I'm confused by the 'likely to create an event in the next 30 years' part - either it's unlikely or it's likely. There are events that are quite likely, but with a low _perception_ of risk. Oil spills happen all the time, it's just been a while since one has happened in a rich Western country. Why? Because we've already tapped almost all of our oil - most of the worst spills happened long before we were born! Now the spills happen in places like the Middle East and Nigeria, but because only poor people live there, nobody notices or cares.

Other events that were or will be likely to occur, but have a low perception of risk, include the recent financial crisis, and, looking forward a decade or two, ocean level rise flooding major cities, and a US debt default.

Some interesting events that (seem to) have a genuinely low probability, but would really change the world if they happened:

* Asteroid hit (either a big one, or a smaller one that hits just right).

* A 'supervolcano' eruption that puts us into nuclear winter

* Solar flares fry every piece of electronics on the planet

* Sudden tipping point in the Antarctic or Greenland ice sheets that raises ocean levels by a few meters over a year.

* A strong 'godlike' AI (benevolent or otherwise)

* A self-replicating nanoassembler

* Godzilla attack