Polar meltdown Extra dimensions (think this is in the context of particle physics) Discovery of extraterrestrial intelligence Nuclear exchange Creation of life (i.e. synthetic biology) Room temperature superconductors Machine self-awareness Human cloning Pacific earthquake Fusion energy Asteroid collision Deadly pandemic
#5 has already sort of happened, but never mind.
"The twenty-first century is when everything changes..." as the saying goes.
ummm add to that Practical Nanotech (and count the number of days until the human race is destroyed) mind/machine interfacing mind transfer/archival (thats the serious biggie - if you can store a mind you can edit it, or download it somewhere else, or interactively edit your own mind/memories)