Planet Earth has just passed a major climate milestone, and we have “the monster El Nino of 2015-2016” to thank for it, Gizmodo reports.

While El Nino is reportedly over now, “scientists are still coming to terms with its impacts on the planet,” the story reports. “Among those impacts: charging up the global carbon cycle and pushing atmospheric CO2 levels above 400 parts per million (ppm) for an entire year — a first in human history.”

Baseline carbon levels, which are monitored at the Mauna Loa Climate Observatory, have been climbing by about 2.1 ppm annually, fueled in large part by fossil carbons emitted by cars and factories, the report notes.

“This past year was special,” the story adds. “As Gizmodo reported in March, carbon concentrations at Mauna Loa rose 3.76 ppm between February 2015 and February 2016; the single largest jump in recorded history. The previous record rise, of 2.82 ppm, occurred during the 1997-1998 El Nino. In both cases, scientists believe that emissions spiked due to a combination of warming and drying in the tropics, which can accelerate soil carbon decomposition, and large, drought-fueled fires.”