Carbon dioxide levels in Earth’s atmosphere hit a stunning new milestone over the weekend.

Data from the Mauna Loa Observatory in Hawaii showed that carbon dioxide levels surpassed 415 parts per million on Friday.

“We don’t know a planet like this,” Eric Holthaus, a meteorologist and writer at Grist, wrote on Twitter.

Carbon dioxide (CO2) concentrations have skyrocketed far higher than any levels in the last 800,000 years, data from the Scripps Institution of Oceanography at the University of California – San Diego show, and levels have not been this high for millions of years, Holthaus said.

“This is the first time in human history our planet’s atmosphere has…