Volcanoes

Causes: Volcanoes

Ambrym Island, Vanuatu image: Sonny Whitelaw

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Summary

Volcanoes are a natural climate forcing. Over the last few hundred years, erupting volcanoes have caused global temperatures to drop slightly for short periods (Fig. 1). This because the erupt sulphur dioxide (SO₂), which reflects sunlight, cooling the atmosphere for up to 7 years.
Volcanoes do release some carbon dioxide (CO₂₎into the atmosphere. But in the last 200 years, they produced less than 2% compared to the amounts emitted from human activities. The evidence for this is the isotopic signature of CO₂ from volcanoes, which differs from the CO₂ isotope that comes from burning fossil fuels (Video 1).
At the end of the last glacial, melting glaciers may have triggered volcanic episodes (through isostatic rebound) that removed oxygen in the northeastern Pacific Ocean, explaining ‘dead zones’ that lasted millennia.
The eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano in 2022 damaged the ozone layer and sent huge quantities of water into the atmosphere. The net overall effect was a short-term cooling of the atmosphere, not warming.

It is estimated that the Hunga eruption cooled the global average surface air temperature (SAT) by 0.05 K, but this reduction is so subtle as to be indistinguishable from the natural variability of the current climate. – Stenchikov & Schoeberl 2025

Ancient mega-volcanoes and flood basalts, including the biggest ever volcanic outpouring in the history of the planet right under New Zealand, caused catastrophic climate changes implicated in all five of Earth’s mass extinction events (Videos 2 – 4).
Volcanoes have also been implicated in short-lived climate change events, including the so-called Little Ice Age in Europe.
Volcanoes also release water vapour into that stratosphere:

Stratospheric water vapour (SWV) is a key greenhouse gas that influences both global climate and stratospheric ozone chemistry – Peng et al 2026

Home > Climate wiki > What causes climate change? > Volcanoes

Summary

Volcanoes are a natural climate forcing. Over the last few hundred years, erupting volcanoes have caused global temperatures to drop slightly for short periods (Fig 1.).This is because they erupted sulphur dioxide (SO₂), which reflects sunlight, cooling the atmosphere for up to 7 years.
Volcanoes also release carbon dioxide (CO₂₎into the atmosphere. But in the last 200 years, they produced less than 2% compared to the amounts emitted from human activities. The evidence for this is the isotopic signature of CO₂ from volcanoes, which differs from the CO₂ isotope that comes from burning fossil fuels (Video 1).
At the end of the last glacial, melting glaciers may have triggered volcanic episodes (through isostatic rebound) that removed oxygen in the northeastern Pacific Ocean, explaining ‘dead zones’ that lasted millennia.
The eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano in January 2022 could eat away at ozone layer. It also sent huge quantities of water into the atmosphere. The net overall effect was a short-term cooling of the atmosphere, not warming.

Ancient mega-volcanoes and flood basalts including the biggest ever “volcanic outpouring” in the history of the planet right under New Zealand, caused catastrophic climate changes implicated in all five of Earth’s mass extinction events (Vidoes 2-4).
Volcanoes have also been implicated in short-lived climate change events, including the so-called Little Ice Age in Europe.
Volcanoes also release water vapour into that stratosphere:

Stratospheric water vapour (SWV) is a key greenhouse gas that influences both global climate and stratospheric ozone chemistry – Peng et al 2026

Impact of volcanoes on global temperatures 1815-2005
Figure 1: Volcanoes helped temporarily cool the climate

The impact of volcanoes on climate from1880 to 2005. The grey line shows rise in global temperatures during that period. Compare it with the orange line (volcanoes) and it’s clear that while the cooling effect of volcanic eruptions during this period temporarily offset some of the warming, it wasn’t enough to offset the rise in temperatures (Image: composite of graphs from Carbon Brief).
Figure 2: The cooling signature of major eruptions

Fig. 2: The comparative cooling impact of volcanoes on climate from1850-1991. (Image: Zeke Hausfather).

But don't volcanoes also release CO2?
Volcanoes make CO₂ by melting rocks underground, not by burning fossil fuels (combustion), which requires oxygen. Because carbon comes in three forms (isotopes): ¹²C, ¹³C, and ¹⁴C, and the levels of oxygen in the atmosphere are decreasing (Fig. 3), the chemical and isotopic signature in the atmosphere unequivocally points to humans, not volcanoes adding carbon dioxide to the atmosphere (Video 1).
Video 1: The different signatures of carbon dioxide

The quality of the video is not great, but Prof. Richard Alley explains in simple terms exactly how the isotopic signature of CO2 plus declining atmosphere O2 (less oxygen in Fig. 3) clearly points to humans burning fossil fuels.
Figure 3: The amount of oxygen in the atmopshere

How ancient volcanoes dramatically changed Earth's climate over billions of years
Some (but certainly not all) key volcanic eruptions that changed or helped change the climate:

When Earth formed 4.6 billion years ago, volcanoes erupted greenhouse gases methane and carbon dioxide. Along with other gases (but no oxygen yet) this created an atmosphere, which stopped Earth from completely freezing over.

