[mikeash]

Water is doable as long as you have enough energy to decontaminate it, which is not really a given. Food, I'm not nearly so confident as you. Cows thrive partly because of what we do with them and partly because of all the natural stuff we can use to do so. Sperm whales weren't wiped out because that particular act of environmental destruction was checked before the species disappeared. You can find plenty of examples of species that were hunted to extinction, that just happens to not be one of them.

To say that unchecked destruction of the environment won't necessarily destroy us is the same as saying that we'll be able to create closed-loop life support systems that can operate indefinitely without any outside organic input, and that we'll be able to do it fast enough to save ourselves. I'm highly dubious of that.

[lopmotr]

You're assuming that 'unchecked destruction of the environment" means all important species will be made extinct. That's not true. We do our best to destroy various pests but they keep surviving. Many species have been wiped out and everything's still going fine. How much damage do we have to do to cause important ecosystems to collapse? I'll bet nobody knows because it's too complicated. Again, it might happen but nobody's certain so it's a lie to say that it's certain.

Something I'm pretty sure of though is that we can never destroy all food-producing life on earth by just eating everything till it's gone. Whatever's left will thrive and can be used to make food. Maybe not as tasty or as cheap, but we won't need a fully artificial life support system. Even in an extreme case of desertification, we can still grow plants indoors, and rain will still fall on our "deserts". And that's the very extreme! In reality, maybe the price of beef will go up a little as farmers have to spend more on feeding them.