I voted "never" because I am realistic. I see a lot of people "worrying" about hypothetical extinction level events. You cannot live in fear of "what if" situations or worry about things that you, as an individual have no control over.
I wasted far too much time living in fear. Here is what you need to concern yourself with. Am I a good friend? Am I a good neighbour? Am a good child toward my parents? Am I a good sibling? Am I a good colleague? Am I a good spouse? Am I a good significant other?
How you live and how you treat others in your life is what matters most over everything including how much money you have or your other accomplishments.
I realized that I had wasted so much of my life accumulating wealth and things instead of friendships and relationship. I also wasted time worrying about things too much both inside and outside of my life and not enough on building relationships to be stronger and more meaningful.
If you are still young, stop with this worrying bullshit and get out there and live life to the fullest. Stop giving a shit about this science crap if you are not a scientist. It is a waste of time to spend your time on an obsession like that. Get out and socialize because you only have one life and it is short.