During February 2013, the Scripps Institution of Oceanography measured an average of 396.80ppm CO2 concentration at their Mauna Loa, Hawai’i’s Observatory.
This value is a big deal. Why? Because not only is 396.80 ppm the largest CO2 concentration value for any February in recorded history, it is the largest CO2 concentration value in any month in recorded history. More on that below. This year’s February value is 3.37 ppm higher than February 2012′s! Most month-to-month differences are between 1 and 2 ppm. This jump of 3.37 ppm is very high. 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 this moth, in recorded history (neglecting proxy data). We can expect March, April, and May of this year to produce new record values. I wrote the following last month:
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 February 2012 was 3.13 ppm (396.78 – 393.65). If we do the simplest thing and add that same difference to February’s value, we get 399.93 ppm. That is awfully close to 400 ppm. A more robust approach would be to add an average value – say the annual growth rate from the past 3, 5, or 10 years. Over those time periods, the average differences are 2.31 ppm, 2.08 ppm, and 2.08 ppm. So it’s probably safe to assume a growth of at least 2 ppm, which is what I did in my original prediction. 396.78 ppm + 2 ppm = 398.78 ppm (2013′s prediction). 398.78 ppm + 2 ppm = 400.78 ppm (2014′s prediction). But if we use annual averages, we smooth out the large jumps in concentration values (like the 2013-2012 February difference). 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. We will have to be content with waiting until early June to find out how fast concentrations are rising this year.
It is worth noting here that stations measured 400ppm CO2 concentration for the first time in the Arctic last year. The Mauna Loa observations are usually closer to globally averaged values than other sites, such as in the Arctic. That is why scientists and media reference the Mauna Loa observations most often.
Figure 1 – Time series of CO2 concentrations measured at Scripp’s Mauna Loa Observatory in February: from 1959 through 2012.
This time series chart shows concentrations for the month of January in the Scripps dataset going back to 1959. As I wrote above, concentrations are persistently and inexorably moving upward. How do concentration measurements change in calendar years? The following two graphs demonstrate this.
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 between 398ppm and 399ppm.
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 toward the Earth, which eventually increases tropospheric temperatures.
In previous posts on this topic, I show and discuss 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. The increase in average annual concentrations in 2012 generated quite a bit of buzz in media outlets this week. I dismissed the first couple of reports I saw because I’ve spent so much time during the past year writing about the concentrations. But more media outlets wrote and discussed the same topic as the week went on. So I think it is a valid story, especially after I saw a graphic that I thought should have been the focus the entire time:
Figure 4 – CO2 concentration (top) and annual average growth rate (bottom). Source: Guardian
The top part of Figure 4 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.
The greenhouse effect details how these concentrations will affect future temperatures. The more GHGs 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). Those SO2 particles reflect 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 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 interact with higher GHG concentrations than was present in the late 1990s. We will likely see a strong surface temperature response sometime in the future.
In my mind, the newsworthy detail is not that CO2 concentrations increased at the second fastest rate on record in 2012. In climate, year-to-year differences matter less than long-term trends. In my mind, the decadal concentration increase is what is noteworthy. If concentrations rise by an average of >3 ppm/year in the 2010s or 2020s, a great deal of future warming and other climate change effects will occur.
It is my opinion that global temperature rise by 2100 will exceed 2C. This target is primarily politically-driven. Scientific research doesn’t exist that dictates 2C is “safe”. Scientific research does exist that projects the likely temperature response to a range of CO2 concentration values. If we do want to prevent >2C global temperature rise by 2100, we would have to immediately stop emitting CO2 and begin removing CO2 from the atmosphere. We currently don’t have technologies to do either.
I have more to say about some details in the Guardian article from which I got Figure 4. That will have to wait for another post. The Science study the article mentions is worthy of discussion, as is the Guardian’s comment that concentrations continue to increase despite government action. The article also links to a recent study of GHG reductions by 2020. I will address these in an upcoming post.