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There are many ethical decisions that human beings make with respect to the environment. For example:
- Should humans continue to clear cut forests for the sake of human consumption?
- Why should humans continue to propagate its species, and life itself? 
- Should humans continue to make gasoline-powered vehicles?
- What environmental obligations do humans need to keep for future generations?
- Is it right for humans to knowingly cause the extinction of a species for the convenience of humanity?
- How should humans best use and conserve the space environment to secure and expand life?
- What role can Planetary Boundaries play in reshaping the human-earth relationship?
The academic field of environmental ethics grew up in response to the works of Rachel Carson and Murray Bookchin and events such as the first Earth Day in 1970, when environmentalists started urging philosophers to consider the philosophical aspects of environmental problems. Two papers published in Science had a crucial impact: Lynn White's "The Historical Roots of our Ecologic Crisis" (March 1967) and Garrett Hardin's "The Tragedy of the Commons" (December 1968). Also influential was Garett Hardin's later essay called "Exploring New Ethics for Survival", as well as an essay by Aldo Leopold in his A Sand County Almanac, called "The Land Ethic", in which Leopold explicitly claimed that the roots of the ecological crisis were philosophical (1949).
The first international academic journals in this field emerged from North America in the late 1970s and early 1980s – the US-based journal
Some scholars have tried to categorise the various ways the natural environment is valued.
Marshall's libertarian extension echoes a civil liberty approach (i.e. a commitment to extending equal rights to all members of a community). In environmentalism, the community is generally thought to consist of non-humans as well as humans.
Andrew Brennan was an advocate of ecologic humanism (eco-humanism), the argument that all ontological entities, animate and inanimate, can be given ethical worth purely on the basis that they exist. The work of Arne Næss and his collaborator Sessions also falls under the libertarian extension, although they preferred the term "deep ecology". Deep ecology is the argument for the intrinsic value or inherent worth of the environment – the view that it is valuable in itself. Their argument falls under both the libertarian extension and the ecologic extension.
Peter Singer's work can be categorized under Marshall's 'libertarian extension'. He reasoned that the "expanding circle of moral worth" should be redrawn to include the rights of non-human animals, and to not do so would be guilty of speciesism. Singer found it difficult to accept the argument from intrinsic worth of a-biotic or "non-sentient" (non-conscious) entities, and concluded in his first edition of "Practical Ethics" that they should not be included in the expanding circle of moral worth. This approach is essentially then, bio-centric. However, in a later edition of Practical Ethics after the work of Næss and Sessions, Singer admits that, although unconvinced by deep ecology, the argument from intrinsic value of non-sentient entities is plausible, but at best problematic. Singer advocated a humanist ethics.
Alan Marshall's category of ecologic extension places emphasis not on human rights but on the recognition of the fundamental interdependence of all biological (and some abiological) entities and their essential diversity. Whereas Libertarian Extension can be thought of as flowing from a political reflection of the natural world, ecologic extension is best thought of as a scientific reflection of the natural world. Ecological Extension is roughly the same classification of Smith's eco-holism, and it argues for the intrinsic value inherent in collective ecological entities like ecosystems or the global environment as a whole entity. Holmes Rolston, among others, has taken this approach.
This category might include James Lovelock's Gaia hypothesis; the theory that the planet earth alters its geo-physiological structure over time in order to ensure the continuation of an equilibrium of evolving organic and inorganic matter. The planet is characterized as a unified, holistic entity with ethical worth of which the human race is of no particular significance in the long run.
Marshall's category of 'conservation ethics' is an extension of use-value into the non-human biological world. It focuses only on the worth of the environment in terms of its utility or usefulness to humans. It contrasts the intrinsic value ideas of 'deep ecology,' hence is often referred to as 'shallow ecology,' and generally argues for the preservation of the environment on the basis that it has extrinsic value – instrumental to the welfare of human beings. Conservation is therefore a means to an end and purely concerned with mankind and inter-generational considerations. It could be argued that it is this ethic that formed the underlying arguments proposed by Governments at the Kyoto summit in 1997 and three agreements reached in the Rio Earth Summit in 1992.
Peter Singer advocated the preservation of "world heritage sites", unspoilt parts of the world that acquire a "scarcity value" as they diminish over time. Their preservation is a bequest for future generations as they have been inherited from human's ancestors and should be passed down to future generations so they can have the opportunity to decide whether to enjoy unspoilt countryside or an entirely urban landscape. A good example of a world heritage site would be the tropical rainforest, a very specialist ecosystem that has taken centuries to evolve. Clearing the rainforest for farmland often fails due to soil conditions, and once disturbed, can take thousands of years to regenerate.
