Spoiler Alert - The Earth's poles flip!!! Doesn't anyone remember the spinning compass scene? This phenomenon is fairly common throughout the Earth's history and would cause the oceans to become slightly erratic (possible tsunamis), the surface of the planet would become weak in spots causing earthquakes and volcanos (the ash), weather would get weird, satellites would become lost or destroyed (knocking out communications), power grids would get tweeked, etc.
Overall, I thought this was a pretty good movie. It had some very tense and suspenseful moments. It is always interesting to dive into the psychology of what people would do when all the creature-comforts we take for granted are gone and survival instincts take over.
I give it a 7/10 because the ending was abrupt and left you wanting some closure.