Last month marked the planet's 400th consecutive month with above-average temperatures, federal scientists from the National Oceanic and Atmospheric Administration announced Thursday.
https://www.usatoday.com/story/news/world/2018/05/17/global-warming-april-400th-consecutive-warm-month/618484002/Climate scientists use the 20th-century average as a benchmark for global temperature measurements. That's because it's fixed in time, allowing for consistent "goal posts" when reviewing climate data. It's also a sufficiently long period to include several cycles of climate variability.
"The thing that really matters is that, by whatever metric, we've spent every month for several decades on the warm side of any reasonable baseline," Arndt said.
NOAA's analysis found last month was the 3rd-warmest April on record globally. The unusual heat was most noteworthy in Europe, which had its warmest April on record, and Australia, which had its second-warmest.