The Holocene
I'm going to sound a little alarmist here. My real fear from global climate change is not a warmer planet, but a more highly volatile one.

We live in a very special geologic period. The last ten thousand years are called the Holocene.

Our global climatic record comes from ice cores that extend way back, almost 100,000 years. Looking at the graphs, it appears that the temperature swings during the Holocene have been about 2°C versus 9°C for the rest of the record.

For 100,000 years the average global temperature was far more variable than it has been for the past 10,000. As far as I can tell, there isn't another period in the ice cores like the Holocene. Normal, for our planet, is much wider variability.

Local minimums and maximums can be notoriously unstable, subject to tipping points, where the input of just a little energy pushes the system into a different state. If the Holocene is such a local minimum or maximum (as suggested by the global climatic record), then we can expect a tipping point back into the wider variability of our planet's longer history. You can argue global warming and whether it's caused by humans all you want, but, just as there will be a killer asteroid coming at Earth sometime in the future, there will also be a tipping point out of the mild Holocene.

9°C doesn't sound like much. 2°C is 3.6°F, noticeable but not uncomfortable, 9°C is 16.2°F, about the difference between winter and summer here in Southern California.

Even the mild swings of the Holocene were enough to set off ice ages, droughts and cause the collapse of whole human civilizations.

With the help of technology, we have more control over our environment than any time in the past 10,000 years, but we are talking global temperature change here. Farming depends on a stable climate. Food supplies could be drastically curtailed for years on end. I don't know if greenhouse technology could counter 9°C swings in temperature, but I do know that we would be applying that technology on far larger scales than ever envisioned.

I do believe the human species will survive. We are extraordinarily tough and resourceful, on a par with cockroaches for survivability, but I'm not sure we could maintain our high level of technology.

I'm talking about changes on a geological time scale. I won't see it happen, nor you, no matter how young you are today. But some of our descendants might.