Most def. Personally, I'm less afraid of us obliterating the earth than of the fact that the earth has a balance it enforces and how swiftly and easily it wipe us out as our manipulations of the environment continue to upset the balance.
Boring science warning: I'm going to quote another scientist (sorry can't help myself) when I say terrorism is unfortunately less horrifying than the fact that we are currently losing the battle against microbes and bacteria. Joshua Lederberg claims bioweapons are by far more of a tangible threat than other WMDs, yet the government won't research counter-measures. He's certainly not very optimistic--"The future of humanity and microbes likely will unfold as episodes of a suspense thriller that could be titled 'Our Wits Versus Their Genes." I hope he's wrong about one thing in his life.
Our maladaptively complex brains, complex psychological makeup (which makes us tend to be neurotic enough to use anti-bacterial soap, kill all but the strongest bacteria, create superstrains, then touch the bathroom door on the way out) and its brainchild, capitalism, might be the end of us.
Cockroaches might not even survive if they keep relying on our waste for food.