Life on earth has around 1 billion years left(Sun will be too hot). Without intelligent life all will surely go extinct. We may be its ultimate saviors when/if we conquer the stars.
One perspective is that human population and various other characteristics of the economy & environment roughly agree with the "Limits to Growth" standard run modelling that was done 40 years ago:
I am not sure if "doomed" is the right word. It seems pretty plausible that existing civilisation will collapse, as many human civilisations have done in the past, and there will be additional human suffering (more than the considerable amount there is now), but I doubt we as a species will become extinct within the next few hundred years.
Comparing the odds that we will destroy it with global warming or nukes is tough though. Seems like we may well be the arbiter of it's doom.
Plus, what if we do leave? Do you think our governments are really progressing towards that Star Trek enlightened super government, or are we progressing toward some sort of Orwellian nightmare? What would humanity look like when it colonizes more planets and leaves? Would we be the good aliens or bad aliens you see in sci-fi movies?
Right now we still seem like a species dominated by self interest, and it doesn't look like we're changing any time soon...
Meh, climate change might make it more or less comfortable for us and other creatures, but it won't "destroy" anything, and I seriously question whether human beings, marshaling every last bit of technology we have at our disposal right now, even have the power to "destroy" the earth. I'm almost certain we do not.
One thing we do have, though, is the power to amplify our own significance. We've only been writing about what happens to us for 5000 years or so. There are Bristlecone pine trees nearly that old, and even that is just the tiniest little flash, so brief it is undetectable, in the time that the planet has been here.
Bingo. We need to keep the biosphere stable/habitable and preserve a good amount of biodiversity, but ultimately all species and all of their decendant species will go extinct in a short period of time (on a universal scale).
We have the duty to prevent that if possible. Using near future technology we should be able to at least ensure some life survives the death of our star. Easily imagined technology would let us spread life far enough to survive almost any catastrophe. It will be up to some future life forms to figure out how to escape the heat death of the universe... We can only do so much after all.
Hah, that sure is an interesting way of looking at it! Just as aerobic organisms saved life on Earth from the Great Oxygenation Event, and fungus & bacteria saved life on Earth by recycling, humans could save life on Earth from the Sun by developing space travel.
We are, you could say, one of Nature's many apparatus to long term success. Any biosphere that does not develop space travel is doomed to eventual extinction.
I have believed for a long time that the moral imperative of humanity as a species is to propagate the Earth ecosystem to other planets and in artificial space habitats.
Except for the dolphins. We don't need to encourage other species to just dick around all day. That's our niche.
http://cl.ly/image/3H1A3S341k1t
Of course, we might muck it up good in a few short years here.
Edit: who on Earth decided this was a good comment to downvote? We are doomed.