A geological perspective on humanity: comparing human and volcanic CO2 emissions

I think this was my favorite paper this week.  It is both important, thoughtful and amusing (I think the author was trying to be dryly funny; but if not, my apologies).  Most of all, it's slightly mind-blowing.  I don't think my commentary enriches it, so below are simply my favorite quotes from it, with emphasis added. (Main figure at bottom)

Ultrashort summary: In order to emit CO2 at the same rate as humans, we would need Mt. St Helens to erupt violently every 2.5 hrs. 

[Update: Gerlach posted about this article on RealClimate here]
Terry Gerlach
Cascades Volcano Observatory (Emeritus), U.S.Geological Survey,Vancouver,Wash.

The climate change debate has revived and reinforced the belief, widespread among climate skeptics, that volcanoes emit more CO2 than human activities [Gerlach, 2010; Plimer, 2009]. In fact, present-day volcanoes emit relatively modest amounts of CO2, about as much annually as states like Florida, Michigan, and Ohio...

The projected 2010 anthropogenic CO2 emission rate of 35 gigatons per year is 135 times greater than the 0.26-gigaton-per-year preferred estimate for volcanoes....

Volcanic emissions include CO2 from erupting magma and from degassing of unerupted magma beneath volcanoes. Over time, they are a major source for restoring CO2 lost from the atmosphere and oceans by silicate weathering, carbonate depo- sition, and organic carbon burial [Ber- ner, 2004]. Global estimates of the annual present-day CO2 output of the Earth’s degas- sing subaerial and submarine volcanoes range from 0.13 to 0.44 billion metric tons (gigatons) per year [Gerlach, 1991; Allard, 1992; Varekamp et al., 1992; Sano and Wil- liams, 1996; Marty and Tolstikhin, 1998]; the preferred global estimates of the authors of these studies range from 0.15 to 0.26 gigaton per year....

Anthropogenic CO2 emissions—responsible for a projected 35 gigatons of CO2 in 2010 [Friedlingstein et al., 2010]— clearly dwarf all estimates of the annual present-day global volcanic CO2 emission rate. Indeed, volcanoes emit significantly less CO2 than land use changes (3.4 giga- tons per year), light-duty vehicles (3.0 giga- tons per year, mainly cars and pickup trucks), or cement production (1.4 gigatons per year). Instead, volcanic CO2 emissions are comparable in the human realm to the global CO2 emissions from flaring of waste gases (0.20 gigaton per year) or to the CO emissions of about 2 dozen full-capacity 1000-megawatt coal-fired power stations (0.22 gigaton per year), the latter of which constitute about 2% of the world’s coal-fired electricity-generating capacity. More meaningful, perhaps, are the comparable annual CO2 emissions of nations such as Pakistan (0.18 gigaton), Kazakhstan (0.25 gigaton), Poland (0.31 gigaton), and South Africa (0.44 gigaton)."

The nearly 9-hour duration of both the Mount St. Helens and Pinatubo paroxysms gives average CO2 emission rates of about 0.001 and 0.006 gigaton per hour, respectively. Intriguingly, the anthropogenic CO2 emission rate of 35 gigatons per year— equivalent to 0.004 gigaton per hour—is similar. So, for a few hours during paroxysms, individual volcanoes may emit about as much or more CO2 than human activities. But volcanic paroxysms are ephemeral, while anthropogenic CO2 is emitted relent- lessly from ubiquitous sources. On average, humanity’s ceaseless emissions release an amount of CO2 comparable to the 0.01 giga- ton of the 1980 Mount St. Helens paroxysm every 2.5 hours...

Several dilemmas arise from the belief that volcanic CO2 emissions exceed the 35-gigaton-per-year anthropogenic CO2 emis- sion. For example, a global volcanic CO2 output exceeding 35 gigatons per year would imply that the annual mass of volcanic CO2 emissions is more than 3 times greater than the likely annual mass of erupted magma (~10.8 gigatons per year [Crisp, 1984])... 
Scaling up all active subaerial volcanoes [to emit the same amount as humanity] evokes a landscape with the equivalent of about 9500 active present-day volcanoes...
Scaling up CO2 releases of volcanic paroxysms to the 35-gigaton anthropogenic CO2 emission level is also revealing. For example, scaling up the 0.05-gigaton CO2 release of the 15 June 1991 Mount Pinatubo paroxysm to the current anthropogenic CO2 emission level requires 700 equivalent paroxysms annually. Similarly, scaling the 0.01-gigaton CO2 release of the 18 May 1980 Mount St. Hel- ens paroxysm requires 3500 equivalent paroxysms annually...

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  1. Good work reporting such studies

  2. Been off my blogs for more than a year (mostly) just back. Thanks for the pointers on GW-CC.

  3. Sorry I did not mention one of my blog posts whereby I reference your work and upon which I have commentes in Fight Entropy: