All life requires energy to survive
All life requires energy to survive. We expend the energy in our body to find food which we can consume to produce more energy, and so on. Most animals expend their bodily energy to catch their food directly, but modern humans living in industrial civilization expend their energy to get money to buy food. These are quite different!
Industrial Civilization Humans compared to other animals
Non-humans live nose-to-nose with their ecosystems and live in a 'mutually regenerative' relationship with that ecosystem, meaning that species in stable ecosystems help each other get by even if one species generally eats the other. For example, rabbits will help spread the plants they like to eat. That is, each plant wants its baby plants to spread to new places, and the rabbit does that, and eats some of them in return - everyone wins, and this can be 'sustainable' indefinitely.[0]
"Civilized" humans' primary source of energy is fossil fuels dug up from the ground. We don't eat fossil fuels obviously, but we require them to enable the mining, transportation, manufacturing, war-making, and industrial agriculture that enables our civilization. We can't have a mutually nurturing relationship with these energy sources: they're dead, for one thing, and they're non-renewable so there's no way we can create more. But the energy sources are so rich that we've totally revamped our society over the last ~250 years to depend on them for our food, water, livelihoods, culture, etc. Imagine living without a vehicle, phone, computer, or other technology for a year, and only interacting with businesses that also don't use those: impossible, unless you can live with the land.
We're extremely dependent on these 'dead' (fossil fuel) energy sources, and so society has largely ignored the health of the ecosystems that still live around us. Thus, these ecosystems are rapidly dying off worldwide due to pollution, habitat loss from over-development, and climate change. In fact, we're in a 'mass extinction' - a scale of species loss just as significant as when the dinosaurs died off 65 million years ago.[1] Unfortunately, once the fossil fuels run out or become unaffordable, it'll be hard to return to the way of life of our ancestors - the forests and oceans won't be as rich with life as before.
How should we respond?
I believe the decision is pretty clear: since fossil fuels will be unavailable after they run out[2], and since we'll return to being dependent on healthy ecosystems, we must throw all our efforts to making those ecosystems healthy again before we run out of fossil fuels and before we do further damage. I'll write about my plan to support this in my own life in another essay.
References
[0] Obviously there are parasites and other species not in a mutual relationship with the life they depend on or consume. It's not that every species evolved this 'wisdom'; these are the life relationships we should copy if we want to live sustainably.
[1] http://www.biologicaldiversity.org/programs/biodiversity/elements_of_biodiversity/extinction_crisis/
[2] Note that 'run out of fossil fuels' is an oversimpification - there may fuel in the ground that is uneconomical to retrieve, but either way we won't be able to use fossil fuels to run our civilization after some point.
