Does Darwin's view of reality instill optimism or pessimism at the prospect of solving environmental problems?
I think that any discussion of the ethical implications of Darwin is going to be complex and something in which there is something for all sides. Darwin deliberately left alone the discussion of ethics that arise out of his theoretical foundations. Perhaps, he understood the profound level of questioning and almost infinite regression that would emerge as a result.
Certainly, a case can be made for the Darwinian "survival of the fittest" thought that would inspire a sense of pessimism for solving environmental problems. In this line of logic, Darwin's construction of human nature, his view of reality, is one in which human beings use what they can, when they can, for whatever use. There is no real and substantive notion of either conservation or redemption. Rather, there is a downward progression of "use or lose." In this configuration, one that demands short term immediacy over long term planning, there is a lack of hope in the idea that human beings can solve the problems of the environment.
At the same time, Darwin's theory of evolution is a view of reality is one in which a more advanced sense of optimism can contrast such a dour view of human generated solutions to the environmental issue. In this logic, human efforts can be driven towards an end in which the elevated undertanding of how humans are responsible for the environment emerges. In this progress towards evolution, there is the idea that once human beings understand their own configuration into the natural order of things in which the problems of the environment is a part, there can be a sense of optimism present.
I would only posit one other item to figure into this configuration. Darwin's view of reality is one in which there is a strong sense of embrace regarding the idea of adaptability. Human beings are creatures, like all others, that understand the need to adapt to situations in order to survive and to find success. Regardless of one subscribes to Darwinian optimism or pessimism, one cannot overlook how a necessary part of this equation is the need to adapt. Darwin concedes that this is a part of what it means to be an organism in the natural setting. In this element of adaptation, there is an intrinsic understanding that the role of the environment is a life sustaining one and its loss ends up becoming catastrophic for all life, inclding human life.