We broke a record this week — but not the good kind. On Thursday, scientists at a research facility on top of the Mauna Loa volcano in Hawaii reported that average daily levels of carbon dioxide in the atmosphere surpassed 400 parts per million for the first time. As the New York Times notes, CO2 levels haven’t been this high for at least 3 million years, meaning that we are likely to see changes to the climate never experienced by humans before. The 400 PPM milestone is symbolic, but it’s a reminder of how global efforts to curb greenhouse gas emissions are failing.

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As early as 1988, NASA scientist James Hansen suggested that 350 PPM represented a tipping point beyond which humanity would have trouble adapting to a rapidly changing climate. “Somehow in the last 50 ppm we melted the Arctic,” environmentalist Bill McKibben told Grist. “We’ll see what happens in the next 50.” As the McKibben quote suggests, it remains to be seen exactly what this will mean for the climate. We know that it will mean more melting ice caps, rising sea levels, and more extreme weather, but because we’re moving into territory that’s beyond the realm of human experience, nobody knows exactly what 400 PPM will look like.

Last summer was the first time scientists saw CO2 concentrations pass 400 PPM, but Thursday was the first time that the average daily level topped the milestone. Now, it appears to be only a matter of time before 400 PPM becomes the new normal. As the New York Times notes, in the Pliocene era — the last time we reached 400 PPM — sea levels might have been as much as 60 or 80 feet higher than they are today. “It takes a long time to melt ice, but we’re doing it,” said atmospheric scientist Ralph Keeling. “It’s scary.”

Even scarier is the fact that CO2 emissions don’t show any sign of slowing — in fact, emissions are accelerating  “Under business as usual, it’s heading to over 600 parts per million. It could go to over 800 parts per million” by the end of this century, scientist Richard Houghton at the Woods Hole Research Center told NPR.

via The New York Times, Grist and NPR