Thing is, if there's not enough food then people will starve and die, Nature doesn't cut us a special deal in that respect. We laughably do our bit for the environment, like those biodegradable bags, that are actually the cause of large swathes of rainforest being cut down in order to grow the material they are made from etc, but the truth is, even things like GM crops etc will not be able to keep pace with our rate of growth.
Our best bet is, always has been, and probably will always remain expansion, that's why I always hold that one of the stupidest things a Government to do is to cut funding to the Space Program because of financial/resource problems, Earth is a closed system, no matter how much we recycle, and we need to open that system up, there are, quite literally, metal mountains and hydrocarbon oceans out there if we can get to them, and the opportunities for Terraforming, particularly places like Mars, could be our only real way out of the problem we are in, at least one that doesn't involve mass starvation, or Logans-Run style Euthenasia.
I don't think mankind is on the brink of destruction or anything, but there's a lot of conceptual deadweight we've dragged with us through the centuries, there's still a distrust of science above and beyond our inherent fear of change, and, more dangerously, there's an apocolyptic tendency to humanity that means you get groups like the '2012'ers or the 'Rapture Ready', who have already convinced themselves we're already into injury time and the whistle is about to blow. It's people like this, who think some kind of third party is going to come along and either fix or destroy everything that leads to us sitting on our hands when we should be taking action.