Photo: AP

It’s a foregone conclusion that as long as the world keeps emitting carbon dioxide, we’ll keep setting records for how much ends up in the atmosphere. But that doesn’t make the recent high water mark of carbon dioxide any easier to swallow.

On Saturday, scientists recorded the first ever carbon dioxide reading above 415 parts per million (ppm) at the Mauna Loa Observatory. They’ve been measuring carbon dioxide levels continuously since 1958 at that location, but ice cores and other data show that it’s not just the highest carbon dioxide has been in 61 years of data. It’s the highest its ever been 800,000 years of data, and that should give us pause about the unsettling planetary experiment we’ve initiated.


Plot atmospheric carbon dioxide measurements and you’ll see they follows a sawtooth pattern over the course of a year. Carbon dioxide dips from summer into early fall as northern hemisphere plants suck it out of the atmosphere, and rises from late fall into spring as plants decompose and release carbon dioxide back into the atmosphere. This was all going on largely unchanged from year-to-year until humans started using the atmosphere as a dump for carbon dioxide.

Now, the sawtooth pattern has been set on edge, rising year over year and setting new records each spring. The resulting graph—one of the most iconic data visualizations in science—is known as the Keeling Curve. In February, the world passed the record set last year. And on May 11, carbon dioxide cracked 415 ppm for the first time in human history.

Natural fluctuations like El Niño—marked by a warming of the waters in the eastern tropical Pacific—can speed up the rise but human activities are what have driven carbon dioxide to its new milestone. Sure, it’s just a number. The climate is only slightly more screwed at 415 ppm than it was at 414 ppm. And next year, we’ll rocket past 415 ppm.


But it’s worth taking stock of what it took to get us here and the choices in front of us. The world has known for decades carbon emissions have put it on a path toward dangerous climate change. The greenhouse effect was established long before that. And yet rather than tap the brakes, carbon emissions have sped up. At the start of the Mauna Loa Observatory record, it took 16 years for atmospheric carbon dioxide to rise 15 ppm. It took 6 years to do the same from 2010-2016. It feels like only a few years ago we were worried about crossing the 400 ppm threshold, which wait. We were.

The great carbon acceleration has created an atmosphere unlike one any human has ever seen. And it means the climate is turning into one we’ve never known either, one with super charged heat waves, violent rising seas, and ecosystem failure. But that’s not even the scary part.


These are the changes we’re seeing now with about 1 degree Celsius (1.8 degrees Fahrenheit) of warming. Because carbon dioxide sits in the atmosphere for centuries, the climate will warp even further. And with emissions hitting a new peak in 2018, the world isn’t backing away from the brink anytime soon. Instead, we’re racing toward it.

None of which is to say we need to keep running toward catastrophe. The world’s leading scientists have laid out a series of choices we can make to avert it. It’s up to the world and world leaders in particular to look at that map and chart which roads they want to travel.