Weatherdem's Weblog

Bridging climate science, citizens, and policy

May 2012 CO2 Concentrations: 396.78ppm

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The Scripps Institution of Oceanography measured an average of 396.78ppm CO2 concentration at their Mauna Loa, Hawai’i’s Observatory during May 2012.

396.78ppm is the highest value for May concentrations in recorded history. Last year’s 394.16ppm was the previous highest value ever recorded.  This May’s reading is 2.62ppm higher than last year’s.  This increase is very significant.  Of course, more significant is the unending trend toward higher concentrations with time, no matter the month or specific year-over-year value.

The yearly maximum monthly value normally occurs during May. Last year was no different: the 394.34 concentration was the highest value reported last year and, prior to the past two months, all time.  This May’s value is, as usual, the highest recorded this year – and thus all-time in modern history.  If we extrapolate last year’s value out in time, it will only be 2 years until Scripps reports 400ppm average concentration for a singular month (likely May 2014).  Note that I wrote in past posts that this wouldn’t occur until 2015.

It is worth noting here that stations measured 400ppm CO2 concentration for the first time in the Arctic earlier this year.  The Mauna Loa observations represent more well-mixed conditions while sites in the Arctic and elsewhere more accurately measure local and regional concentrations.

Judging by the year-over-year increases seen per month in the past 10 years, I predict 2012 will not see an average monthly concentration below 390ppm.  Last year, I predicted that 2011′s minimum would be ~388ppm.  I overestimated the minimum somewhat since both September’s and October’s measured concentrations were just under 389ppm.  So far into 2012, my prediction is holding up.

CO2Now has the following graph on their front page:

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It shows concentrations for the month of May in the Scripps dataset going back to 1958. As I wrote above, concentrations are persistently and inexorably moving upward. Alternatively, we could take a much longer view of CO2 concentrations:

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Given our historical emissions to date and the likelihood that they will continue to grow at an increasing rate in the next 25 years, we will pass a number of “safe” thresholds – for all intents and purposes permanently as far as concerns our species. It is time to start seriously investigating and discussing what kind of world will exist after CO2 concentrations peak at 850 and 1100ppm. I don’t believe the IPCC or any other knowledgeable body has done this to date. To remain relevant, I think the IPCC will have to do so moving forward.

As the second graph implies, efforts to pin any future concentration goal to a number like 350ppm or even 450ppm will be insanely difficult: 350ppm more so than 450ppm, obviously. Beyond an education tool, I don’t see the utility in using 350ppm – we simply will not achieve it, or anything close to it, given our history and likelihood that economic growth goals will trump any effort to address CO2 concentrations.

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