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Bridging climate science, citizens, and policy

September 2013 CO2 Concentrations: 393.31ppm


During September 2013, the Scripps Institution of Oceanography measured an average of 393.31 ppm CO2 concentration at their Mauna Loa, Hawai’i Observatory.

This value is important because 393.31 ppm is the largest CO2 concentration value for any September in recorded history.  This year’s September value is 2.17 ppm higher than September 2012′s.  Month-to-month differences typically range between 1 and 2 ppm.  This particular year-to-year jump is just outside of that range.  This year-to-year change is smaller than some other months this year.  For example, February’s year-over-year change was +3.37 ppm and May’s change was +3.02 ppm.  Of course, the unending trend toward higher concentrations with time, no matter the month or specific year-over-year value, as seen in the graphs below, is more significant.

The yearly maximum monthly value normally occurs during May. This year was no different: the 399.89ppm mean concentration in May 2013 was the highest value reported this year and, prior to the last six months, in recorded history (neglecting proxy data).  I expected May of this year to produce another all-time record value and it clearly did that.  May 2013′s value will hold onto first place all-time until February 2014, due to the annual CO2 oscillation that Figure 2 displays.

 photo co2_widget_brundtland_600_graph_201309_zpsa98224c9.gif

Figure 1 – Time series of CO2 concentrations measured at Scripp’s Mauna Loa Observatory in September from 1958 through 2013. added the `350s` to the past few month’s graphics.  I suppose they’re meant to imply concentrations shattered 350 ppm back in the 1980s.  Interestingly, they removed the `400s` from this month’s graph.  So concentrations within 5ppm of a threshold are added to’s graphic.

How do concentration measurements change in calendar years?  Normally, I insert two NOAA graphs here showing 5-year and 50-year raw monthly values and monthly values with the annual trend removed.  Unfortunately, due to the government shutdown, NOAA is not updating their graphics.  As a side note, I also cannot retrieve NOAA and NASA data for my own research.

As a greenhouse gas, CO2 increases the radiative forcing of the Earth, which increases the amount of energy in our climate system as heat.  This excess and increasing heat has to go somewhere or do something within the climate system because the Earth can only emit so much long wave radiation every year.  Additional figures below show where most of the heat has gone recently.

CO2 concentrations are increasing at an increasing rate – not a good trend with respect to minimizing future warming.  Natural systems are not equipped to remove CO2 emissions quickly from the atmosphere.  Indeed, natural systems will take tens of thousands of years to remove the CO2 we emitted in the course of a couple short centuries.  Moreover, human technologies do not yet exist that remove CO2 from any medium (air or water).  They are not likely to exist for some time.  Therefore, the general CO2 concentration rise in Figure 1 will continue for many years, with effects lasting tens of thousands of years.

This month, I will once again present some graphs that provide additional context for CO2 concentration.  Here is a 10,000 year view of CO2 concentrations from ice cores to compare to the recent Mauna Loa observations:


Figure 4 – Historical CO2 concentrations from ice core proxies (blue and green curves) and direct observations made at Mauna Loa, Hawai’i (red curve).

Clearly, concentrations are significantly higher today than they were for thousands of years in the past.  While never completely static, the climate system our species evolved in was relatively stable in this time period.

Alternatively, we could take a really, really long view:


Figure 5 – Historical record of CO2 concentrations from ice core proxy data (red), 2008 observed CO2 concentration value (blue circle), and 2 potential future concentration values resulting from lower (green circle) and higher (yellow circle) emissions scenarios used in the IPCC’s AR4.

Note that this graph includes values from the past 800,000 years, 2008 observed values (10ppm less than this year’s average value will be) as well as the projected concentrations for 2100 derived from a lower emissions and higher emissions scenarios used by the 2007 IPCC Fourth Assessment report.  If our current emissions rate continues unabated, it looks like a tripling of average pre-industrial (prior to 1850) concentrations will be our future reality: 278ppm * 3 = 834ppm.  This graph also clearly demonstrates how anomalous today’s CO2 concentration values are in the context of paleoclimate.  It further shows how significant projected emission pathways could be when we compare them to the past 800,000 years.  It is important to realize that we are currently on the higher emissions pathway (towards 800+ppm; yellow dot).  The last time atmospheric CO2 concentrations were that high, the globe was much warmer, there were no polar ice caps, and ecosystems were radically different from today’s.

The rise in CO2 concentrations will slow down, stop, and reverse when we decide it will.  Doing so depends primarily on the rate at which we emit CO2 into the atmosphere.  We can choose 400 ppm or 450 ppm or almost any other target (realistically, 350 ppm seems out of reach within the next couple hundred years).  Our concentration target value choice is dependent on the type of policies we decide to implement.  It is our current policy to burn fossil fuels because we think doing so is cheap, although current practices are massively inefficient and done without proper market signals.  We will widely deploy clean sources of energy when they are cheap; we control that timing.  We will remove CO2 from the atmosphere if we have cheap and effective technologies and mechanisms to do so, which we also control to some degree.  These future trends depend on today’s innovation and investment in research, development, and deployment.  Today’s carbon markets are not the correct mechanism, as they are aptly demonstrating.  But the bottom line remains: We will limit future warming and climate effects when we choose to do so.


2 thoughts on “September 2013 CO2 Concentrations: 393.31ppm

  1. Pingback: More Discussion on Warming “Hiatus” | Weatherdem's Weblog

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