CSIRO Marine and Atmospheric Research

Volcanic eruptions and climate change
CSIRO Atmospheric Research Greenhouse Information Paper

A massive volcanic eruption can blast huge clouds of ash and gases into the atmosphere. Millions of tonnes of sulfur dioxide gas may reach the upper atmosphere (the stratosphere). There, the sulfur dioxide transforms into tiny particles of sulfuric acid, known as aerosol. The particles reflect energy from the sun back into space, preventing some of the sun's rays from heating the Earth.

This information paper examines the impact of volcanic eruptions on climate and the make-up of the atmosphere.

Surface cooling

Volcanic eruptions that add significant quantities of sulfur dioxide into the stratosphere lower global surface temperatures. Conversion of the sulfur dioxide to sulfuric acid aerosol in the stratosphere takes some months, so maximum cooling occurs up to a year after the eruption. It may take as long as seven years before the cooling influence of the volcanic aerosol disappears completely.

The 1991 eruption of Mt Pinatubo in the Philippines was one of the largest in the past 100 years. The injection into the stratosphere of 14-26 million tonnes of sulfur dioxide led to a global surface cooling of 0.5°C a year after the eruption. The climatic impact of the Pinatubo aerosol was stronger than the warming effects of either El Niño or human-induced greenhouse gas changes during 1991-93.

The observation of global surface cooling caused by the Mt Pinatubo eruption was successfully simulated by several global climate models, providing support for the effectiveness of models in replicating the climate system.

The eruption of Toba in Sumatra 73,500 years ago may have cooled the planet by 3-5°C, resulting in a ‘volcanic winter’.

As well as cooling the lower atmosphere (troposphere), volcanic aerosol can absorb both thermal radiation from the ground and solar radiation, which leads to a warming of the stratosphere above the tropics.

Volcanic eruptions need to be taken into account when using satellite measurements of temperature to detect trends caused by human activity. For example, once scientists had corrected the satellite temperature record to allow for the effects of volcanic eruptions and El Niño, the satellite measurements showed a small warming trend.

Global-mean monthly temperature for the period 1980-1999, showing the effects of the eruption of Mt Pinatubo in 1991. The upper graph shows the complete global-mean temperature record as context. (Source: University of East Anglia Climatic Research Unit: http://www.cru.uea.ac.uk/cru/info/causecc/)

Probability of eruptions

Eruptions of the scale of Mt Pinatubo occur roughly every 100 years. The impact of such eruptions needs to be taken into account when assessing long-term climate trends.

Eruptions are sporadic, unpredictable and vary in size. Ash and gases vary in composition. These factors present a challenge to climatologists seeking to isolate volcanic effects from other influences on past global climate.

There is a reasonably high probability that the temperature record will be influenced by volcanic activity in the next decade.

Gaseous emissions

Volcanoes are also sources of water vapour and carbon dioxide, but their contribution to the global budgets of greenhouse gases is very small. On the time-scale of decades to centuries, greenhouse gas emissions from volcanic sources cause negligible climate change.

However, volcanic emissions of gases such as sulfur dioxide, hydrogen sulfide and hydrogen fluoride are important compared to human-induced sources. These gases have effects on climate (cooling), on stratospheric ozone and possibly on global cloudiness.

Further reading

Robock, A., (1999) Volcanoes and climate, Reviews of Geophysics, 38(2), 191-219.

October 2000

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Modified: April 3, 2008

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