The Christian world view sees the universe as created by God, and humankind accountable to God for the use of the resources entrusted to humankind. Ultimate values are seen in the light of being valuable to God. This applies both in breadth of scope – caring for people (Matthew 25) and environmental issues, e.g. environmental health (Deuteronomy 22.8; 23.12-14) – and dynamic motivation, the love of Christ controlling (2 Corinthians 5.14f) and dealing with the underlying spiritual disease of sin, which shows itself in selfishness and thoughtlessness. In many countries this relationship of accountability is symbolised at harvest thanksgiving. (B.T. Adeney : Global Ethics in New Dictionary of Christian Ethics and Pastoral Theology 1995 Leicester)
Abrahamic religious scholars have used theology to motivate the public. John L. O'Sullivan, who coined the term manifest destiny, and other influential people like him used Abrahamic ideologies to encourage action. These religious scholars, columnists and politicians historically have used these ideas and continue to do so to justify the consumptive tendencies of a young America around the time of the Industrial Revolution. In order to solidify the understanding that God had intended for humankind to use earths natural resources, environmental writers and religious scholars alike proclaimed that humans are separate from nature, on a higher order. Those that may critique this point of view may ask the same question that John Muir asks ironically in a section of his novel A Thousand Mile Walk to the Gulf, why are there so many dangers in the natural world in the form of poisonous plants, animals and natural disasters, The answer is that those creatures are a result of Adam and Eve's sins in the garden of Eden.
Since the turn of the 20th century, the application of theology in environmentalism diverged into two schools of thought. The first system of understanding holds religion as the basis of environmental stewardship. The second sees the use of theology as a means to rationalize the unmanaged consumptions of natural resources. Lynn White and Calvin DeWitt represent each side of this dichotomy.
John Muir personified nature as an inviting place away from the loudness of urban centers. "For Muir and the growing number of Americans who shared his views, Satan's home had become God's Own Temple." The use of Abrahamic religious allusions assisted Muir and the Sierra Club to create support for some of the first public nature preserves.
Authors like Terry Tempest Williams as well as John Muir build on the idea that "...God can be found wherever you are, especially outside. Family worship was not just relegated to Sunday in a chapel." References like these assist the general public to make a connection between paintings done at the Hudson River School, Ansel Adams' photographs, along with other types of media, and their religion or spirituality. Placing intrinsic value upon nature through theology is a fundamental idea of deep ecology.
Normative ethical theories
Normative ethics is a field in Moral Philosophy that investigates how one ought to act. What is morally right and wrong, and how moral standards are determined. Superficially, this approach may seem intrinsically anthropocentric. However, theoretical frameworks from traditional normative ethical theories are abundant within contemporary environmental ethics.
Consequentialist theories focus on the consequences of actions, this emphasises not what is 'right', but rather what is of 'value' and 'good'. Act Utilitarianism, for example, expands this formulation to emphasise that what makes an action right is whether it maximises well-being and reduces pain. Thus, actions that result in greater well-being are considered obligatory and permissible. It has been noted that this is an 'instrumentalist' position towards the environment, and as such not fully adequate to the delicate demands of ecological diversity.
Aldo Leopold's Land Ethic (1949) tries to avoid this type of instrumentalism by proposing a more holistic approach to the relationship between humans and their 'biotic community', so to create a 'limit' based on the maxim that "a thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community; it is wrong when it tends otherwise." Thus, the use of natural resources is permissible as long as it does not disrupt the stability of the ecosystem. Some philosophers have categorised Leopold's views to be within a consequentialist framework, however it is disputed whether this was intentional. Other consequentialist views such as that of Peter Singer tend to emphasise the inclusion of non-human sentient beings into ethical considerations. This view argues that all sentient creates which are by nature able to feel pleasure and pain, are of equal moral consideration for their intrinsic value. Nevertheless, non-sentient beings, such as plants, rivers and ecosystems, are considered to be merely instrumental.
Theories of rights, for example, are generally deontological. That is, within this framework an environmental policy that gives rights to non-human sentient beings, would prioritise the conservation of such in their natural state, rather than in an artificial manner. Consider for example, issues in climate engineering; Ocean fertilisation aims to expand marine algae in order to remove higher levels of CO2. A complication from this approach is that it creates salient disruptions to local ecosystems. Furthermore, an environmental ethical theory based on the rights of marine animals in those ecosystems, would create a protection against this type of intervention. Environmental deontologists such as Paul W. Taylor, for example, have argued for a Kantian approach to issues of this kind. Taylor argues that all living things are 'teleological centres of life'  deserving of rights and respect. His view uses a concept of 'universalizability', to argue that one ought to act only on actions which could be rationally willed as a universal law. Val Plumwood has criticised this approach by noting that the universalisation framework, is not necessarily based on 'respect' for the other, as it's based on duty and 'becoming' part of the environment.
