Mass extinction date set by science.

[TheBeardedDude]

We aren't extinct, yet

Give North Korea some more time.  

This is one rather obvious example of a causative mechanism by which we may generate our own extinction. And yes, it is something that the average person has no control over. So in trying to prevent our own extinction by numerous different mechanisms, we have to treat them all separately when we can. When they overlap and/or feed into one another, then it becomes more complex.

We can help ensure our survival as a species, if we (not just the US. This isn't a country-specific problem nor an issue that only a singular country needs to worry about) work towards diplomatic solutions to problems (such as nuclear arms) instead of violent ones. Obviously this isn't simple, but it is also clearly possible to prevent nuclear catastrophe even when 2 nations are armed with their fingers on the trigger.

As to the topic at hand of mass extinction driven by human activities that are causing environmental and climatic changes, this means mitigating damage we currently do, while simultaneously trying to undo damage already done. Once again, it isn't easy to do either of these things, but it certainly isn't impossible. It will be nearly impossible though if even the intelligent and informed give up preemptively.