Weatherdem's Weblog

Bridging climate science, citizens, and policy

December 2013 CO2 Concentrations: 396.81ppm

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During December 2013, the Scripps Institution of Oceanography measured an average of 395.10 ppm CO2 concentration at their Mauna Loa, Hawai’i Observatory.

This value is important because 395.10 ppm is the largest CO2 concentration value for any December in recorded history.  This year’s December value is approximately 2 ppm higher than December 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, but is smaller than some other recent months.  For example, February 2012’s year-over-year change was +3.37 ppm and May 2012’s change was +3.02 ppm.  Of course, the unending long-term 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. 2013 was no different: the 399.89ppm mean concentration in May 2013 was the highest value reported last year (neglecting proxy data).  May 2013’s record will hold until the end of February 2014 when the annual cycle pushes a monthly value above the record.  Just like in years past however, May 2014 is likely to set another new all-time monthly record (until February 2015 … you get the idea.)

How do concentration measurements change in calendar years?  Let’s take a look at two charts that set that context up for us:

 photo CO2_concentration_5y_trend_NOAA_201312_zpse6bb2b3c.png

Figure 1 – Monthly CO2 concentration values (red) from 2009 through 2014 (NOAA). Monthly CO2 concentration values with seasonal cycle removed (black). Note the yearly minimum observation occurred three months ago (red curve) and the yearly maximum value occurred seven months ago. CO2 concentrations will increase through May 2014, as they do every year, before falling again towards this year’s minimum value.

This graph doesn’t look that threatening.  What’s the big deal about CO2 concentrations rising a couple of parts per million per year anyway?  The problem is the long-term rise in those concentrations and the increased heating they impart on our climate system.  Let’s take a longer view – say 50 years: photo CO2_concentration_50y_trend_NOAA_201312_zpscc6d916c.png

Figure 2 – 50 year time series of CO2 concentrations at Mauna Loa Observatory (NOAA).  The red curve represents the seasonal cycle based on monthly average values.  The black curve represents the data with the seasonal cycle removed to show the long-term trend (as in Figure 1).  This graph shows the relatively recent and ongoing increase in CO2 concentrations.

The big deal is, as a greenhouse gas, CO2 increases the radiative forcing toward the Earth, which over time 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 at a large-scale for some time.  Therefore, the general CO2 concentration rise in the figures above 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 3 – Historical CO2 concentrations from ice core proxies (blue and green curves) and direct observations made at Mauna Loa, Hawai’i (red curve).

This longer time series demonstrates how the curves in Figures 1 and 2 look when viewed against 10,000 additional years’ data.  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.  You can see this by the relatively small changes in concentration over many hundreds of years.  Recent concentrations are an obvious aberration to recent history.

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


Figure 4 – 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.  It is clear that our planet’s climate existed within a range of CO2 concentrations between 200 and 300 ppm over the past 800,000 years.  Indeed, you would have go back millions of years into the geologic history of the planet to find the last time CO2 concentrations were near 400 ppm.  And let me be clear, the global climate then was much different from today: the globe was much warmer, there were no polar ice caps, and ecosystems were radically different from today’s.  That’s not to say today’s climate is “better” or “worse” than a paleoclimate.  It is to say that today’s ecosystems do not exist in the climate humans are forcing on the planet.

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 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), not the lower emissions pathway.

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 and secondarily how effective CO2 removal in the future is.  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.


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