clearly, we have time on our side and there is absolutely no need to rush to Mars – some scenarios require as little as 600 years to achieve a limited habitable environment.

So, these arguments aren’t very convincing. The real motivation for terraforming, I suspect, is more likely to be along the lines of the following quote from the chief engineer of Lockheed Martin, Robert Zubrin (1996, p.248-9):

Mars may someday provide a home for a dynamic new branch of human civilization, a new frontier, whose settlement and growth will provide an engine of progress for all of humanity for generations to come.

Zubrin is clearly extolling the virtues of pioneering, development, and economic growth, a set of values that is deeply implicated in the Earth’s current environmental problems. Later in his book, he makes no secret of where he stands: “I would say that failure to terraform Mars constitutes failure to live up to our human nature and a betrayal of our responsibility as members of the community of life itself” [italics his].

Why I Think Terraforming is Ethically Questionable…

Mars, the Red Planet, is a beautiful and interesting place in its own right. It has magnificent canyons (Valles Marineris is longer than any canyon on Earth) and soaring extinct volcanoes (Olympus Mons is 26 kilometres high), together with beautifully-sculpted white polar caps containing frozen water and carbon dioxide, and a great variety of cratered and geologically-layered terrain. Mars has seasons and its own weather system – high white clouds, ground mists and frosts, and planet-wide dust storms that last for months. Terraforming would, of necessity, change or destroy much of this.

Although Mars harbours no life forms of any kind, as far as we know, it has significant intrinsic value – a value that exists irrespective of any value that humanity may place on it.

Most philosophers would disagree, saying that whilst human beings have intrinsic value, almost everything else (animals, plants, insects, geological formations, rocks, ecosystems, the planet Mars) only has whatever value is placed on it by human beings – in other words, extrinsic value. For example, a human being might regard a particular thing as having value because it performs some useful function, say a rock that acts as a paperweight (instrumental value) – such entities have no value of their own. In the mainstream view, if a thing is not of value to some person, then it has no value at all, period.

J.B.Callicott (1986, p.142) draws a useful distinction between the source and the locus of values. So whilst humanity may be the source of all values, it is not necessarily the locus of all values, especially that value which resides in the thing itself, of which particular valuations (by people) merely reflect different perceptions of the thing (and its intrinsic value) – “intrinsic values are not imposed by human beings; they merely involve human recognition of value” (Marshall, 1993, p.233).

Some thinkers argue that we should widen the moral community by including entities other than human beings, for example the ‘higher’ animals, sentient beings, living things or perhaps even ecosystems. Sometimes the rationale is that these other entities have intrinsic value; at other times it is argued that these entities deserve inclusion because they are capable of being harmed or benefited by moral agents, or that they have instrumental value in supporting life (for example, a coral reef).

Keekok Lee (1994, p.92) argues that we should go further still, beyond the biocentric view, and “develop a conception of intrinsic value which is not necessarily tied up solely with the fate of biotic Nature … [and] confront the issue of abiotic or inanimate nature as a locus of intrinsic value”. His approach is to start by constructing an ‘intrinsic value ethics’ for the Earth (with a view to later extending it to Mars) based on the following considerations. Firstly, Earth did not come into existence (or continue to exist) for the benefit of human beings. Secondly, although human beings find much of nonbiological Nature useful, it doesn’t follow that Nature exists for humanity. Expanding on this, he points out that: a) the genesis of the Earth is independent of the arrival of humans; b) Earth and its biota would not be extinguished if humanity were to become extinct; c) the functioning of the biota as a systemic whole would be independent of humans; d) Earth and its biosphere are autonomous; and e) from the perspective of Earth and its biota, humanity is dispensable and maybe even redundant.

Such considerations highlight the extreme asymmetry in causal dependence between humans and Nature, inasmuch as we depend entirely on Nature whereas the reverse clearly isn’t at all the case. This makes our current ethical systems seem unduly anthropocentric and Earth-based.

Because of its intrinsic value, I would argue that Mars deserves moral consideration from rational moral agents (that is, human beings) – and it is precisely this that terraforming advocates fail to acknowledge. Thus, all else being equal, Mars is entitled to continue to exist in its present form, undisturbed by human attempts change it, whether directly or as a by-product of economic ‘development’. Granted that Mars has moral considerability, it is no longer a foregone conclusion that it is simply ‘there for the taking’. Activities that are and are not to be permitted on Mars must be decided via some moral calculus that weighs up the competing claims of Mars and humanity.

