Climate outlooks are probabilistic meaning they give a percent chance (%) for a certain outcome.  They do not guarantee (100%) any particular outcome in all locations.  As illustrated by the rainfall in California over the last month or so, the 33-40% chance of below-median precipitation in southern CA is not panning out.  This does not mean these predictions are worthless.  As Rebecca has pointed out in the previous comment the goal is to be correct more often than random chance.  To properly evaluate probabilistic outlooks one has to look at many years of forecasts to see if they are reliable.  Meaning that, over a long time period, when we say there is a 40% chance of something happening in a particular location, it should actually occur roughly 40% of the time (meaning that 60% of the time this outcome should *not* occur).  

The IPCC projections also provides probabilities or a range of the *most likely* outcomes depending on future emission scenarios.  You can read the AR5 summary clicking here.