Only by consensus among scientists 2015 is the hottest. Whether that is the case we do not know, as temperature records have been adjusted, 
adjusted, and adjusted over several decades. For 2015 NOAA presents a wonderful image, presumably more art than science, with a tiny cold hole between Iceland and Canada. The ‘glowing globe with a blue eye’ is based on global average temperature difference to the period of 1951 to 1980. That is gross negligent if not scam. The 1930s ended with almost as high temperatures as during the last decade with the years 1934, 1931, 1938, 1939 in the top league of hottest years since the end of the Little Ice Age about 1850. In late 1939 World 
War II commenced. Four month later the winter in Europe was the coldest for 100 years (more HERE and HERE) and subsequently global temperature broke down for decades, recovering only in the 1980s. What a disaster, if science has one day to admit that it was WWII.
Enjoy the NOAA image as art not more.
NASA/NOAA: Press Release, 20 Jan,2016
Update 06 Feb.:
According World Meteorology Organization: “The global average surface temperature in 2015 broke all previous records….An exceptionally strong El Niño and global warming caused by greenhouse gases joined forces with dramatic effect on the climate system in 2015,” said WMO Secretary-General Petteri Taalas.
In a previous post is assumed that claiming any warming from El Niño is gross nonsense, as the ‘warm water pool’ causing El Niño is too small for any significant global warming impact.
WMO https://www.wmo.int/media/content/2015-hottest-year-record
Previous Post: https://oceansgovernclimate.com/does-el-nino-warm-the-entire-climate-system/
