May 2018 global temperature, at 0.82°C relative to the 1951-1980 base period, was the fourth warmest May since reliable measurements began in 1880. The warmer Mays were in 2016 (+0.91°C), 2017 (+0.88°C) and 2014 (+0.85°C). Northern Hemisphere spring (March-April-May) 2018 was the third warmest spring at 0.86°C (See the figure above), while the warmest were 2016 (1.10°C) and 2017 (0.97°C). Note that the most of the U.S. was extremely cold in April and very warm in May.
Using the base period 1880-1920 which provides our best estimate of pre-industrial temperature, the May 2018 anomaly was 1.09°C. Post-El Nino cooling has probably bottomed out, given that equatorial Pacific Ocean temperatures have begun to rise (See the left side of the figure below). We conclude that global warming, with short-term variability excluded, has reached the level of at least +1.1°C relative to pre-industrial temperature.