The monthly anomaly of the global average surface temperature in May 2015 (i.e. the average of the near-surface air temperature over land and the SST) was +0.38°C above the 1981-2010 average (+0.75°C above the 20th century average), and was the warmest since 1891. On a longer time scale, global average surface temperatures have risen at a rate of about 0.70°C per century.
1st. 2015 (+0.38°C), 2nd. 2014 (+0.31°C), 3rd. 1998 (+0.27°C), 4th. 2010 (+0.23°C), 5th. 2012 (+0.22°C)