There's more to it than climate change.
Yes, the earth's ability to support humans is rapidly decaying, but even if it had remained stable, the future of our species was going to look much different than today, or the recent past.
All animals -- and we are definitely not angels -- follow certain population patterns. Those that grow slowly and steadily tend to decline slowly and steadily. But those that suddenly boom, for whatever reason, almost always bust just as dramatically.
The chart traces human population from 1000 CE to 2200 CE, with population peaking in 2100 at 10 billion. (There are varying estimates of when population will peak, but it will be soon, historically speaking.) Why the sudden drop in 2200? The best predictor of future results are past results, and past results state pretty clearly that rapidly rising populations peak and then drop dramatically.
Now maybe the drop won't be that precipitous. Maybe it will spread out a century or two, but that's how nature works.
Here is where exceptionalists will say "Humans aren't like other species. We control our environment. We are stronger than nature, and we will not suffer the same fate as animals that are so far below us on the evolutionary scale."
And here is where environmentalists will say "Look around."
And where demographers will say "Do the math."
That math is elegantly laid out in a New York Times article, "The World’s Population May Peak in Your Lifetime. What Happens Next?" The story doesn't fuss with climate change or carrying capacity, but rather focuses on a very simple, rudimentary statistic: Birth rates.
Human birth rates are dropping rapidly, so rapidly that if the trends continue, the drop in population shown in the above graph will be borne out, so to speak, in the next century. The infant who comes into a world of growth, a world with an expanding pie that allows some, if not many, to grab a piece without affecting others, will live to see one where the pie shrinks daily, and the battle for crumbs will become more and more intense.
The exceptionalists will point to human ingenuity, and human technology, and say "We'll figure it out."
But you know, humans really aren't that exceptional. We're discovering that our hominid ancestors built shelters and dug graves a hundred thousand years before the emergence of homo sapiens. As our blinders come off, we see more and more intelligence in species that we have disdained, and more and more intelligence in the "instinctual" behavior of animals and insects.
And really, if we are so smart, we should prepare for a future where there are many fewer of us, a future our great-grandchildren will have to navigate. Perhaps we should imagine how a world with 2 billion humans scurrying about the surface might look, and what we could do to prepare posterity for it.
Sadly, we have used up most of the easily acquired resources -- like a 21-year-old given access to a huge trust fund -- and climate change will make the planet less hospitable. Still, even if we have to huddle around the poles, we should try to ensure that what we have learned remains accessible (i.e., tangible, not electronic) and that what can be salvaged is protected.
Of course, the future is an unknown. It could be better, it could be worse. Aliens might arrive to save us -- or eat us. But demography is destiny in many ways, and the most likely road to the future is one completely new to us.
So if we're really that smart, we better start drawing a map.