Science counts humankind’s carbon output

Installing a gas monitor on a volcano in Papua New Guinea. Image: By Emma Liu, University of Cambridge, via Wikimedia Commons

We leave the planet’s volcanos far behind on greenhouse gas emissions: humankind’s carbon output can exceed theirs by 40 times – to our cost.

LONDON, 7 October, 2019 – Scientists now know how much carbon dioxide is pumped into the atmosphere and oceans by volcanos and volcanic fissures annually – perhaps as much as 360 million tonnes – and another crucial statistic, too: humankind’s carbon output.

They know that, by burning fossil fuels and clearing forests and building cities, we now emit much more than that: between 40 and 100 times more.

They can also now tell you how much carbon is in circulation above the Earth’s surface, in the oceans, on land, and in the atmosphere: the answer is 43,500 billion tonnes. That is about two-tenths of 1% of all the carbon locked for the moment in the Earth’s crust, mantle and core.

The research delivers no answers and no new directions for climate science, and in particular for governments and international agencies concerned about global heating and the climate emergency.

This is the ultimate in basic, bedrock, accounting: to understand the carbon cycle – the continuous traffic of carbon between atmosphere, ocean, rocks and living things – researchers need to have a better idea of the scale of what they like to call the carbon budget.

“To secure a sustainable future, it is of utmost importance that we understand Earth’s entire carbon cycle”

And after a decade of research, a partnership of more than 500 scientists from 39 countries working on more than 100 separate projects has delivered a set of down-to-earth answers in a new issue of the journal Elements.

The total estimate – it can only be an estimate – for the entire stock of carbon at the surface, in the crust and in the Earth’s mantle is around 1.85 billion billion tonnes.

And the observations of volcanic discharges of carbon are vital to understanding the cycle: this more or less steady renewal from deep below the surface is what has made life’s evolution from microbe to monkey puzzle-tree, from bacterium to Bactrian camel, possible over the last billion years.

Carbon from the atmosphere is absorbed by forests and sea meadows and buried, sometimes as shell and bone and limestone, sometimes as coal and oil and methane gas, and the carbon lost to the atmosphere is steadily replenished by deep hot sources from the Earth’s crust.

The study also highlights the nature of the climate emergency: by mining, drilling or quarrying for fossil fuels with which to drive chain saws through forests and bake limestone to make cement, humans are now returning ancient deposits of fossil carbon to the atmosphere at an overwhelming rate.

Doubling carbon levels

For most of human history, human ancestors, like all other life forms, evolved in a low-carbon atmosphere. In the past 60 years, humans have begun to double the normal levels of atmospheric carbon dioxide, a potent and enduring greenhouse gas.

And one pay-off of this increasingly urgent interest in the carbon cycle is that the researchers in the Deep Carbon Observatory partnership have added to fundamental knowledge and established what might be the limits of the knowable. They also have a better idea of carbon’s natural cycle.

“Carbon, the basis of all life and the energy source vital to humanity, moves through this planet from its mantle to the atmosphere. To secure a sustainable future, it is of utmost importance that we understand Earth’s entire carbon cycle,” said Marie Edmonds of the University of Cambridge, UK, one of the partnership.

“Key to unravelling the planet’s natural carbon cycle is quantifying how much carbon there is and where, how much moves – the flux – and how quickly, from Deep Earth reservoirs to the surface and back again.”

The Observatory recently identified the huge volume of subterranean life far below the planet’s surface. But the details of the carbon traffic in atmosphere, soils and waters are still somewhat muddy.

Only a start

The issue is vital to planning for what should be the accelerating shift from fossil fuels to solar and wind power, and researchers have been looking for new ways to assess vegetation uptake, the role of microbes in the world’s soils and the play between carbon and the world’s rivers.

The same study throws light on the periodic role of volcanic and magma discharges and other difficult-to-predict events in disrupting life on Earth. At least four times in the past 500 million years enormous discharges of carbon have changed climates and triggered mass extinctions.

And a giant meteor impact 66 million years ago is thought to have released up to 1400 billion tons of carbon dioxide, rapidly warmed the planet and helped in the mass extinction of plants and animals, including the dinosaurs.

The research continues: scientists will meet soon in Washington to start discussing the next decade of work.

“While we celebrate progress, we underline that deep Earth remains a highly unpredictable scientific frontier,” said Tobias Fischer of the University of New Mexico, another of the authors. “We have only truly started to dent current boundaries of our knowledge.” – Climate News Network