Could Ian Plimer be right or is he so far from the truth that he is off on another planet somewhere? [for those who need a Plimer Primer, his ICCC presentation is here, (video, audio coming soon); alternatively check out sympathetic and antagonistic reports of interviews with him]. I wasn’t familiar with his book before the conference and I enjoyed hearing him speak in Chicago: he was entertaining, he made me think and I enthused about what he said (more below). However, I got a blog comment that said:
“If you fancy yourself an intellectually honest person, you ought to read http://en.wikipedia.org/wiki/Talk:Ian_Plimer#Volcanoes_.26_CO2_section” [Update – this page of WP has now been replaced but a copy is here]
Now I’m used to hearing speculation from scientists at conferences; we often revel in it even when we secretly exchange glances with raised eyebrows and say “X was a bit far-fetched, but interesting if he was right”. Much of what Plimer said was just that – speculation that current estimates of CO2 emissions from volcanic activity are too low. He talked about what we don’t know and currently only estimate. His first bullet point conclusion was:
“Most major sources and sinks of CO2 [are] either ignored or grossly underestimated”
I read the Wikipedia editors’ discussion, for that’s what the link was, and you know what, it really enlightened me to the thinking behind Wikipedia. It also refers to consensus figure from US Geological Survey, which quotes total volcanic emissions of 130-230 million tonnes CO2/y , with human emissions coming in at 27 billion t/y. Still, I like to check facts for myself – since I haven’t read Plimer’s book and any research he might cite – is there recent published information that would up the volcanic emissions figure?
Well, I’ve done a bit of searching and a bit of reading. Most usefully I found a literature review  through Skeptical Science; although submitted in 1999/2000 it does provide an overview of a range of values, of which, for global volcanic CO2 flux, the reference used by USGS (Gerlach, 1991) is one of the lowest. The highest estimate is 367 Mt/y. This is based on both terrestrial and submarine volcanoes and includes eruptive and non-eruptive degassing (from craters, fissures and volcanic flanks). Non-eruptive degassing is generally regarded as underestimated.
Looking for more up-to-date estimates of degassing (not an exhaustive search however), I found a number of interesting references which either corroborate or provide upward estimates of regional degassing. For example a study in Iceland reported that, while two independent estimates of natural CO2 emissions range between 1 × 108 and 2 × 109 kg year−1, direct CO2 flux measurements from four of the approximately 40 geothermal/volcanic systems in the country amounted to 3 × 108 kg year−1, indicating that these estimates of the total natural flux may be too low . A 2007 study of CO2 degassing from a large area in central Italy also suggests previous underestimation. The total CO2 discharged from the study area was 0.9 × 1011 mol/y (just under 4 Mt/y), about five times higher than a previously published baseline value for terrestrial CO2 emissions .
I also found in the literature many instances of newly discovered submarine volcanic activity. One of the most spectacular was reported in June 2008 – a NASA and US National Science Foundation funded expedition explored part of the 1,800-kilometre-long Gakkel Ridge, which cuts across the Arctic from Greenland to Siberia . It is one of least accessible of the planet’s mid-ocean ridges where molten rock rises up from inside the earth creating new crust.
“The scale and magnitude of the explosive activity that we’re seeing here dwarfs anything we’ve seen on other mid-ocean ridges”
said Sohn, [a geophysicist from the Woods Hole Oceanographic Institute] who studies ridges around the world. The volume of gas and lava that appears to have blasted out of the Gakkel volcanoes is “much, much higher” than that seen at other ridges .
One reference that Plimer did cite was the ‘discovery’ (and upward estimate) of volcanic seamounts reported in 2007 . University of Cambridge scientists designed a computer programme that was able to analyse the huge amount of data in the sonar lines – some 40 million kilometres of linear profiles from research vessels that have been criss-crossing the oceans since the 1960s. The programme was able to identify volcano-like shapes in the data. They found evidence of 201,055 underwater cones, 10 times more than have been found before, and estimate that in total there could be about 3 million submarine volcanoes, 39,000 of which rise more than 1000 meters over the sea bed. We still know virtually nothing about the history and activity of most of these.
What about minerals? That was the other major thrust of the presentation – carbonate minerals – and how much of the Earth’s CO2 is locked up in them, produced from a variety of processes:
- submarine hydrothermal precipitates
- submarine basaltic alteration (ophiolite formation)
- igneous carbonate rock (carbonatites) 
- weathering of calcium and magnesium silicates as a sink for atmospheric CO2 
What Professor Plimer was actually saying was that natural geological production of CO2 was currently underestimated and that if we accounted for rates of CO2 production averaged over a more realistic geological time (our recent history being reasonably volcanically inactive) and added these to other natural sources, human CO2 production would pale into insignificance. So he talked about volcanoes and supervolcanoes and periods when areas such as the Deccan Traps spewed lava and CO2 in truly gargantuan quantities. Yes, we do live in relatively quiet times (fortunately) and major eruptions have been few in the past century, with even Pinatubo only emitting some 42 Mt of carbon dioxide in 1991. But averaged over time – geological time – volcanism is more important to the carbon cycle than current activity suggests.
Yes, a lot of what he said was hyperbole, but it is his opinion; after years of dry academic publications it must be fun to stand up and talk as he does. And you know what – I think Ian Plimer and his speculations are more firmly rooted on this planet that any of the wild forecasts of the IPCC models. But then you probably expected I would say that 😉
- Gerlach (1991) Present-day CO2 emissions from volcanoes. Eos, Transactions, American Geophysical Union, 72 (23):249 and 254-255.
- Mörner and Etiope (2002) Carbon degassing from the lithosphere. Global and Planetary Change 33:185–203
- Ármannsson et al., (2006) CO2 emissions from geothermal power plants and natural geothermal activity in Iceland. Geothermics 34(3):286-296
- Frondini et al., (2008) Carbon dioxide degassing from Tuscany and Northern Latium (Italy). Global and Planetary Change. 61(1-2):89-102
- Sohn, et. al. (2008) Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean. Nature 453:1236-1238
- Hillier and Watts (2007) Global distribution of seamounts from ship-track bathymetry data. Geophys. Res. Lett. 34:L13304
- Brady (1991) The effect of silicate weathering on global temperature and atmospheric CO2. J. Geophys. Res. 96:18,101-18,106.