Although similar in shape and size, the graphic below is quite different than the typical anomaly or percentile map depicted in these operational State of the Climate reports. The colors on the map below represent time periods. Sepcifically, they represent when the warmest year on record occurred for each of the qualifying grid boxes in the analysis.
Because there are many different individual years, from grid box to grid box, it was necessary to bin the years into their respective decades. For example, a grid box colored darker blue indicates that its warmest year on record occurred during the 2001-10 decade, and so on.
The dominance of blue and light blue on the map indicates that, for the vast majority of the earth’s surface, the warmest year occurred during the 21st century. But this pattern is certainly not universal, as other decades are depicted. There are also rough regional patterns in the maps.
Source: http://www.ncdc.noaa.gov/sotc/global/2015/13/supplemental/page-5
The Decolonial Atlas 