“The rate of CO 2 growth over the last decade is 100 to 200 times faster than what the Earth experienced during the transition from the last ice age. This is a real shock to the atmosphere.” — Pieter Tans, lead scientist at NOAA’s Global Greenhouse Gas Reference Network

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It wasn’t too long ago that we were talking about atmospheric CO2 crossing the key 400 parts per million threshold. That was 2014. But now, just three years later, atmospheric levels of this key heat-trapping gas are climbing to within striking distance of another, and still more dangerous, atmospheric milestone. 410 ppm.

That’s an increase in the peak atmospheric CO2 value of around 3 ppm per year or more. One that gibes with record annual rates of atmospheric accumulation of this heat trapping gas during 2015 and 2016. And as we approach a new high water mark for atmospheric carbon, we’ve left the 400 ppm level so far behind that it’s likely that we’ll never see even a single day where values at the Mauna Loa Observatory fall below that threshold.

Approaching Another Milestone for Key Heat-Trapping Gas

Instead, primarily through our rampant and incessant burning of fossil fuels, we are racing head-long into an ever-more uncertain climate future:

(The world hasn’t seen such high levels of atmospheric carbon in millions of years. And all that extra carbon is sucking a considerable amount of Earth-altering heat into its atmosphere and oceans. Image source: The Keeling Curve.)

Since late February, weekly and daily CO2 values have ranged between 405 and 409 parts per million. But as CO2 typically peaks during April and May before Northern Hemisphere vegetation begins to draw down carbon in the months of June through September, it appears that we are likely to see top monthly atmospheric CO2 values hit between 409 and 410 parts per million during 2017.

Out of Context Problem

Back in 2014, we were talking about how atmospheric CO2 levels hadn’t been so high in about 3 million years. But a near 410 ppm high water mark would push those comparative timeframes back to between 5 and 15 million years when the world was about 3-4 degrees Celsius hotter than today and atmospheric CO2 ranged from 400 to 500 parts per million (to this point it’s worth noting that atmospheric CO2 equivalent gasses like methane, when added to presently high CO2 levels, will produce a combined total forcing equal to around 493 ppm CO2e by end 2017).

Back then, ocean levels were meters to tens of meters higher than today, the glacial ice of Greenland and West Antarctica was gone or greatly reduced, and even East Antarctic Ice Sheets were smaller. It’s also worth noting that back then, the great apes had just begun to appear and that the first fully developed ancestors of modern humans were still far off.

(NASA provides a new 3-D visualization of carbon dioxide accumulating in the Earth’s atmosphere. Video source: NASA and The Hindustan Times.)

Human beings, and even our furthest distant ancestors, have not experienced climates of the kind we are locking in now.

But as increasingly tough as our present climate situation may seem, there’s another wrinkle to the tale. For from 5-15 million years ago to now, billions of tons of carbon in the form of plant and animal remains has been sequestered in the world’s forests, peatlands, permafrost and oceans. And as the heat-trapping gasses that we have now placed into the atmosphere, primarily through fossil fuel burning, stresses those stores, we risk creating a further warming response coming from the Earth System. Such high atmospheric thresholds should, therefore, be viewed as in a range that produces considerable risk of crossing key climate tipping points and of locking in harmful Earth System changes for very long time periods. And we continue to add to that risk by burning more fossil fuels.

Links:

The Keeling Curve

NOAA ESRL

Following Carbon Dioxide Through the Atmosphere

Human Evolution

Climate Epochs: Miocene

Atmospheric Carbon Dioxide Hits Record Levels