How do volcanoes contribute to climate change?

Volcanoes change the Earth’s climate by warming and cooling it. Their net effect on the climate is now small compared to that of pollutants of human origin.

Nonetheless, the climate change caused in prehistoric times by almost constant eruptions and, in recent centuries, by a handful of epic eruptions, gives a warning: it helps us imagine life on Earth if we let the environment be. ruined by our negligence.

Prehistoric volcanoes

The number of volcanic eruptions in recorded history is paltry in comparison to what scientists have discerned about volcanic activity in prehistoric times.

About 252 million years ago, in a vast expanse of what is now Siberia, volcanoes erupted regularly for about 100,000 years. (It might sound like a long time, but geologically it’s a snap.)

Volcanic gases and ash blown by the wind around the world have triggered a cascade of climate change. The result was a disastrous global biosphere collapse that killed up to 95% of all species on Earth. Geologists call this event the Great Die.

Volcanic disasters in historical times

Prior to 1815, Mount Tambora on the Indonesian island of Sumbawa was considered an extinct volcano. In April of that year it exploded – twice. Mount Tambora was once about 14,000 feet high. After his explosions, he was only about two-thirds his size.

The crater of Mount Tambora, about 200 years after its explosion.
Yus Iran / EyeEm / Getty Images

Most of the life on the island has been eradicated. Estimates of human deaths vary widely, from the 10,000 killed instantly, as reported in the Smithsonian Magazine, to the 92,000 that the United States Geological Survey (USGS) suggests died mostly of starvation after volcanic gas and ash ruined the city. land and changed the climate. With the exception of four lucky ones, the whole kingdom of Tambora (10,000 people) disappeared in the explosions.

With the rapid injection of ash and gas into the atmosphere, the monsoons in Asia developed more slowly, resulting in droughts that led to famine. The drought was followed by flooding which altered the microbial ecology of the Bay of Bengal. This appears to be what gave birth to a new variant of cholera and a global cholera pandemic. At the start of the 19th century, public health agencies were not coordinated, so it is difficult to determine the death toll from the pandemic. Non-final estimates put it in the tens of millions.

The following year, the global cooling induced by Tambora was so severe that 1816 is often referred to as the “year without summer” and the “Little Ice Age”. Snowstorms swept across North America and parts of Europe during the summer months, killing crops and livestock and causing famine, riots and a refugee crisis. The paintings of the year show dark and strangely colored skies.

Aside from Mount Tambora and a handful of other distressing volcanic disasters, things have not been as dramatic during historical times as they were during prehistoric times.

According to the USGS, along Earth’s ocean ridges where tectonic plates slide over each other under deep water, molten rock from the Earth’s superheated mantle is constantly rising from the depths of the Earth’s crust and creating a new ocean floor. Technically, all of the places along the ridge where incoming molten rock meets ocean water are volcanoes. Outside of these locations, there are approximately 1,500 potentially active volcanoes worldwide, and only 500 of them have erupted in recorded history. Their effects on the climate have been profound, but for the most part short-lived.

The basics of the volcano

The USGS defines volcanoes as openings in the earth’s crust through which ash, hot gases, and molten rock (aka “magma” and “lava”) escape as magma rises through the earth’s crust and emerges from the flanks or the summit of a mountain.

Some volcanoes discharge slowly, almost as if they are exhaling. For others, the rash is explosive. With deadly force and temperature, lava, pieces of solid rock on fire, and gases escape. (As an example of how much material a volcano can spew out, the National Oceanic and Atmospheric Administration (NOAA) estimates that Mount Tambora ejected 31 cubic miles of ash. Wired Magazine calculates that ash at this volume could “bury the entire playing surface of Fenway Park in Boston 81,544 miles (131,322 km) deep.”)

Mount Tambora was the largest eruption in recorded history. Even so, volcanoes in general spit out a parcel of ash. The gases too. When a mountain “blows” at its top, the ejected gases can reach the stratosphere, which is the layer of the atmosphere that extends from about 6 miles to 31 miles above the Earth’s surface.

Climatic effects of volcanic ash and gases

Mist of volcanic ash (“vog”).
Christine von Diepenbroek / Getty Images

While volcanoes overheat the surrounding air and warm temperatures locally while the mountain and its lava remain scorching, global cooling is the most prolonged and profound effect.

Global warming

One of the main gases released by volcanoes is carbon dioxide (CO2), which is also the man-made greenhouse gas most responsible for global warming on Earth. CO2 warms the climate by trapping heat. It allows short-wavelength solar radiation to pass through the atmosphere, but it does so while preventing about half of the resulting thermal energy (which is long-wavelength radiation) from escaping from it. Earth’s atmosphere and return to space.

