I usually hate anything and everything with an environmental theme (way too preachy), but I thoroughly enjoyed this. It reminded me of Isaac Asimov's "The Last Question", the plot and tone were along the same vein. The art was attractive, especially the couple of full-color pages in the beginning. It's pretty short (one-shot), so there isn't much more I can say, but I recommend it!
(Didn't get full marks because the brief chibi-humor felt weird, and I wasn't quite pleased with the ending, but everything else was great)