If you expect some sort of dramatic event, with the sky darkening and demons rushing out to the sound of trumpets, it's not going to be like that.
What's going to happen, is that the world is going to get shittier a little bit every year. A few more days of unbearable hot in the summer. A storm a little bit more violent than the previous one. Crops failing a little more than the previous year, etc. Nothing dramatic, nothing radically changing in an instant, nothing you would say "oh, that's not normal" because it'll be small enough that you'll think it's just bad luck. Little by little, slowly turning this place into hell. And over the course of a hundred years, it'll be exactly hell.
The actions that we should take are not really to prevent a dramatic change from paradise into hell over the course of 6 months. It's to prevent the total amount of shittiness that's going to happen in the coming century, with the speed of change remaining more or less constant. We do nothing? The total amount of shit in 100 years is going to be enormous. We do something before that 3 years deadline? The total amount of shit in 100 years is reasonable.
So yeah, if you're over 50, you basically don't give a shit. Nothing is going to happen quick enough to bother you. And even if it does, you already had 50 years of cool stuff. I can get you're on the "so long, suckers!" mentality.
It's like taking a credit in the name of someone else. You get the stuff, and someone else has to pay back. There's got to be careless people with a system like that... Well, that's exactly what happened with climate and the environment. One generation getting the stuff and letting the following ones paying back.