One of the watchwords here at Rabett Run has been RTFR, a derivative of RTFM but no less trenchant advice. So with everybunny jumping up and down about the baselines and adjusting boats to buoys or whatever (Zeke has a nice summary at ATTP), Eli though he would take his own advice, and thanks to the kindness of Climate Peter, he found the article which introduced ERSSTv.4
On page 928 in the summary Eli finds
Buoy SSTs have been adjusted toward ship SSTs in ERSST.v4 to correct for a systematic difference of 0.12 C between ship and buoy observations. Although buoy SSTs are more homogeneous and reliable than ship observations, buoys were not widely available before around 1980. However, the selection will not affect the evolution of the SSTAs. Further studies are needed to consider the potential of including C-MAN SSTs and other near-surface ocean temperature measurements not presently incorporated in ERSST.v4 (e.g., from oceanographic profiling instruments).Pleasingly pretty much saying what Rabett Run has been telling one and all. Ocenographic profiling instruments Eli assumes includes the Argo float network which only went operational about five or six years before the HRSSTv4 data set was done.
Oh yes, the timeline first submitted 20 December 2013, accepted 3 October 2014 and appeared on line 4 February 2015, so as they say, out there well before the Karl et al paper appeared in June. ERSST.v4.