Mauna Loa & Mount Semeru volcanoes erupted within a week. Will they impact global climate?

Greenhouse gas emissions from the two eruptions very small compared to CO2 emissions from fossil fuel burning  

By Rohini Krishnamurthy
Published: Tuesday 06 December 2022

Two major volcanoes — Mauna Loa in Hawaii and Mount Semeru in Indonesia — erupted in a span of a week, releasing plumes of gases such as carbon dioxide (CO2) and sulphur dioxide (SO2) into the atmosphere. 

But the CO2 emitted is unlikely to impact the global carbon budget, Tobias Fischer, Professor at the University of New Mexico, told Down To Earth.

Mauna Loa in Hawaii erupted November 28, 2022, after a 38-year-long gap. Mount Semeru exploded on December 4, after a year.

“Even though Mauna Loa produces about 180,000 tonnes of SO2 per day and probably about 90,000 tonnes per day of CO2, these emissions are very small compared to the daily CO2 emissions produced by burning fossil fuels,” he added.

In 2022, the world recorded 25 new volcanic eruptions, according to the Global Volcanism Program, a database distributed by Smithsonian Institution. In 2021, 33 new eruptions occurred.

Volcanoes emit plumes of gases and ash during an eruption. About 99 per cent of the gas molecules emitted during a volcanic eruption are water vapour, CO2 and SO2, according to the United States Geological Survey.

Prehistoric volcanic eruptions have been linked to mass extinctions. For example, the Siberian Traps — remnants of widespread volcanic activity about 250 million years ago — are thought to have triggered the ‘Great Dying’ or the end-Permian extinction.  

The eruption released toxic volumes of greenhouse gases into the atmosphere, raising air and sea temperatures. It wiped out some 96 per cent of marine species and 70 per cent of terrestrial species, according to scientists.

The lava covered an area the size of Western Europe and was more than a kilometre thick, according to the University of California, Berkeley.

Scientists speculate that steady pulses of lava from massive fissures and vents in Earth over hundreds of thousands of years can generate much more lava and affect vast areas, covering millions of square kilometres.

This pales in comparison with the recent volcanic activities, where a mountain erupts, spewing lava.

Human contribution to the carbon cycle is more than 100 times those from all the volcanoes in the world combined, the US National Aeronautics and Space Administration (NASA) estimated

Recent CO2 emissions from the 2014 Holuhraun eruption in Iceland, the 2006 Etna Volcano in Italy and 2010 Eyjafjallajökull eruption in Iceland have released a cumulative of 9,330 kilo-tonnes, 644 kilo-tonnes and 5,130 kilo-tonnes of CO2 respectively. 

In contrast, human activities such as fossil fuel burning and cement production released 36.3 gigatonnes of CO2 into the atmosphere in 2015, according to the Global Carbon Budget 2016.

Therefore, according to Fischer, the largest CO2-emitting eruption in the past 15 years produced only about 0.026 per cent of the yearly anthropogenic emissions. 

Also, not all volcanoes release the same amount of CO2, as this depends on the CO2 content of the magma moving up to the surface. It also relies on how much gases escape out of the magma during an eruption, the expert explained. 

“As a thumb rule, volcanoes in hot spots such as Hawaii, Iceland or the Canary Islands tend to be more effusive and emit more CO2 than those in subduction zones such as Semeru,” Fischer said.

In effusive volcanoes, magma flows with less resistance, allowing gases to escape easily, the British Geological Survey noted.

In explosive volcanoes, magma erupts rapidly out of the volcano as pressure builds. They can give rise to pyroclastic flows, which contain rock fragments and gases moving downhill under gravity. They have a temperature range of 200-700 degrees Celsius and can destroy everything in their path.

Mount Semeru, an explosive volcano, produced pyroclastic flows. Some reached at least eight miles from the volcano’s peak, Robin George Andrews, an expert on volcanoes, wrote on Twitter.

The eruption appears to be less severe than Tonga, the underwater volcano which erupted on January 15, 2022. Tonga generated pyroclastic flows, which travelled 50 miles from their source, Andrews added.

Global cooling?

Scientists also measure SO2 since it has a global cooling effect. After the 1991 Mount Pinatubo explosion in the Philippines, for instance, researchers recorded a 0.5 °C drop in the average global temperature over large parts of Earth from 1992 through 1993. The total mass of SO2 in the volcanic cloud was 20 teragrams.

Mauna Loa released roughly 0.2 teragrams of SO2 on November 28. In 1984, it was estimated to have emitted around 1.2 teragrams SO2, Simon Carn, professor at Michigan Technological University, wrote on Twitter.

Tonga released roughly 0.4-0.5 teragrams SO2. This is low compared to other eruptions of similar magnitude, a pre-print study showed.

Read more: Can a large volcanic eruption slow down global warming? Here’s what the latest IPCC report says

One study simulated SO2 emissions from over 90 volcanoes. Roughly 3 teragrams of SO2 was released per year on an average in the last decade.

SO2 reacts with water to form sulphuric acid droplets, which become part of aerosol particles. 

Aerosols are tiny liquid droplets suspended in the air. The sulphur aerosols can scatter and absorb incoming sunlight, NASA said.

An explosive volcanic eruption could occur in the 21st century, the Sixth Assessment Report of the Intergovernmental Panel on Climate Change suggested.

This eruption could lower surface temperature and precipitation globally, especially over land, for one to three years. “If such an eruption occurs, it would therefore temporarily and partially mask human-caused climate change,” the report added.

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