The 400 ppm threshold

Last week, for the first time in more than 2 million years, the concentration of carbon dioxide in Earth’s atmosphere reached 400 parts per million.

Two million years.  To put that in perspective, the first animals we now classify in the genus Homo – Homo habilis – showed up about 2 million years ago. But it would be another 1.5 million years until the emergence of our species, Homo sapiens, along with solid evidence for the controlled use of fire by humans.

In the last 200 years, our use of controlled fire has grown both extraordinarily sophisticated and, ironically, out of control. Atmospheric carbon dioxide held basically steady for the previous 10,000 years at about 280 parts per million – until we mastered the controlled burning of fossil fuels and the accumulation of carbon pollution in the air accelerated toward last week’s disturbing milestone.

In a world now supporting billions of Homo sapiens dependent on food production systems that are quite sensitive to climate, consider the crossing of the 400 ppm threshold a global emergency at least as urgent as a massive and deadly pandemic or the most obscene terrorist threat imaginable.

Experts on the climate emergency tell us the “safe operating space for humanity” is in the neighborhood of 350 ppm of atmospheric carbon dioxide.  You are right, astute reader -- we passed that threshold a while ago.

The only way back to Target 350 is to stop putting so much carbon pollution in the air and at the same time to remove a lot of the accumulated carbon from the air. In other words we need to move rapidly from a global economy powered primarily by fossil fuels to a clean energy economy. And at the same time, we’ve got to get busy on biocarbon to restore nature’s capacity to absorb CO2 from the air and store it in living soils, plants, and trees.

Biocarbon, or the second climate solution, is the focus of the Northwest Biocarbon Summit in Seattle on June 10th.  The Summit is a unique opportunity for people engaged in the biocarbon arts—soil-building agriculture, conservation forestry, composting, biochar, natural infrastructure, and restoration of watersheds, wetlands and seagrass beds—to connect, collaborate, learn from each other, and hatch plans.

Together we can build the Northwest into a leading laboratory and incubator of biocarbon solutions that will inform and inspire action around the world.

I look forward to seeing you at the Biocarbon Summit!

Author Bio

Rhys Roth

Director, Center for Sustainable Infrastructure, Climate Solutions

Rhys Roth co-founded Climate Solutions in 1998, and left the organization in July 2013 to create the Center for Sustainable Infrastructure.

To connect with the Center for Sustainable Infrastructure, contact Rhys Roth at or 360-867-6906.

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