Weatherdem's Weblog

Bridging climate science, citizens, and policy

September 2011 (Scripps) CO2 Concentration: 388.95ppm

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The Scripps Institution of Oceanography measured an average of 388.95ppm CO2 concentration at their Mauna Loa, Hawai’i’s Observatory during September 2011.  This reading is from the Scripps’ dataset, not NOAA’s, from which I previously wrote.

That value is the highest value for September in recorded history. Last year’s 386.83 was the previous highest September value ever recorded.  This year’s September reading is 2.12ppm higher than last September’s, which is a significant difference.

The yearly maximum monthly value normally occurs during May. This year was no different: the 394.16 concentration is the highest value reported both this year and all time.

This will likely be the last year that CO2 concentrations will fall below 390ppm during any calendar month. This is the first month during this calendar year which recorded a concentration below 390ppm.  In my last few posts on this topic, I wrote, “Based on the trend from May to September in years past, I expect 2011′s minimum to be ~388ppm.”  We’ll see in early November what October’s average concentration was and how far off my projection was.  I don’t think it will be off by that much.

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