Highly anomalous terrain (an active volcano), 40 years of cooling temperatures, and a CO2 record that dramatically contrasts with fluctuating values from forests and meadows reaching 600-900 ppm all beg the question: Is Mauna Loa’s CO2 record globally representative?
Mauna Loa is the Earth’s largest land volcano. It has erupted over 3 dozen times since 1843, making this terrestrial landscape extremely unusual relative to the rest of the globe’s terrain. (Forests, in contrast, cover over 30% of the Earth’s land surface.)
Mauna Loa has been thought to be the world’s best location to monitor global CO2 levels since 1958.
While Mauna Loa CO2 levels show a rise of 338 ppm to 415 ppm since 1980, Mauna Loa temperatures (HCN) show a cooling trend during this same time period. The only warming period in the last 65 years occurred between about 1975 and 1985.
Image Source: oz4caster
Forest CO2 fluctuations
As mentioned above, forests are orders of magnitude more terrestrially representative than the highly anomalous site of the Earth’s largest volcano.
In forests or tree-covered areas, CO2 rises from around 300 ppm in the warmth of the afternoon (~3 p.m.) to over 600 ppm before sunrise (~4 a.m.), when it is cooler (Fennici, 1986, Hamacher et al., 1994). This massive fluctuation occurs daily and CO2 values average out to be far higher than the Mauna Loa record suggests.
Image Source: Fennici, 1986
Image Source: Hamacher et al., 1994
Meadow CO2 fluctuations
In open fields, or meadows, air CO2 can vary between 266 ppm and 1,430 ppm. The average variance is from 280 ppm to 980 ppm 2 meters above the soil (Szaran et al., 2005).
Interestingly, just as in forests, temperature drops of 4 to 5°C are associated with rising levels of CO2.
Image Source: Szaran et al., 2005
CO2 beneath snow and ice
Modern CO2 concentrations beneath snowpack and ice range from 600 to 1800 ppm. These concentrations can fluctuate by as much as 200 ppm within a period of just 4 days (Massman and Frank, 2006).
If this kind of rapid and wide-ranging variability can be observed for modern conditions, our capacity to accurately assess the “global” CO2 concentration for ice and snow thousands of years old becomes all the more suspect.
Image Source: Massman and Frank, 2006
CO2 near cave entrances
Within caves, CO2 levels can reach as high as 30,000 ppm. Even in the open air <1 meter from the entrance to a cave, CO2 levels can reach 11,500 ppm (Cowan et al., 2013).
CO2 levels vary by 10s of 1000s of ppm from one cave to the next in the same geographical region.
Image Source: Cowan et al., 2013
Mauna Loa CO2 is globally representative?
Cave entrances should probably be considered no less terrestrially unusual than the site of the world largest active volcano. And certainly forests and meadows are far more representative of the Earth’s terrestrial landscape than the Mauna Loa site.
And yet it has been decided, via consensus, that the rarified air above a Hawaiian island in the middle of the Pacific correctly monitors the CO2 levels for the entire globe.