The challenge of the 20th century was that humanity could go extinct if a few well-positioned people happened to be reckless, extreme, paranoid, or (in the right cases) deceived.
We managed to meet that challenge (so far).
The challenge of the 21st century is that humanity could go extinct if all of us just keep on living our lives in our normal pattern.
That's a far more difficult challenge to tackle.
We are, as you don't need me to tell you, rapidly racing towards ecological catastrophe. Global warming is approaching runaway levels, threatening a chain-reaction of climatological forces which may well be irreversible and would make human life on Earth impossible. Estimates differ, but the breakout point is almost certainly within this century.
But ironically, along a similar timeframe, we're also racing towards the technological developments that could save us. These are (a) limitless renewable energy and (b) genuine artificial intelligence. If those two currencies -- energy and intelligence -- start to get on a runaway train, then all of the sudden we're back in business. Infinite energy + infinite computing power = ability to solve essentially any problem (certainly in particular the problem of freezing, or potentially even reversing, greenhouse gas emissions). And the breakout points for each of these are, I'd wager, also within this century. So short-term strategies with respect to climate change might simply be delaying actions (see: how nukes might save the world). What we need to do is buy the computers enough time to save us all.
But basically a race. Can we get to free energy and free computation before we get past a climatological point of no return? What's amazing to me is that I genuinely, truly believe it's a toss-up -- and that we'll probably find out the answer (one way or another) in my lifetime.
Of course, the advent of true AI might bring about a whole new host of existential/extinction-level problems (one of the most interesting aspects of the lore of Horizon: Zero Dawn is that they make it quite clear humanity managed to avoid the ecological apocalypse ... only to stumble into a self-replicating killer robot apocalypse). But one disaster at a time.