It's all a very natural process. As one species expands (humans) other species decline. As one species expands (humans) it over consumes resources and fouls its environment. Eventually the expanding species will exterminate itself, or find a new place it live.  
It is chutzpah to the highest degree to think that we humans are in control of things. Yes, there is a mass extinction coming for humans. The only way to delay it is to hurry the process along. Revert to pre-Industrial Age population levels, to an agrarian society. But that solution is even less popular than reducing our resource use & emissions. 
We have eliminated many of the natural mechanisms for population control (The Four Horseman: Famine, War, Pestilance, and Death) and continue working to eliminate them further. 
So just let nature take its course. Gaia will survive and some new (evolved) species (homo superior?) will be dominant.