UQx DENIAL101x 3.2.2.1 Human CO2 emissions trump volcanoes’
Channel: UQx Denial101x Making Sense of Climate Science Denial
Date: 15/08/2016

Andy Skuce examines how CO2 emissions from human activity compare to CO2 emissions from volcanoes and finds humans release much more.

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Extended commentary by Andy Skuce:
The main reference used in this lecture for emissions estimates from volcanoes is the 2013 review paper Deep Carbon Emissions from Volcanoes by Michael Burton, Georgina Sawyer and Domenico Graniero published in the journal Reviews in Mineralogy & Geochemistry Vol. 75 pp. 323-354, 2013. http://www.minsocam.org/msa/rim/RiMG075/RiMG075_Ch11.pdf
The figures I quoted in the talk are central estimate numbers quoted in Table 6 and there are considerable ranges of uncertainty associated with them. Table 7 shows how estimates of CO2 emissions form subaerial volcanoes have generally increased as research progresses over time. The lowest estimate (66 Mt/yr) was from Allard in 1992 and the highest (540 Mt/yr) –the one I used–was from the 2013 Burton paper.
Table 5 in Burton et al. shows a very wide range of CO2 emission estimates from different studies of mid-ocean ridge volcanoes of 4 to 792 Mt/yr, reflecting the difficulty of making these estimates. Burton et al. use a central estimate of 97 Mt/yr, which is what I adopted. That figure came from a study by Marty and Tolstikhin (1998) of 97 ± 40 Mt/yr of CO2.
I have also included sinks of CO2 that are associated with volcanic rocks. These amount to “ingassing” of approximately 180 Mt per year from weathering of volcanic rocks on land (Dessert et al., 2003) and 150 Mt/yr of CO2 from carbonation of volcanic rocks on the sea floor (Alt et al., 1999)
In case there are objections that the reactions that absorb CO2 should not be counted in the currently active volcanic emissions balance sheet, I have used both the gross emissions of 640 Mt/yr and the net emissions of 310 Mt/yr for comparisons with human emissions. Note that the volcanic gross emissions include significant current outgassing from inactive volcanoes, so that taking account of the uptake from current “ingassing” of volcanic rocks is consistent.
All of the data on human emissions and the historical CO2 concentration observations was downloaded from the Carbon Dioxide Information Analysis Center. The data were subject to minor computation (e.g., conversion of carbon masses to CO2 masses and cumulative emissions calculations) and the observations of concentrations were corrected to an 1850 baseline. The cumulative emissions were multiplied by 40% to make a rough estimate of the atmospheric fraction (the remainder of the CO2 being taken up by oceans and the terrestrial biosphere). This is not an exact method, since the take up of a pulse of CO2 is a complex time-dependent function arising from several independent processes. The simple 40% factor used here is for illustrative purposes only. The estimates in Table 10 in Le Quéré et al. (2014) yield an average atmospheric fraction of 42% since 1870, with a range of 37-48%. Most of the uncertainty arises from the estimates of land use CO2 emissions and terrestrial CO2 sinks.
There is more detail about these calculations and assumptions in a blogpost I wrote. https://critical-angle.net/2015/04/01/emissions-history-and-the-great-acceleration/
I performed a similar atmospheric concentration calculation assuming constant volcanic emissions of 310 and 640 Mt/yr. Human and volcanic emissions were then compared with observed atmospheric concentration changes since 1850, with the goal of showing how volcanic emissions are far too small to account for observations, whereas human emissions fit the observations closely, both in terms of magnitude and the shape of the atmospheric concentration curve.
I have used the term “dormant” volcano in an informal sense to mean a volcano that is no longer active but that may or may not become active in the future. Burton et al. used the term “inactive volcano”.

MYTH EXAMPLES
In case anybody thinks that I am flogging a dead horse in this lecture, below is a 2014 report of Alaska Senator Lisa Murkowski making the false claim and Mike Huebsch, an appointee of Wisconsin Governor Scott Walker making a similar assertion in 2015.
http://www.adn.com/alaska-beat/article/lisa-murkowski-and-volcano/2014/11/06/
http://www.huffingtonpost.com.au/entry/scott-walker-climate-change_n_7036766