December of 1984 was the last time Earth had a cooler-than-average month, according to climate scientists, which means April marked the 400th consecutive month the planet saw above-average temperatures.
"We live in and share a world that is unequivocally, appreciably and consequentially warmer than just a few decades ago, and our world continues to warm," said NOAA climate scientist Deke Arndt. "Speeding by a '400' sign only underscores that, but it does not prove anything new."
"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.
The reasonable baseline used by climate scientists is the 20th Century average, due to the fact that it allows for consistent “goal posts” when reviewing data and is a long enough time frame to include several cycles of climate variability, reports USA TODAY.
Europe saw its warmest April on record, Australia had its second-warmest, and Argentina experienced its warmest April since its record-keeping began in 1961.
The United States did not get in on the action, however, with an average temperature of 48.9 degrees -- 2.2 degrees below average and constituting the "13th-coldest April on record and the coldest since 1997", according to NOAA.
Another milestone was reached in April, also related to the number "400": Carbon dioxide — the gas scientists say is most responsible for global warming — reached its highest level in recorded history at 410 parts per million.
This amount is highest in at least the past 800,000 years, according to the Scripps Institute of Oceanography.