The people my actions are going to affect (both in the present and the future generations) will themselves die eventually. The whole universe will inevitably end with either heat death or a Big Crunch, rendering all personal actions futile. So, in a purely materialistic and cosmological point of view, do the effects of my actions really matter? No, it doesn't.
A Buddhist can look at pictures of decomposing remains and conclude that he must not be worldly. Yet he can also (if he chooses to) look a the same pictures and conclude that nothing hinders him from being worldly, for the worldly and the non-worldly alike will end up rotting in the end; one might as well do as he wishes, for everything is an illusion (ah, that inspired Buddhist phrase!).
For the record, I do not subscribe to the cynical philosophy I tried to illustrate in the above paragraphs. But given that we do not live in a perfect Christian society where such a philosophy would not exist, environmentalists will have to look for better arguments than "it's nice to be nice to other people" and "you can't take your SUV with you when you die". Because in a doomed, absurd, or illusory universe of atheists or Buddhists, "clinging to the first rationalization that allows people to keep doing what they want" is a perfectly rational thing to do.