When will next halving events occur? I've read in some places that the next halving event will be on 2016. How can this be estimated?
The Bitcoin reward schedule follows a predetermined pattern, see Controlled supply from the Bitcoin wiki.

The next reward drop will happen at block number 420000. The current block number at the time of writing this answer is 318662. There are about 101338 blocks remaining. At approximately 10 minutes per block, there are approximately 1008 blocks per week, and 101338 divided by 1008 is about 100.5. So you can expect the next reward drop approximately 100 weeks from now, or around August 2016.

The http://bitcoinclock.com site does this calculation for you and provides an estimate right at the top. At the time of writing this answer, it says:


  Reward-Drop ETA: 2016-08-05 12:47:44 UTC (100 weeks, 3 days, 17 hours, 40 minutes)