A really - really widely used [1] dataset for validation and climatological studies is the E - OBS [2] dataset. In the current post, mean annual temperature (tg) is mapped for the period 1950 - 2016 over Greece. The 0.25 degrees regular grid was used.

[1] http://onlinelibrary.wiley.com/doi/10.1029/2010JD014123/pdf

[2] http://www.ecad.eu/download/ensembles/download.php

#EOBS