Weatherdem's Weblog

Bridging climate science, citizens, and policy

March 2013 CO2 Concentrations: 397.34 ppm

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During March 2013, the Scripps Institution of Oceanography measured an average of 397.34ppm CO2 concentration at their Mauna Loa, Hawai’i’s Observatory.

This value is a big deal.  Why?  Because not only is 397.34 ppm the largest CO2 concentration value for any March in recorded history, it is the largest CO2 concentration value in any month in recorded history.  More on that below.  This year’s March value is 2.89 ppm higher than March 2012′s!  Most month-to-month differences are between 1 and 2 ppm.  This jump of 2.89 ppm is very high, but is ~0.5 ppm less than February’s year-over-year change of 3.37 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.

Let’s get back to that all-time high concentration value.  The yearly maximum monthly value normally occurs during May. Last year was no different: the 396.78ppm concentration in May 2012 was the highest value reported last year and, prior to the last two months, in recorded history (neglecting proxy data).  We can expect April and May of this year to produce new record values.  I wrote the following two months ago:

If we extrapolate last year’s maximum value out in time, it will only be 2 years until Scripps reports 400ppm average concentration for a singular month (likely May 2014; I expect May 2013′s value will be ~398ppm).  Note that I previously wrote that this wouldn’t occur until 2015 – this means CO2 concentrations are another climate variable that is increasing faster than experts predicted just a short couple of years ago.

For the most part, I stand by that prediction.  But actual concentration increases might prove  me wrong.  Here is why: the difference in CO2 concentration values between May 2012 and March 2012 was 2.33 ppm (396.78 – 394.45).  If we do the simplest thing and add that same difference to this March’s value, we get 399.67 ppm.  That is awfully close to 400 ppm, but less than the 399.93 ppm extrapolation I performed last month.  I discussed May 2013’s projection with Sourabh after last month’s post.  They predicted 399.5-400 ppm concentration for May 2013.  I think NOAA will measure May 2013’s concentration near 399.3 ppm.  There are other calculations that we could do to come up with a range of predictions, but I unfortunately don’t have the time to do them right now.  I will have content myself with waiting until June to find out how fast concentrations rose through May.

I normally post’s chart of CO2 concentrations since 1958/59 for a given month.  They finally posted last month’s average concentration value yesterday, but have not updated their graph from February 2013 yet.  When they do, I will update this post.

[Update: here is their graphic for March 2013]

 photo co2_widget_brundtland_600_graph_201303_zpsd2636d06.gif

Figure 1 – Time series of CO2 concentrations measured at Scripp’s Mauna Loa Observatory in March from 1958 through 2013.

How do concentration measurements change in calendar years?  The following two graphs demonstrate this.

 photo CO2_concentration_5y_trend_NOAA_201304_zps58ea83d8.png

Figure 2 – Monthly CO2 concentration values from 2009 through 2013 (NOAA).  Note the yearly minimum observation is now in the past and we are two months removed from the yearly maximum value.  NOAA is likely to measure this year’s maximum value near 399ppm.

 photo CO2_concentration_50y_trend_NOAA_201304_zps6f791941.png

Figure 3 – 50 year time series of CO2 concentrations at Mauna Loa Observatory.  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.  This graph shows the recent and ongoing increase in CO2 concentrations.  Remember that as a greenhouse gas, CO2 increases the radiative forcing of the Earth, which increases the amount of energy in our climate system.

In previous posts on this topic, I showed and discussed historical and projected concentrations at this part of the post.  I will skip this for now because there is something about this data that I think provides a different context of the same conversation.  I saw a graphic last month that I provides useful focus on this topic:

 photo CO2_concentration_annual_growth_rate_NOAA_2012_zps4d9dfbcb.png

Figure 3 – CO2 concentration (top) and annual average growth rate (bottom). Source: Guardian

The top part of Figure 3 should look familiar – it’s the black line in Figure 3.  The bottom part is the annual change in CO2 concentrations.  If we fit a line to the data, the line would have a positive slope, which means annual changes are increasing with time.  So CO2 concentrations are increasing at an increasing rate – not a good trend with respect to minimizing future warming.  In the 1960s, concentrations increased at less than 1 ppm/year.  In the 2000s, concentrations increased at 2.07 ppm/year.  This isn’t surprising – CO2 emissions continue to increase decade after decade.  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.  Human systems do not yet exist that remove CO2 from any medium (air or water).  They are not likely to exist for some time.  So NOAA will extend the right side of the above graphs for years and decades to come.

The greenhouse effect details how these increasing concentrations will affect future temperatures.  The more GHGs (CO2 and others) are in the atmosphere, all else equal, the more radiative forcing the GHGs cause.  More forcing means warmer temperatures as energy is re-radiated back toward the Earth’s surface.  Conditions higher in the atmosphere affects this relationship, which is what my volcano post addressed.  A number of medium-sized volcanoes injected SO2 into the stratosphere (which is above the troposphere – where we live and our weather occurs) in the last decade.  Those SO2 particles reflected incoming solar radiation.  So while we emitted more GHGs into the troposphere, less radiation entered the troposphere in the past 10 years than the previous 10 years.  With less incoming radiation, the GHGs re-emitted less energy toward the surface of the Earth.  This is likely part of the reason why the global temperature trend leveled off in the 2000s after its relatively rapid run-up in previous decades.

This situation is important for the following reason.  Once the SO2 falls out of the atmosphere, the additional incoming radiation will encounter higher GHG concentrations than was present in the late 1990s.  As a result, we will likely see a stronger surface temperature response sometime in the future than the response of the 1990s.

The rise in CO2 concentrations will slow down, stop, and reverse when we decide it will.  We can choose 350 ppm or 450 ppm or any other target.  That choice is dependent on the type of policies we decide to implement.  It is our current policy to burn fossil fuels because doing so is cheap, albeit inefficient.  We will widely deploy clean sources of energy when they are cheap, which we control.  We will remove CO2 from the atmosphere when we have cheap and effective technologies and mechanisms to do so, which we control.  Today’s carbon markets are not the correct mechanism, as they are aptly demonstrating.  We will limit future warming and downstream climate effects when we choose to do so.


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