Virtue ethics states that some behaviours should be cultivated, and others avoided. This framework avoids problems of defining what is of intrinsic value, by instead arguing that what is important is to act in accordance with the correct balance of virtue. The Golden mean formulation, for example, states that to be 'generous' (virtue), one should neither be miserly (deficiency) or extravagant (excess). Unlike deontology and consequentialism, theories of virtue focus their formulations on how the individual has to act to live a flourishing life. This presents a 'subjective flexibility' which seems like an adequate position to hold considering the fluctuating demands of sustainability. However, as a consequence, it can also be said that this is an inherently anthropocentric standpoint.
Some Ecofeminist theories such as that of Val Plumwood, have been categorised as a form of virtue ethics. Plumwood argues that a virtue-based ethical framework adapts more fittingly to environmental diversity, as virtues such as 'respect', 'gratitude', and 'sensitivity', are not only suitable to ecological subjectivity but also more applicable to the views of indigenous people. Furthermore, what traits would be considered as part of environmental vices? Ronald Sandler argues that detrimental dispositions to human flourishing such as 'greed', 'intemperance' and 'arrogance', lead to detrimental dispositions to the protection of the environment such as 'apathy', against other species, and 'pessimism' about conservation. Views such as this, create a mutualistic connection between virtuous human flourishing, and environmental flourishing.
Anthropocentrism is the position that humans are the most important or critical element in any given situation; that the human race must always be its own primary concern. Detractors of anthropocentrism argue that the Western tradition biases homo sapiens when considering the environmental ethics of a situation and that humans evaluate their environment or other organisms in terms of the utility for them (see speciesism). Many argue that all environmental studies should include an assessment of the intrinsic value of non-human beings, which would entail a reassessment of humans ecocultural identities. In fact, based on this very assumption, a philosophical article has explored recently the possibility of humans' willing extinction as a gesture toward other beings. The authors refer to the idea as a thought experiment that should not be understood as a call for action.
Baruch Spinoza reasoned that if humans were to look at things objectively, they would discover that everything in the universe has a unique value. Likewise, it is possible that a human-centred or anthropocentric/androcentric ethic is not an accurate depiction of reality, and there is a bigger picture that humans may or may not be able to understand from a human perspective.
Peter Vardy distinguished between two types of anthropocentrism. A strong anthropocentric ethic argues that humans are at the center of reality and it is right for them to be so. Weak anthropocentrism, however, argues that reality can only be interpreted from a human point of view, thus humans have to be at the centre of reality as they see it.
Another point of view has been developed by Bryan Norton, who has become one of the essential actors of environmental ethics by launching environmental pragmatism, now one of its leading trends. Environmental pragmatism refuses to take a stance in disputes between defenders of anthropocentrist and non-anthropocentrist ethics. Instead, Norton distinguishes between strong anthropocentrism and weak-or-extended-anthropocentrism and argues that the former must underestimate the diversity of instrumental values humans may derive from the natural world.
A recent view relates anthropocentrism to the future of life. Biotic ethics are based on the human identity as part of gene/protein organic life whose effective purpose is self-propagation. This implies a human purpose to secure and propagate life. Humans are central because only they can secure life beyond the duration of the Sun, possibly for trillions of eons. Biotic ethics values life itself, as embodied in biological structures and processes. Humans are special because they can secure the future of life on cosmological scales. In particular, humans can continue sentient life that enjoys its existence, adding further motivation to propagate life. Humans can secure the future of life, and this future can give human existence a cosmic purpose.
Status of the field
Only after 1990 did the field gain institutional recognition at programs such as Colorado State University, the University of Montana, Bowling Green State University, and the University of North Texas. In 1991, Schumacher College of Dartington, England, was founded and now provides an MSc in Holistic Science.
These programs began to offer a master's degree with a specialty in environmental ethics/philosophy. Beginning in 2005 the Department of Philosophy and Religion Studies at the University of North Texas offered a PhD program with a concentration in environmental ethics/philosophy.
In Germany, the University of Greifswald has recently established an international program in Landscape Ecology & Nature Conservation with a strong focus on environmental ethics. In 2009, the University of Munich and Deutsches Museum founded the Rachel Carson Center for Environment and Society, an international, interdisciplinary center for research and education in the environmental humanities.