The World’s Carbon Dioxide Levels Just Hit a Staggering New Milestone

John Giles/ZUMA

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The monthly global average concentration of carbon dioxide just broke 400 parts per million for the first time since record-keeping of greenhouse gas levels began.

The milestone, reached last month, was announced by the National Oceanic and Atmospheric Administration on Wednesday.

“It was only a matter of time that we would average 400 parts per million globally,” said NOAA scientist Pieter Tans in a press release. “We first reported 400 ppm when all of our Arctic sites reached that value in the spring of 2012. In 2013 the record at NOAA’s Mauna Loa Observatory first crossed the 400 ppm threshold. Reaching 400 parts per million as a global average is a significant milestone.”

Crossing the 400 ppm threshold is equal parts disheartening and alarming. Less than a decade ago scientists and environmental activists, including Bill McKibben, launched a campaign to convince policy makers that global CO2 concentrations needed to be reduced to 350 ppm in order to avoid massive impacts from global warming. McKibben, who co-founded the group 350.org, explained the significance of that figure in a 2008 Mother Jones article entitled “The Most Important Number on Earth”:

And so we’re now in the land of tipping points. We know that we’ve passed some of them—Arctic sea ice is melting, and so is the permafrost that guards those carbon stores. But the logic of Hansen’s paper was clear. Above 350, we are at constant risk of crossing other, even worse, thresholds, the ones that govern the reliability of monsoons, the availability of water from alpine glaciers, the acidification of the ocean, and, perhaps most spectacularly, the very level of the seas.

[…]

It’s not clear if a vocal world citizenry will be enough to beat inertia and vested interest. If 350 emerges as the clear bar for success or failure, then the odds of the international community taking effective action increase, though the odds are still long. Still, these are the lines it is our turn to speak. To be human in 2008 is to rise in defense of the planet we have known and the civilization it has spawned.

We’re now at 400.

More MotherJones reporting on Climate Desk

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SIX TRUTHS

Reclaiming power from those who abuse it often starts with telling the truth. And in "This Is How Authoritarians Get Defeated," MoJo's Monika Bauerlein unpacks six truths to remember during the homestretch of an election where democracy, truth, and decency are on the line.

Truth #1: The chaos is the point.

Truth #2: Team Reality is bigger than it seems.

Truth #3: Facebook owns this.

Truth #4: When we go to work, we're in the fight.

Truth #5: It's about minority rule.

Truth #6: The only thing that can save us is…us.

Please take a moment to see how all these truths add up, because what happens in the weeks and months ahead will reverberate for at least a generation and we better be prepared.

And if you think journalism like Mother Jones'—that calls it like it is, that will never acquiesce to power, that looks where others don't—can help guide us through this historic, high-stakes moment, and you're able to right now, please help us reach our $350,000 goal by October 31 with a donation today. It's all hands on deck for democracy.

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