The above considerations regarding an ‘intrinsic value ethics’ show, says Lee, that “human arrogance and superiority toward Nature are misplaced” and that the appropriate attitude for us to take is one of awe and humility, maintaining “a respectful distance” from it. Whilst I concur wholeheartedly, it is important to stress that maintaining a ‘respectful distance’ from Nature does not necessarily entail a total lack of engagement with it. Indeed, I would contend that the exploration of Mars in no way implies disrespect and is, in fact, necessary to understand what Mars is – a prerequisite for any meaningful relationship or engagement with the planet.

If you are happy to grant moral considerability to living things, then Alan Marshall (1993, p.234) suggests that ‘living’ might not automatically imply ‘biological’: “It must be remembered that nature is not static in abiotic worlds. Myriads of dynamic physical, chemical and geological phenomena permeate lifeless planets.” The atmosphere of Jupiter with its cyclonic Great Red Spot, the volcanically active Jovian moon Io, or indeed the surface and atmosphere of Mars “could fulfil many definitions of what it is to be alive.”

Another philosopher, Robert Sparrow (1999, p.227-236) argues that terraforming “demonstrates at least two serious defects of moral character: an aesthetic insensitivity and the sin of hubris … to change whole planets to suit our ends is arrogant vandalism.” He claims that we can demonstrate aesthetic insensitivity in two ways: firstly, by destroying beauty directly and, secondly, by using beauty “for one’s own purposes in ways that make no reference to its beauty” even though that beauty is not destroyed.

Sparrow says “classically, hubris involves glorying in one’s own powers, a false optimism about them, and a haste to put them to the test. A lack of self-knowledge and self-reflection is also characteristic … as is a dismissive attitude toward both critics and past failures.” Sounds like terraforming?


In a cosmocentric ethics, moral reckoning would no longer be a straightforward matter. Moral considerability is not the same as moral significance. Just because an entity is admitted to moral consideration (or the moral community), by ascribing to it an intrinsic value, it does not automatically follow that it will have the same moral significance as other members of the moral community, such as human beings.

We will also need to develop some kind of ‘moral calculus’ that will allow us to balance the rights of the various entities – for example, a method for weighing up the right of a stone to exist against the rights of a human being, should these two rights be in conflict.

Robert Haynes (1990, p.177) argues that terraforming raises new issues in ethics, so that “we need from philosophers a new ‘cosmocentric’ ethics, and perhaps a revised theory of intrinsic worth … [Such a] cosmocentric ethic would allow scope for human creativity in science and engineering throughout the solar system” and also recognize that human artifacts are as much a part of the universe as natural objects like trees, planets, stars and animals. It is precisely such a cosmocentric ethics that I am advocating in this article.

© Paul York 2002

Paul York is an information systems architect. He has an MA in philosophy and is working on a PhD on the ethics of terraforming, at the University of Queensland, Australia.

Finding out more

• Callicott, J.B. (1986). ‘On the intrinsic value of non-human species’. The preservation of species: The value of biological diversity. B. Norton. Princeton Univ. Press.

• Fogg, M.J. (1995). Terraforming: engineering planetary environments. Society of Automotive Engineers.

• Haynes, R.H. (1990). ‘Ecce ecopoiesis: playing God on Mars’. Moral expertise. D. MacNiven. Routledge.

• Lee, K. (1994). ‘Awe and humility: Intrinsic value in nature – beyond an earthbound environmental ethics’. Philosophy and the natural environment. R. Attfield and A. Belsey. Cambridge Univ. Press.

• Marshall, A. (1993). ‘Ethics and the extraterrestrial environment’ Journal of Applied Philosophy.

• McKay, C.P. (1990). ‘Does Mars have rights? An approach to the environmental ethics of planetary engineering’. Moral Expertise. D.MacNiven. Routledge.

• Sparrow, R. (1999). ‘The ethics of terraforming’ Environmental Ethicsvol. 21.

• Zubrin, R. (1996). The case for Mars: the plan to settle the Red Planet and why we must. The Free Press.


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