Just over a year ago, atmospheric carbon dioxide (CO2) levels hit 410 parts per million (ppm) for the first time in millions of years. And we just hit another worrying threshold in April: levels averaged higher than 410 ppm throughout the whole month for the first time. Geochemist Ralph Keeling said, “We keep burning fossil fuels. Carbon dioxide keeps building up in the air. It’s essentially as simple as that.”

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The Keeling Curve, a daily record of atmospheric CO2 levels made at the Mauna Loa Observatory, started in 1958. Back then measurements were around 315 ppm. 60 years later, we’ve passed the 410 ppm threshold, and in April, the average concentration was 410.31 ppm. According to the Scripps Institution of Oceanography, “This marks the first time in the history of the Mauna Loa record that a monthly average has exceeded 410 ppm.”

Related: CO2 levels just reached 410 ppm — the highest in millions of years

The Washington Post pointed out CO2 levels have hit 400 ppm in the past — such as over three million years ago in the mid-Pliocene warm period. But the Pliocene level “was sustained over long periods of time, whereas today the global CO2 concentration is increasing rapidly,” according to scientists in the Fourth National Climate Assessment, Volume 1, a 2017 federal report.

Smokestacks glimpsed above the clouds in Kentucky

Before the beginning of the Industrial Revolution, CO2 levels fluctuated over thousands of years, but according to the institution, never exceeded 300 ppm once in the past 800,000 years. Around 1880, CO2 levels were about 280 ppm. Today, they’re around 46 percent higher.

Climate scientist Katharine Hayhoe said about the milestone on Twitter, “It’s as if we discovered that something we eat every day is causing our body to run a fever and develop all kinds of harmful symptoms — and instead of cutting back, we right keep on eating it, more and more. If that isn’t alarming, I don’t know what is.”

+ Scripps Institution of Oceanography

Via The Washington Post

Images via Devin McGloin on Unsplash and Nik Shuliahin on Unsplash