The USGS estimates that volcanoes contribute about 260 million tonnes of CO2 to the atmosphere each year. Even so, the CO2 emitted by volcanoes probably has no significant effect on the climate.

NOAA estimates that humans poison the Earth’s atmosphere with 60 times more CO2 than volcanoes. The USGS suggests the difference is even greater; he reports that volcanoes release less than 1% of the CO2 that humans release, and that “the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming in the atmosphere.”

Global cooling, acid rain and ozone

As the winter consequences of Mount Tambora explosions have shown, the global cooling induced by volcanoes is a huge danger. Acid rain and the destruction of the ozone layer are other catastrophic effects of volcanoes.

Global cooling

Some gas : In addition to CO2, volcanic gases contain sulfur dioxide (SO2). According to the USGS, SO2 is the most important cause of global cooling of volcanic origin. SO2 turns into sulfuric acid (H2SO4), which condenses into fine droplets of sulfate that combine with volcanic vapor and create a whitish haze commonly referred to as “vog”. Blown around the world by the wind, the vog sends back into space almost all of the incoming solar rays that it encounters.

As much SO2 as volcanoes put into the stratosphere, the Environmental Protection Agency (EPA) labels the main source of SO2 haze as “the combustion of fossil fuels by power plants and other industrial facilities.” Hey, the volcanoes. You are relatively immune from this charge.

CO2 emissions of human and volcanic origin

  • Global volcanic emissions: 0.26 billion metric tons per year
  • Human-caused CO2 from fuel combustion (2015): 32.3 billion metric tons per year
  • Global road transport (2015): 5.8 billion tonnes per year
  • Eruption of Mount St. Helens, Washington State (1980, deadliest eruption in U.S. history): 0.01 billion metric tons
  • Mount Pinatubo eruption, Philippines (1991, second largest eruption in recorded history): 0.05 billion metric tons

* Source: United States Geological Survey

From the ash: Volcanoes throw tons of tiny fragments of rock, minerals and glass skyward. While the larger chunks of this “ash” fall fairly quickly from the atmosphere, the smaller ones rise into the stratosphere and stay at extremely high altitudes, where the wind blows them off. The millions or billions of tiny ash particles reflect incoming solar rays from Earth back to the sun, cooling Earth’s climate as long as the ash remains in the stratosphere.

Gas and ash working together: Geophysicists at several institutions in Boulder, Colorado, performed a climate simulation and compared their results with observations collected by satellite and aircraft after the tropical eruption of Mount Kelut in February 2014. They found that the persistence of SO2 in the The atmosphere depended significantly on had coated ash particles. More SO2 on the ash resulted in a more sustainable SO2 capable of cooling the climate.

Acid rain

One would imagine that an easy solution to global warming would be to intentionally infuse the stratosphere with SO2 to create cooling. However, hydrochloric acid (HCl) is present in the stratosphere. It is there because of the combustion of industrial coal on Earth and also because the volcanoes eject it.

When SO2, HCl, and water precipitate on Earth, they do so in the form of acid rain, which pulls nutrients from the soil and leaches aluminum in streams, killing many species of marine life. If scientists tried to counter global warming with SO2, it could wreak havoc.


Besides its potential to precipitate in the form of acid rain, volcanic HCl presents another danger: it threatens the Earth’s ozone layer, which protects the DNA of all plant and animal life from destruction by solar ultraviolet radiation without hinders. HCl quickly breaks down into chlorine (Cl) and chlorine monoxide (ClO). Cl destroys ozone. According to the EPA, “One atom of chlorine can destroy more than 100,000 molecules of ozone.”

Satellite data after volcanic eruptions in the Philippines and Chile showed a 15-20% loss of ozone in the stratosphere above volcanoes.

Takeaway meals

Aleksi Ilpala / Getty Images

Compared to human-made pollution, the contribution of volcanoes to climate change is low. The climate degrading CO2, SO2 and HCl in the Earth’s atmosphere are mostly the direct result of industrial processes. (Ash from coal combustion is primarily a lower land and air pollutant, and therefore its contribution to climate change may be limited.)

Despite the relatively insignificant role that volcanoes typically play in climate change, the floods, droughts, famine, and disease that have followed mega-volcanoes can serve as a warning sign. If human-caused air pollution continues unabated, floods, droughts, famines and disease could become unstoppable.

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