According to the National Aeronautics and Space Administration (NASA), Earth's average global surface temperature in 2019 was the “...second warmest since modern record-keeping began in 1880” and this continues the planet's long-term warming trend, with the last five years being the warmest of the past 140 years. The hottest year on record is 2016.
Will 2021 be the hottest year on record according to NASA?
This will resolve on the basis of an announcement by NASA on whether 2021 is the hottest year on record — more specifically, whether Earth’s average global surface temperature in 2021 will be the hottest in the 1880-2021 time frame.
If the NASA (GISS) results are tied with another year, the NOAA numbers will be used to break the tie. If those are tied too, we'll go on to EU's Copernicus. If a tie remains, this resolves ambiguous.