The carbon balance of the earth is far less understood – or quantified – than “climate scientists” would have us believe. The two largest sources and sinks (forests and the oceans) are generally assumed to be largely in balance. Volcanoes are estimated to produce a very small amount of carbon dioxide. Carbon in rocks brought up from the deep mantle by tectonic activities are assumed to be in balance with the return of sediments and rocks into the deep mantle by subduction. These assumed balances of the big numbers means that the relatively small numbers for emissions from fossil fuel combustion and changing land use then become dominant in explaining the observed increase of carbon dioxide concentration in the atmosphere. But these assumptions include many uncertainties:
Carbon dioxide emission sources (GT CO2/year)
- Transpiration 440
- Release from oceans 330
- Fossil fuel combustion 26
- Changing land use 6
- Volcanoes and weathering 1
Carbon dioxide is accumulating in the atmosphere by about 15 GT CO2/ year. The accuracy of the amounts of carbon dioxide emitted by transpiration and by the oceans is no better than about 2 – 3% and that error band (+/- 20GT/year) is itself almost as large as the total amount of emissions from fossil fuels.
But it now appears that even the carbon dioxide emissions from volcanoes have been grossly underestimated. Not only have the emissions from erupting volcanoes been underestimated but it also seems that many volcanoes emit carbon dioxide almost continuously and invisibly (a diffuse degassing).
Volcanic CO2 Levels Are Staggering
Robin Wylie, University College London | October 15, 2013
…. Until the end of the 20th century, the academic consensus was that this volcanic output was tiny — a fiery speck against the colossal anthropogenic footprint. Recently, though, volcanologists have begun to reveal a hidden side to our leaking planet.
Exactly how much CO2 passes through the magmatic vents in our crust might be one of the most important questions that Earth science can answer. Volcanoes may have been overtaken in the carbon stakes, but in order to properly assess the consequences of human pollution, we need the reference point of the natural background. And we’re getting there; the last twenty years have seen huge steps in our understanding of how, and how much CO2 leaves the deep Earth. But at the same time, a disturbing pattern has been emerging.
In 1992, it was thought that volcanic degassing released something like 100 million tons of CO2 each year. Around the turn of the millennium, this figure was getting closer to 200. The most recent estimate, released this February, comes from a team led by Mike Burton, of the Italian National Institute of Geophysics and Volcanology – and it’s just shy of 600 million tons. It caps a staggering trend: A six-fold increase in just two decades. ……
….. As scientific progress is widening our perspective, the daunting outline of how little we really know about volcanoes is beginning to loom large. ….
…. We now know that the CO2 released during volcanic eruptions is almost insignificant compared with what happens after the camera crews get bored. The emissions that really matter are concealed. The silent, silvery plumes which are currently winding their way skyward above the 150 or so active volcanoes on our planet also carry with them the bulk of its carbon dioxide. Their coughing fits might catch the eye — but in between tantrums, the steady breathing of volcanoes quietly sheds upwards of a quarter of a billion tons of CO2 every year.
We think. Scientists’ best estimates, however, are based on an assumption. It might surprise you to learn that, well into the new century, of the 150 smokers I mentioned, almost 80 percent are still as mysterious, in terms of the quantity of CO2 they emit, as they were a generation ago: We’ve only actually measured 33.
If the 117 unsampled peaks follow a similar trend, then the research community’s current projection might stand. But looking through such a small window, there’s no way of knowing if what we have seen until now is typical or not. It’s like shining a light on a darkened globe: randomly, you might hit Australia, and think you’d seen it all – while on the edge of your beam, unnoticed, would be Asia. Our planet’s isolated volcanic frontiers could easily be hiding a monster or two; and with a bit of exploration, our estimate of volcanic CO2 output could rise even higher.
You’d think that would be enough. That might be my fault — I tend to save the weird stuff until the end. Recently, an enigmatic source of volcanic carbon has come to light that isn’t involved with lava — or even craters. It now seems that not only is there CO2 we can’t get to, there’s some we can’t even see.
Carbon dioxide is always invisible, but its presence can be inferred in volcanic plumes — betrayed by the billowing clouds of water vapour released alongside it. Without the water, though, it’s a different story. The new poster-child of planetary degassing is diffuse CO2 — invisible emanations which can occur across vast areas surrounding the main vents of a volcano, rising through the bulk of the mountains. This transparent haze is only just beginning to receive proper attention, and as such we have very little idea of how much it might contribute to the global output.
Even more incredibly, it even seems that some volcanoes which are considered inactive, in terms of their potential to ooze new land, can still make some serious additions to the atmosphere through diffuse CO2 release. Residual magma beneath dormant craters, though it might never reach the surface, can still ‘erupt’ gases from a distance. Amazingly, from what little scientists have measured, it looks like this process might give off as much as half the CO2 put out by fully active volcanoes.
If these additional ‘carbon-active’ volcanoes are included, the number of degassing peaks skyrockets to more than 500. Of which we’ve measured a grand total of nine percent.
Related: Deep Carbon Emissions from Volcanoes
Tags: Carbon cycle, carbon dioxide, global warming, volcanic carbon dioxide, Volcano
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