Long Invisible, Research Shows Volcanic CO2 Levels Are Staggering

  • Date: 04/07/14
  • Robin Wylie, University College London, Life Science

The exploding hills really give the game away: We’ve always known the Earth is a smoker. The true extent of its habit, though, is only just beginning to surface.

Before the human species found its talent for pyromania, atmospheric levels of the Earth’s greenhouse superstar, carbon dioxide (CO2), were controlled, for the most part, by volcanoes.

Since our planet emerged from the debris which formed the solar system, some four and a half billion years ago, a lifetime supply of primordial carbon has been locked away in the mantle — against its will. Partnering with oxygen and smuggled as a dissolved gas in liquid rock, it breaches the surface at our planet’s volcanic airways: CO2, then, has been seeping into the planet’s atmosphere for as long as there has been one.

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 COleaves 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 COeach year. Around the turn of the millennium, this figure was getting closer to 200. The most recent estimate,releasedthis 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.

These inflating figures, I hasten to add, don’t mean that our planet is suddenly venting more CO2.

Humanity certainly is; but any changes to the volcanic background level would occur over generations, not years. The rise we’re seeing now, therefore, must have been there all along: As scientific progress is widening our perspective, the daunting outline of how little we really know about volcanoes is beginning to loom large.

Quiet monsters

The exhalations of our planet can be spectacularly obvious. The fireworks, though, are only part of the picture. 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.

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