From an environmental perspective I have no concern with the world ending, or the human race ending. I don't see either of these things happening. Instead, what I am concerned about is the diminution of the quality of life on earth. That is, a decline in the actual experience of being alive on this planet.
This could be due to less pleasant or healthy conditions or less availability of goods and services (including recreational services provided by natural resources). These things could be caused by pollution of the air, water or sea or by the removal or degradation of natural areas.