During April 2013, the Scripps Institution of Oceanography measured an average of 398.35ppm CO2 concentration at their Mauna Loa, Hawai’i’s Observatory.
This value is a big deal. Why? Because not only is 398.35 ppm the largest CO2 concentration value for any April in recorded history, it is the largest CO2 concentration value in any month in recorded history. More on that below. This year’s April value is 1.90 ppm higher than April 2012′s! Month-to-month differences typically range between 1 and 2 ppm. This jump of 1.90 ppm is within that range. It is also ~0.9 ppm less than March’s and 1.47 ppm less than February’s year-over-year change of 3.37 ppm. 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 three months, in recorded history (neglecting proxy data). I expect May of this year to produce another all-time record value. That value will hold first place until February 2014. I wrote the following three 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 in February. It’s also close to the 399.3 ppm extrapolation I calculated in March. I discussed May 2013′s projection with Sourabh after February’s post. They predicted 399.5-400 ppm concentration for May 2013. For the second month in a row, I think NOAA will measure May 2013′s mean concentration near 399.3 ppm.
Figure 1 – Time series of CO2 concentrations measured at Scripp’s Mauna Loa Observatory in April from 1958 through 2013.
CO2Now.org added the `350s` and `400s` to this month’s graphic. I suppose they’re meant to imply concentrations shattered 350 ppm back in the 1980s and are pushing up against 400 ppm now in the 2010s.
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 one month removed from the yearly maximum value. NOAA is likely to measure this year’s maximum value near 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 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:
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 (average rate of increase in the bottom graph by decade). 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. This happened because of their chemical and radiative properties. So while we emitted more GHGs into the troposphere, less radiation entered the troposphere (the bottom layer of the atmosphere) 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 remainder of the reason is the oceans. Thanks to the Interdecadal Pacific Oscillation’s most recent negative phase, the Pacific in particular absorbed heat energy near the surface and transported it to the deep ocean instead of allowing the heat to accumulate near the surface. The following graphic shows how heat absorption by global oceans changed in recent years:
Figure 5. New research that shows anomalous ocean heat energy locations since the late 1950s. The purple lines in the graph show how the heat content of the whole ocean has changed over the past five decades. The blue lines represent only the top 700 m and the grey lines are just the top 300 m. Source: Balmaseda et al., (2013)
This temporary energy transport to the deep ocean is good news in the short-term: global surface temperatures slowed their rise during the 2000s compared to the 1990s and 1980s. That does not mean however the global warming has stopped, as ideological skeptics want you to believe. That heat energy still exists in the Earth’s climate system. The oceans move heat around the planet just as the atmosphere does. The very large amount of extra heat currently in the deep ocean will eventually come back up to the surface. When it does, it add to the surface warming signal. So we can expect to see an extra rise of global mean surface temperatures sometime in the future. Thus, this is not good news in the long-term.
The rise in CO2 concentrations will slow down, stop, and reverse when we decide it will. It depends primarily on the rate at which we emit CO2 into the atmosphere. 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 we think doing so is cheap, albeit inefficient and without proper market signals. We will widely deploy clean sources of energy when they are cheap, the timing of which we control. We will remove CO2 from the atmosphere when we have cheap and effective technologies and mechanisms to do so, which we also control. 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. We will limit future warming and climate effects when we choose to do so.