All persons ought to act so as to maximize value in general, which would include the value of all life over the long run.
This formulation of what I call the ecological axiom recognizes that value is inherent in all experience and thus all life. It incoporates insight from the thought of John B. Cobb Jr. who suggests considering the following alternatives as possible ethical principles from which to inform and guide our decision making and action:
1. So act as to maximize value for yourself in the present.
2. So act as to maximize value for yourself for the rest of your life.
3. So act as to maximize value for all human beings for the indefinite future.
4. So act as to maximize value in general (John B. Cobb, Jr., “Beyond Anthopocentrism in Ethics and Religion,” in On the Fifth Day, edited by R. Morris and Michael Fox. Washington D.C.: Acropolis Books, 1978, pp. 137-153).
Options one and two are not appropriate responses to the challenges of our time (or to the challenges of any time for that matter). The third principle is certainly more inclusive in that it includes the value of all human beings (and if we actually followed this principle it would be an improvement over our current course of action), but it ignores the intrinsic value of all life. Only the fourth alternative of maximizing value in general is appropriate for an adequate ecological ethic that recognizes the intrinsic value of all life. If the idea that value is connected to experience were accepted, this fourth alternative would entail maximizing the enjoyment of experience in general. Acting on such a principle would improve the quality of life of the human community and the ecological community of which we are a part.
The ecological axiom does not provide absolute moral principles to guide our decision-making and actions. The axiom must be applied contextually. Applying such a guiding principle to our decision making and actions requires complex analysis of the changing ecological situation and the interrelationships of the varying parts of the biosphere. The ecological axiom provides a general direction for action and social policy in our attempts to live in a sustainable relationship within our ecological community.
By balancing and harmonizing human and non-human values, we contribute to the health and enjoyment of all members of the biosphere. As the ecological axiom suggests, the maximizing of value in general, i.e., the maximization of sustainable enjoyment of all experients, ought to be accomplished with a view to the long run. Maximization of value in general in the present of even near future might lead to unsustainable practices in relation to future generations of experients. If value of in general is to be maximized, the value of future experients ought also to be considered.
One World House - Mark Davies 
For a somewhat more nuts & bolts version of the above discussion, I heartily recommend reading Stewart Brand’s _Whole Earth Discipline_. In it, he points out that it is too late to just “Do no harm”, we must actively begin to manage and repair our exploited ecologies.
In my own opinion, I would comment on the use of the word “act” in these ethical meditations. Does that word, in practice, not actually mean “act, while not giving offense, … “, which in most cases comes to mean forming one’s private opinion, being satisfied with it and it’s ethicality, and actually not doing much of anything?
Preserving a livable environment for future generations will not be accomplished quietly. It is already too late for the rest of this century. The question is whether, in the 2200s, we can get back to the climate of the 1900s.