It's actually very hard to imagine a true extinction level event now. Despite the comments in this thread, it's unlikely to be nuclear (there's just not enough

It's actually very hard to imagine a true extinction level event now. Despite the comments in this thread, it's unlikely to be nuclear (there's just not enough power there - the Earth is really big). If the Earth's population is around 8 billion, even if a series of events killed 99.99% of us - there'd still be 800,000 people left. More than enough to repopulate in time.