2.4 billion years ago ‘Snowball Earth’ events—when ice covered most if not all of the planet some—ended when volcanoes erupted, increasing the amount of greenhouse gasses in the atmosphere (Video 2).
Video 2: How volcanoes took Earth from a 'Snowball' state into a warm state.
The ‘Great Dying‘: the Permian-Triassic extinction event. Around 252 million years ago a flood basalt eruption the size of Europe spewed lava over a vast area of Siberia in several waves for some 350,000 years (Video 3). Vast areas of carbon-rich rocks were melted and carbon dioxide poured into the atmosphere, resulting in rapid and catastrophic global warming, plus the loss of the ozone layer that led to intense DNA-stripping UV radiation. The video explains how flood basalt eruptions have led to several mass extinction events over hundreds of millions of years, and the role played by methane clathrates.

201.3 million years ago, a similar flood basalt eruption over ~11 million km² at the Central Atlantic Magmatic Province in North America, is implicated in the Triassic-Jurastic Extinction Event.
Video 3: Flood basalt eruptions
Around 120 million years ago, volcanic rock found beneath New Zealand’s North Island, and beneath the ocean floor near American Samoa, Tokelau and the Solomon Islands, were once joined together and may have originated from an outpouring of volcanic rock covering some 2000km across.(Video 3 @13 mins).

Some 66 million years ago, India was an island heading north towards Eurasia. As it travelled over a hotspot in the planet’s crust, a 20,000-year-long eruption of flood basalt and sulphur dioxide—a gas that reflects sunlight—in an area called the Deccan Traps, cooled the planet around 2°C. The first eruptions happened shortly before the comet that struck Earth and may have contributed to the extinction of the dinosaurs: the Cretaceous–Paleogene (K–Pg) extinction event. The comet may also have triggered more long term eruptions (Video 4) both from the Deccan Traps and also along the edges of plate boundaries under the ocean.
Video 4: Did a comet really take out the dinosaurs?

The comet blamed for killing the dinosaurs may have triggered more flood basalt eruptions that could have contributed to their extinction.
Ten million years later, some 55 million years ago, the boundary between the North American and European tectonic plates opened, leading to large scale eruptions that lasted over 20,0000 years. When tectonic plates separate, lava and gasses erupted from chasms hundreds of kilometres long, melting carbon-rich rocks, something that still happens in Iceland today (Fig. 4). So much CO₂ entered the atmosphere that global temperatures rose some 6°C within 20,000 years—geologically a very short time.

This period, the Palaeocene/Eocene Thermal Maximum (PETM), was the largest mass extinction event in the ocean in the past 93 million years—worse than the extinction event that wiped out the dinosaurs.
Figure 4: Fissure eruption, Iceland

Image: Reykjavik Helicopters
Seventy-five thousand years ago the super-volcano Toba in Indonesia erupted. Earth was already in the current Ice Age. The eruption caused a ‘volcanic winter’ that lasted 6-10 years, followed by 1,000 years of colder weather and more intense glaciation (Video 5).
Video 5: Toba
A series of volcanic eruptions from the 11^th to 19^th centuries were thought to have contributed to but not solely responsible for the so-called ‘Little Ice Age’. These volcanoes include but are not limited to:
1257 Samalas (Indonesia)

1452 Kuwai (Vanuatu)

1589 Billy Mitchel (Papua New Guinea)

1600 Huaynaputina (Peru)

1783 Laki (Iceland)

1814 Mayon (Philippines)

1815 Tambora (Indonesia)

1831 Zavaritskii (Kuril islands/Russia)

More information

Explainer: What is 'isostatic rebound'

Also known as crustal rebound, happens when the huge weight of ice sheets is removed, and the lithosphere lifts upwards in response (rebounds).

When such a large weight is removed from areas where tectonic plates collide, such as the NW Pacific ans Aotearoa, can result in more earthquakes and volcanic activity as the land readjusts upwards.

The full rebound happens over many thousands of years, and is still happening in parts of North America and Europe. The speed of this rebound, while slow, needs to be taken into account when calculating the vulnerability of coastlines to rising sea levels.

Explainer: What are climate 'forcings'?

The term ‘climate forcing’ comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy reaching Earth’s atmosphere and the amount that escapes. If more solar energy escapes than arrives, the planet cools. Conversely, if less energy escapes than gets in, the planet warms.

Click here to learn about the main forcings and how they work (links to a page on this site).

Explainer: Why coal, oil and gas are called 'fossil' fuels

Fossil fuels are literally the carbon in plants and animals that died millions of years ago. As the conditions that made them no longer exist, they cannot be replaced (at least in anything remotely relevant to human lifespans), so they are non-renewable.

