Volcanic Activity and Global Warming

There is considerable evidence to suggest that large volcanic eruptions have extensive effects on our global climate.

Firstly, consider the vast quantity of carbon dioxide volcanic eruptions produce, a gas known to contribute to the greenhouse effect. The greenhouse effect is essential for our survival as it maintains the temperature of our planet within habitable range. Such greenhouse gases trap heat radiated off the earth’s surface, forming a type of insulation around the planet.

The earth receives heat from the sun and loses heat by reflecting it back into the atmosphere. The atmosphere contains a mixture of gases that trap heat and keep the earth’s surface warm. These greenhouse gases (water vapor, carbon dioxide, methane, nitrous oxide and ozone) are vital for life on earth. If they didn’t exist it is likely that earth would be too cold to sustain life. Due to our energy intensive lifestyles and the burning of vast quantities of fossil fuels the levels of greenhouse gases have been increasing rapidly which magnifies the greenhouse effect and traps more and more heat close to the earth’s surface.

There is well documented data that provides a high degree of confirmation that man made production of gases such as carbon dioxide from the burning of fossil fuels may be testing the systems boundaries a little too much, resulting in excessive warming on a global scale.

Although there may be a debate ongoing in relation to climate science and the contribution of man made global warming, it is generally accepted that volcanic eruptions add carbon dioxide to the atmosphere, however, when compared to quantity of carbon dioxide produced by human activities, their impact seems marginal: volcanic eruptions generate around 110 million tons of carbon dioxide each year, in comparison to human activities which contribute almost 10,000 times that quantity.

May 18, 1980, Mount St. Helens eruption. Image Credit: USGS/Cascades Volcano Observatory, Vancouver, Washington

Karen Harpp, an assistant professor of geology at Colgate University, suggests that the more substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns add ash particles and sulphur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of volcanic activity. The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. The sulphurous gases then combine with water in the atmosphere to form acidic aerosols that additionally absorb incoming solar radiation and scatter it back out into space.

Initially, scientists believed that the volcanoes’ stratospheric ash cloud had the dominant effect on global temperatures. However, the eruption of El Chichon in Mexico 1982 altered this perception. Two years prior, the eruption of Mount St Helens had lowered global temperatures by about 0.1 degrees Celsius. Contrastingly, the smaller eruption of El Chichon, had three to five times the global cooling effect worldwide. Despite its smaller ash cloud, El Chichon emitted more than 40 times the volume of sulphur-rich gases produced by Mount St Helens, thus revealing that the formation of atmospheric sulphur aerosols had a more substantial effect on global temperatures than simply the volume of ash produced during an eruption.

The atmospheric effects of volcanic eruptions were confirmed following the 1991 eruption of Mount Pinatubo, in the Philippines. Pinatubo’s eruption cloud exceeded to reach 40 kilometres into the atmosphere and expelled around 17 million tons of sulphur dioxide (just over twice that of El Chichon).

The sulphur-rich aerosols circled the globe, producing a global cooling effect approximately twice that of El Chichon, with the northern hemisphere cooling by up to 0.6 degrees Celsius during 1992 and 1993. Furthermore, it is believed the aerosol particles may have played a part contributing to an accelerated rate of ozone depletion during that same period. Interestingly, some scientists argue that without the cooling effect of major volcanic eruptions such as El Chichon and Mount Pinatubo, global warming effects caused by human activities could have been far more widespread.

Georgiy Stenchikov, research professor with the Department of Environmental Sciences at Rutgers University stated, “Volcanic eruptions cause short-term climatic changes and contribute to natural climate variability”. Furthermore, he added that “exploring the effects of volcanic eruptions allow us to better understand important physical mechanisms in the climate system that are initiated by volcanic forcing”. Stenchikov and Professor Alan Robock of Rutgers University with Hans Graf and Ingo Kircher of the Max Planck Institute for Meteorology performed a series of climate simulations that combined volcanic aerosol observations with upper atmosphere research satellite data from the Goddard Space Flight Center. The research team ran a general circulation model with and without Pinatubo aerosols for the two years following the Pinatubo eruption. In order to study the sensitivity of climate response to sea surface temperatures, they conducted calculations with climatology mean sea surface temperature, as well as those observed during particular El Nino and La Nina periods.

By comparing the climate simulations from the Pinatubo eruption, with and without aerosols, the researchers founds that the climate model calculated a general cooling of the global troposphere, but produced a clear winter warming pattern of surface air temperature over northern hemisphere continents. The model demonstrated that the direct radiative effect of volcanic aerosols causes general stratospheric heating and tropospheric cooling, with a tropospheric warming pattern in the winter.

“The modeled temperature change is consistent with the temperature anomalies observed after the eruption…the pattern of winter warming following the volcanic eruption is practically identical to a pattern of winter surface temperature change caused by global warming. It shows that volcanic aerosols force fundamental climate mechanisms that play an important role in the global change process”, Stenchikov added.

One of the critical conclusions from recent work is that it is important to continue the study on the impact of sizeable volcanic eruptions on the earth’s climate system in more detail, and the subsequent climate change effects.

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