They are not measuring the temperature of the worlds oceans. Only the shallow surface waters. Therefore they have no clue that the volume of deep cold ocean water has been increasing. And that is all that matters.
The Argo buoys measure the deeper water temps. down to 2000 m.
Interesting actual data here -
http://wattsupwiththat.com/2014/03/02/argo-temperature-and-ohc/