Two papers published in Science had a crucial impact: Lynn White's "The Historical Roots of our Ecologic Crisis" (March 1967)[8] and Garrett Hardin's "The Tragedy of the Commons" (December 1968).
[12] Marshall's libertarian extension echoes a civil liberty approach (i.e. a commitment to extending equal rights to all members of a community).
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".
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.
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.
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 independent ethical value, compared to which the human race is of no particular significance in the long run.
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.
"[17] The use of Abrahamic religious allusions assisted Muir and the Sierra Club to create support for some of the first public nature preserves.
"[18] 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.
Act Utilitarianism, for example, expands this formulation to emphasize that what makes an action right is whether it maximises well-being and reduces pain.
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.
In strong contrast to consequentialism, this view argues for principles of duty based not on a function of value, but on reasons that make no substantive reference to the consequences of an action.
[24] Thus, if the natural environment is categorised as intrinsically valuable, any destruction or damage to such would be considered wrong as a whole rather than merely due to a calculated loss of net value.
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.
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 character trait.
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.
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,[31] which would entail a reassessment of humans ecocultural identities.
[32] 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.
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.
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.