It is due to the adjustments of the ocean temperature data. The SST data has been adjusted upward. Due to the adjustments the global temperature is estimated

It is due to the adjustments of the ocean temperature data. The SST data has been adjusted upward. Due to the adjustments the global temperature is estimated to be warmer in the past than the raw data show (http://variable-variability.blogspot.com.au/2015/02/homogenization-adjustments-reduce-global-warming.html http://variable-variability.blogspot.com.au/2015/02/homogeni...)