Why should we value the earth and the environment? According to anthropocentrism, the environment has instrumental value to humans and should therefore be protected. According to biocentrism, nature should be protected because it has intrinsic value.
Biocentrism aims to be intuitive in claiming nature is always valuable. According to Onora O'Neill, this idea has an important problem. Primarily, biocentrism is a form of value realism. Nature can only have value if “value” is anything real and perceivable in the world. Establishing value realism is then a precursor to biocentrism. Since this is not done (according to O'Neill) biocentrism falls flat.
Under the umbrella term of anthropocentric ethics we have utilitairianism. In utilitairianism, we ought to strive for the greatest happiness for the greatest number. Non-human agents might not be able to experience pleasure or pain, leaving them out of equation. If we can prove that nature gives us pleasure, then we ought to protect nature. However, we do encounter trade-off situations, where an action that gives us great pleasure while destroying the environment is not only permissible.
Instead of focusing on the outcome, we can also focus on intention when determining the moral worth of a decision. By doing so, we avoid trade-off scenarios. However, these systems rely on extending (human) rights to non-human objects and agents. This leads us to the difficult world of animal rights which are notoriously hard to establish.
An alternative act-oriented approach is an obligation based approach. Obligations must be universalizable in such a system because we look for fundamental obligations. These obligations stem from our rational nature. Starting from fundamental obligation we can derive further (non-universal) obligations.