The best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

• The ocean covers 71% of the globe and drives average temperatures;
• SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
• A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through February 2018.
Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily…