Global atmospheric CO2 concentration, 2011-2016. The lower value of CO2 concentration passed 400 ppm in September 2016, and won't fall below 400 ppm 'ever again for the indefinite future.' Graphic: Climate Central / Scripps Institute of Oceanography / Mauna Loa Observatory

27 September 2016
By Brian Kahn

(Climate Central) – In the centuries to come, history books will likely look back on September 2016 as a major milestone for the world’s climate. At a time when atmospheric carbon dioxide is usually at its minimum, the monthly value failed to drop below 400 parts per million.

That all but ensures that 2016 will be the year that carbon dioxide officially passed the symbolic 400 ppm mark, never to return below it in our lifetimes, according to scientists.

Since the industrial revolution, humans have been altering this process by adding more carbon dioxide to the atmosphere than plants can take up. That’s driven carbon dioxide levels higher and with it, global temperatures, along with a host of other climate change impacts.

“Is it possible that October 2016 will yield a lower monthly value than September and dip below 400 ppm? Almost impossible,” Ralph Keeling, the scientist who runs the Scripps Institute for Oceanography’s carbon dioxide monitoring program, wrote in a blog post. “Brief excursions toward lower values are still possible, but it already seems safe to conclude that we won’t be seeing a monthly value below 400 ppm this year – or ever again for the indefinite future.” [more]

The World Passes 400 PPM Threshold. Permanently



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