I believe the technological singularity is the most imminent existential threat humanity faces at this very moment. Whether the advancement and intersection of biotech, nano-tech, and artificial intelligence algorithms will yield the apocalypse or utopia is still up in the air. Either way it will fundamentally change our existence within the century. Thus I give you an introduction to the academic debate surrounding these issues according to Murray Shanahan (cognitive roboticist). If you are still not convinced you should read this consider the following:
Imagine trying to explain evolution to an ant. Impossible. We humans have an intelligence that surpasses that of an ant and thus we spend little time worrying about the many ants we may have killed over the years doing what we do. We are now on the cusp being capable of producing a super-intelligence. Imagine what discoveries this intelligence will make. Imagine this intelligence trying to explain those discoveries to us. Impossible. These super-intelligent entities have an intelligence that surpasses our own and thus may spend little time worry about the many humans it may kill over the years doing what it does.
That is a rather apocalyptic scenario, but scary things tend to make people act. I hope you take action and read this book.