The human species experienced an alarming milestone this weekend: for the first time since Homo sapiens evolved, atmospheric carbon dioxide levels surpassed 415 parts per million (ppm), CNN reported.
The carbon dioxide high was recorded by the Mauna Loa Observatory in Hawaii and tweeted out by the Scripps Institution of Oceanography Saturday, which regularly updates C02 levels. The observatory recorded a daily C02 reading of 415.26 ppm, which is the first time the daily level topped 415 ppm.
Meteorologist and climate action advocate Eric Holthaus sounded the alarm about that data point in widely-shared retweet.
"We don't know a planet like this," he said.
Carbon dioxide levels did not top 300 ppm in the 800,000 years before the industrial revolution, according to USA Today. A study in April used computer models to confirm that carbon dioxide levels today are the highest they have been in three million years. The study also showed that current levels would be at around 280 ppm if it weren't for the burning of fossil fuels by human beings, leading to climate change.
The last time carbon dioxide levels were this high was 5.3 to 2.6 million years ago during the Pliocene epoch, when beech trees grew in Antarctica, temperatures were three to four degrees Celsius warmer and sea levels were 20 meters (approximately 65.6 feet) higher.