Talkshop readers with good memories may remember the article I wrote back in 2012 on findings by Cardellini et al that volcanic soils emitted far more CO2 than previously thought (and are not included in IPCC carbon cycle inventories). The implication is that longer sunshine hours during the 1980s-90s may well have released a lot of sequestered CO2 from these soils, thus raising atmospheric levels. Which would mean humans are not responsible for all of the increase, as has long been assumed.
Now another article from Robert Wylie on Livescience.com raises the issue again:
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 solarsystem, 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 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.