Some Key Points
- There are other Greenhouse gasses but the concentration of Carbon dioxide (CO2) in our atmosphere is the key metric, measurements are taken at the Mauna Loa Observatory in Hawaii. It is a high altitude measurement in the well mixed troposphere in a pollution free environment.
- In September 2016 the level reached 400ppm, this was seen as key as it marks a point of no return in our lifetimes.
- The CO2 metric is an important metric as it is directly related to the global temperature deviation, as one increases the other generally follows.
- In the past 10 years CO2 levels in the atmosphere have increased by 35ppm, and given the status quo of 13% increases CO2 emission each decade we are likely to reach levels of 450ppm by 2030.
- The high/low projections to 2040 simply follows this trend in CO2 emissions, it is the nothing changes scenario.
Figure 5.1 shows the atmospheric CO2 record based on ice core data before 1958, (Ethridge et. al., 1996; MacFarling Meure et al., 2006) and yearly averages of direct observations from Mauna Loa and the South Pole after and including 1958 the units are ppm (parts per million). It is difficult to miss the huge increase since the beginning of the industrial revolution. A clever Swede called Arrhenius predicated in 1896 that the globe may warm with CO2 emissions however he thought it would take thousands of years to be a problem, since CO2 emission were much lower back then.
Half Our CO2 is reabsorbed - Figure 5.2
Analysing the persistence of atmospheric CO2 is complex, there is a time lag between emissions and temperature increase, and there is a natural half life of CO2 residence in the atmosphere. In Figure 5.2 we have plotted actual atmospheric CO2 levels, against a calculation* for CO2 levels where no emissions are reabsorbed by the planet, and against a case where they are all reabsorbed. With reference to the data showing temperature increase from 1980 where we see greater than 18Gt CO2 emissions, the data implies that the planet can take up to 18Gt or so of CO2 a year from human activity, but that anything above this will raise the temperature. However even this CO2 uptake is greater than the planet can handle without consequences for the land and the oceans for example ocean acidifications and the effect that has on sea life. It is not as simple as this but it serves as an approximation.
Figure 5.1 - Atmospheric CO2 record based on ice core data before 1958, (Ethridge et. al., 1996; MacFarling Meure et al., 2006) and yearly averages of direct observations from Mauna Loa and the South Pole after and including 1958 (ppm)
Figure 5.2 - Actual Atmospheric CO2 levels set against none reabsorbed by the planet and all reabsorbed by the planet (ppm)
The *calculation is very simple simple using a conversion from ppm to gigatonne of atmospheric carbon, the conversion tables of the Carbon Dioxide Information Analysis Center advise that 1 part per million of atmospheric CO2 is equivalent to 2.13 Gigatonnes atmospheric atmospheric carbon. This means 1ppm = 7.81 Gigatonnes of Carbon Dioxide (carbons atomic weight is 12 and the molecular weight of carbon dioxide is 44). Thus the two time series can both be plotted together and expressed as gigatonnes of carbon dioxide.