One of the core tenets of the philospophy of geography is Determinism versus Probabilism and I see that being debated out here. What this basically translates to is Does the Earth control the actions of Man, or does Man control the actions of the Earth. There are, of course, viewpoints on either side - from the Probabilist angle, look how Man has shaped the environment in terms of the landscape for his needs and wants. My first two degrees were in Physical Geography and Glaciology and I come as a determinist - in that ultimately the Earth does control Man as through volcanoes, earthquakes, hurricanes and all the rest, the Earth can seize back 'control' and push Man back.
Now I am not a doom and gloom Armegeddon merchant. Yes, there are potential major catastrophes out there but let's be at least rational here. The worlds biggest supervolcano crater caldera is indeed 2/3rds full - however, it will take another 250k years for that to fill and go bingo. Secondly, an ice age is not going to occur in our or our children's lifetime. Thirdly, there is no evidence of global catastrophic plate tectonics destroying the globe - yes, major events and tsunamis on a regional basis )like the 1755 Lisbon earthquake which had some impact on us. Fourthly, switching of the magnetic poles - no evidence here in the past that it has affected flora, fauna and our early neanderthal ancestors (could be interesting for communications though). Fifthly, meteorites/asteroids - we would have a pretty good idea of something impending a few years out.........
I could go on. Perhaps the biggest risk is indeed Man himself - through a nuclear war......The Japanese nucear plant is not yet a Cherbonyl and not likely to be as it does appear the main reactors are holding, Yes it would be a major tragedy if it did advance another stage (but the Japanese are hoping to have electricity back into their cooling systems tomorrow), but it would not close down the world and kill us all