Volcanoes play their own role in warming Earth: Study

It also found that all volcanoes on the planet are emitting carbon dioxide

By Shagun
Published: Tuesday 01 October 2019

All of Earth’s volcanoes are emitting carbon dioxide (CO2) and have played their own role in warming the planet, despite humanity’s emissions in the past 100 years exceeding them greatly, experts have said.

Scientists at the Deep Carbon Observatory (DCO) have found that even a handful of volcanic events have caused catastrophic releases of carbon, leading to a warmer atmosphere, acidified oceans, and mass extinctions.

DCO is a 10-year global research collaboration of more than 1,000 scientists to understand the quantities, movements, forms, and origins of carbon in Earth.

Researchers from DCO's DECADE (Deep Earth Carbon Degassing) subgroup found that volcanoes and volcanic regions outgassed (release of trapped gaseous material) an estimated 280-360 million tonnes (0.28 to 0.36 Gigatonnes or Gt) of CO2 per year.

This includes the contribution from active volcanic vents, from the diffusing and widespread release of CO2 through soils, faults, and fractures in volcanic regions, volcanic lakes, and from the mid-ocean ridge system.

Contrast that with humanity’s role in producing emissions. For the past 100 years, humanity’s annual carbon emissions through the burning of fossil fuels and forests were 40 to 100 times greater than those from geologic sources such as all volcanic emissions, said DECADE.

About 400 of the 1500 volcanoes active since the last Ice Age 11,700 years ago are venting CO2 today, said DECADE.

Another 670 could be producing diffuse emissions, with 102 already documented. Of these, 22 ancient volcanoes that have not erupted since the Pleistocene Epoch (2.5 million years ago to the Ice Age) are outgassing.

DECADE also confirmed that more than 200 volcanic systems emitted measurable volumes of CO2 between 2005 and 2017. Of these, several regions of degassing have been documented. These include Yellowstone in the United States, the East African Rift, and the Technong volcanic province in China.

The Earth's total annual outgassing of CO2 via volcanoes and through other geological processes such as the heating of limestone in mountain belts is estimated by DCO experts at roughly 300 to 400 million metric tonnes (0.3 to 0.4 Gt).

A fine balance

The quantity of carbon released from Earth's mantle has been in relative balance, the experts said, with the quantity returned through the downward subduction of tectonic plates and other processes.

However, this balance has been upended about four times over the past 500 million years by the emergence of large volcanic events — one million or more square kilometres (the area of Canada) of magma released within a timeframe of a few tens of thousands of years up to one million years.

These ‘large igneous provinces’ degassed enormous volumes of carbon (estimated at up to 30,000 Gt — equal to about 70 per cent of the estimated 43,500 gt of carbon above the surface today).

Any imbalance to the carbon cycle could cause rapid global warming, changes to the silicate weathering rate, changes to the hydrologic cycle, and overall rapid habitat changes that could cause mass extinction as the earth rebalanced itself, the report by the scientists warned.

The scientists also calculated that just two-tenths of one per cent of Earth's total carbon — about 43,500 Gt — is above surface in the oceans, on land, and in the atmosphere. The rest is subsurface, including the crust, mantle and core — an estimated 1.85 billion Gt in all.  

The findings are part of estimations by the DCO scientists of the Earth's immense interior carbon reservoirs, and how much carbon the deep Earth naturally swallows and exhales.

While around 37,000 gt carbon (85.1 per cent) is in the deep ocean, 3,000 gt (6.9 per cent) lies in marine sediments.

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