As of May 31st the 2016 trend line is lowest on the graph. A sea ice volume decrease of 3037 km3 during the month of May was enough to overtake 2011 and increase the lead over every other year in the 2007-2016 period, except for 2010 and 2012, which both recorded massive volume losses during May. 2016 has a very small lead now over 2011 (162 km3) and 2012 (270 km3). The gap with last year has grown to a whopping 2180 km3.
Here's how the differences with previous years have changed since last month:
Wipneus' version of the PIOMAS volume graph also shows how close the 2011, 2012 and 2016 trend lines are: