We humans are the greatest threats to the world. Having said that I think that climate is currently our biggest issue. In Denmark we've experienced record temperatures and had the warmest month of may in 139 years (as long as we could record temperature).

Something is really wrong and it's terrifying to think that storms, hurricanes and such are getting amplified due to the planet heating. Unfortunately I will take a lot to change and due to powerfull lobbyism it probably won't happen soon.
Go Thorium Reactors!