Take coal for example. This comes from trees that grew in vast lowland swamp forests during the (appropriately named) Carboniferous Period, 358.9 million years ago (Mya), to 298.9 Mya. The high levels of carbon dioxide and even higher levels of oxygen in the atmosphere during that period plus the collision of continents that created low lying land and a hot wet climate, were the perfect conditions over millions of years for dead trees to fall into swampy ground. Here, they couldn’t be decomposed through normal processes. Instead, they turned into peat and eventually became the ‘fossil’ fuel coal. (See the carbon cycle on this website for more details and how oil and gas was made).

Today, burning this coal is releasing the carbon back into the atmosphere as carbon dioxide (CO₂₎_.

Explainer: Mass extinction events

Explainer: The Little Ice Age

This is generally regarded as the period 1300 – 1850AD. Several forcings appeared to have contributed, including the 1257 eruption of Samalas volcano. The AMOC (Atlantic oceanic current) also seems to have slowed due to a sudden influx of freshwater following the ‘Medieval Warm Period’ 950-1250AD. A part of this current, the Gulf Stream, is crucial for keeping Europe warm. Slight changes have global impacts, which is why it’s a concern today, as the current is slowing down.

A very small contribution to the cooling may have been from a slight decline in solar radiation. However, the Maunder Minimum didn’t begin until 1645AD (Fig. 4) three hundred years after cooling began in the Northern Hemisphere.

A very small contribution may have been from a slight decline solar radiation. However, the Maunder Minimum didn’t begin until 1645AD (Fig. 4; see Sunspots and Solar activity), three hundred years after cooling began in the Northern Hemisphere.

Actual ice ages: we’re currently living in the Quaternary Period, an Ice Age. Confused? Don’t be. This page explains the difference between ice ages (Periods) and glacials (epochs).

Explainer: Tambora

The year after Tambora erupted, 1816, was known in Europe as the ‘Year without summer’. Temperatures dropped 0.53°C in the Northern Hemisphere. However it wasn’t a global ‘climate change’ event; the effect on the Southern Hemisphere wasn’t as noticeable.

References and further reading
2026: Peng et al; Moderate volcanic eruptions and extreme wildfires humidify the stratosphere, Nature article 01 July

2025: APARC Report No. 11; The Hunga Volcanic Eruption Atmospheric Impacts Report

2024: Hutchison et al; The 1831 CE mystery eruption identified as Zavaritskii caldera, Simushir Island (Kurils), PNAS 122 | 1

2025 Plain English explanation (Physics.org)

2024: Schoeberi et al; Evolution of the Climate Forcing During the Two Years after the Hunga Tonga-Hunga Ha’apai Eruption, ESS Open Archive

NASA: What do volcanoes have to do with climate change?

Carbon Brief: Why scientists think 100% of global warming is due to humans

Accuweather: How massive volcano eruptions can alter global temperatures

2022: Du et al; Volcanic trigger of ocean deoxygenation during Cordilleran ice sheet retreat, Nature 611 pp74-80

2022: Scharping, Massive undersea eruption filled atmosphere with water, Science, 27 July

2020: Recent paleoclimate publications

2020: Stern et al; High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes, Science Advances 6/22

2020: Voosen; No asteroids needed: ancient mass extinction tied to ozone loss, warming climate, Science

2019: Voosen; Did volcanic eruptions help kill off the dinosaurs? Science (editorial article) Feb 21

2019: Zambri et al; Modeling the 1783–1784 Laki Eruption in Iceland: 2. Climate Impacts, JGR Atmospheres, 124 | 13 pp 6770-6790

2017: Gutjahr et al, Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum. Nature 548 (7669)

2016: Gernon et al; Snowball Earth ocean chemistry driven by extensive ridge volcanism during Rodinia breakup; Nature Geoscience 9, 242-248

2015: Rene et al; State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact: Science 350 (6256) 76-78

2013 IPPC: Chapter 8: Anthropogenic and Natural Radiative Forcing in: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

2013: Rathi; Indonesia’s Samalas volcano may have kickstarted the Little Ice Age, The Conversation

2008: Wtize; The volcano that changed the world, Nature news article.

2007: Storey et al; Paleocene–Eocene Thermal Maximum and the opening of the Northeast Atlantic; Science 316 587-589

2007: Nemeth et al; Kuwae Caldera and Climate Confusion, The Open Geology Journal 107(1):7-11

2004 Pierrehumbert: High levels of atmospheric carbon dioxide necessary for the termination of global glaciation Nature 429, 646–649

2004: Svensen et al; Release of methane from a volcanic basin as a mechanism for initial Eocene global warming: Nature 429 542-545

2001: Atwell; Volcanism and Short-Term Climatic Change in East Asian and World History, c. 1200-1699, Journal of World History 12|1 pp29-98

2001: Mirabueno: Reconstruction of the 01 February 1814 eruption of Mayon Volcano, Philippines. Masters thesis, University of Canterbury