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The world passes 400 ppm carbon dioxide threshold - 28th September

400 ppm

At a time when atmospheric carbon dioxide is usually at its minimum, September 2016's value failed to drop below 400 parts per million (ppm).

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

Carbon pollution has been increasing since the start of the industrial revolution and has shown no signs of abating, it was more a question of “when” rather than “if” we would cross this threshold.

September is usually the month when carbon dioxide is at its lowest after a summer of plants growing and sucking it up in the northern hemisphere. As Autumn wears on, those plants lose their leaves, which in turn decompose, releasing the stored carbon dioxide back into the atmosphere. At Mauna Loa Observatory, the world’s marquee site for monitoring carbon dioxide, there are signs that the process has begun but levels have remained above 400 ppm.

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,” said Ralph Keeling, the scientist who runs the Scripps Institute for Oceanography’s carbon dioxide monitoring program. “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.”

Read more here.

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