Antarctic ice, sea-level, & rivers
The long-speculated collapse of the west Antarctic ice sheet is underway, and also appears to be on an unstoppable trajectory. According to the recently-published research documenting this (Joughin et al., 2014; McMillan et al., 2014; Rignot et al., 2014) it will likely take a couple of centuries for the ice sheets to transfer their water to the sea (in the case of land ice). Among other things, this means that already rising sea levels will accelerate (see this NASA summary discussion on past meltwater pulses and their effects on sea level: http://www.giss.nasa.gov/research/briefs/gornitz_09/)