Environmental Impact of the Eyjafjallajökull Eruption
Most news stories surrounding the Icelandic volcano eruption focus on the effect of the ash cloud on air transportation in Europe and the world economy. While this is an interesting and important consideration, over here at Tiny Science I am more interested in the impact of this eruption on Earth’s climate.
Lava and ash are the most obvious products of a volcanic eruption, but eruptions produce and release lots of chemicals and gases that we don’t see. Among those gases are sulfur dioxide (SO2) and carbon dioxide (CO2) both of which have the potential to change the Earth’s climate.
Sulfur dioxide from volcanoes could lead to short-term global cooling
According to NASA (yes Virginia, NASA does climate research) sulfur dioxide (SO2) produced by volcanic eruptions could be a major player in ozone depletion and short-term climate change. Sulfur dioxide mixes with water in the atmosphere to produce fine particles (aerosols) of sulfuric acid (H2SO4). This sulfuric acid can combine with atmospheric chlorine molecules from chlorofluorocarbons (CFCs) and produce compounds that react with ozone (O3) and deplete it from the upper atmosphere, causing a decrease in the protection ozone gives us from ultraviolet (UV) rays.
If enough sulfuric acid aerosol is produced in the upper part of the atmosphere known as the stratosphere, it can also reflect back a significant amount of solar energy, keeping it from reaching the Earth’s surface and warming the planet. This radiative transfer can cause short-term global cooling, effecting global climate for a year or two after the eruption.
It is important to note that actual evidence supporting this hypothesis is limited. There are not many large-scale volcanic eruptions on Earth, which is good for people living near volcanoes, but means there are few opportunities for scientists to gather data on how much sulfur dioxide is produced during an eruption, where it ends up in the atmosphere, and what other gases produced by the eruption could be affecting climate in the short and long term. Global climate modeling is also extremely complicated. There are dozens of factors which work to warm and cool the Earth, and scientists are still working to understand how they all work together to produce the climate patterns that we see. So figuring out how a specific eruption fits into short-term climate change is challenging and inexact.
Current observations indicate that major volcanic eruptions are often followed by a year or more of cooler than average global temperatures.
For example, the massive 1815 eruption of the Tambora volcano (on the island of Sumbawa, Indonesia) was followed by the “Year Without a Summer” in which most of Europe, the Northeastern United States and Eastern Canada experienced killing frosts and snow well into the summer of 1816. Astronomers will point out that other factors could have contributed to that year’s extreme temperatures along with the volcano (remember, climate is a complex thing).
The devastating 1963-64 eruption of Bali’s Gunung Agung is credited with lowering global temperatures in the mid-1960’s. The colossal (really, that’s what it’s officially classed as, colossal) June 1991 eruption* of Mt. Pinatubo in the Philippines ejected 15-30 million tons of sulfur dioxide into the atmosphere. According to the US Geological Survey, this sulfur aerosol cooled global temperatures by as much as 0.5 C through 1993. The United States experienced the third coldest and wettest summer of the 20th century in 1992, with the heavier than usual rain and snowfall leading to large-scale flooding across much of the United States in 1992 and 1993, most notably along the Mississippi and Missouri river basins.
It is important to note, however, that not all large volcanic eruptions are followed by short-term global cooling. The large 1982 El Chichon eruption in Mexico was not followed by cooler than normal global temperatures. NASA points to the strong warming effect of that year’s El Nino in the Pacific as one possible explanation, suggesting that the El Nino effect canceled out the cooling effect of the eruption.
As climate models get more sophisticated and make more accurate predictions, it will be easier to determine the effects volcanic eruptions will have on global climate.
Compared with the eruptions discussed above, the Eyjafjallajökull eruption is rather small. The Eyjafjallajökull volcano’s ash plume pulsed to 5 miles (8 km) high at some points during the eruption. This is probably not high enough to eject a significant amount of material into the stratosphere. Professor Brian Toon, chair of the Atmospheric and Oceanic Sciences Department at the University of Colorado and an expert on atmospheric aerosols and their effects on climate has predicted that an eruption of this size is unlikely to cause significant global climate change.
* Mt. Pinatubo’s ash plume was 21 miles (34 km) high and over 250 miles (400 km) wide during the most active part of its eruption. This eruption was the second largest of the 20th century, ten times larger than Mt. St. Helens.
A short note on human vs. volcanic CO2 production and the Eyjafjallajökull eruption
Volcanic eruptions also produce carbon dioxide (CO2), another potent greenhouse gas. Increased CO2 in the atmosphere is associated with an increase in global temperature. But is a volcanic eruption a significant source of CO2? And how could the CO2 from the Eyjafjallajökull eruption impact global climate?
The Information is Beautiful blog has produced a striking graphic (this is their corrected version) showing that the CO2 production of the Eyjafjallajökull eruption is significantly smaller than the amount of CO2 produced by the European aviation industry (compared in units of tons per day). Considering the eruption canceled 60% of flights in Europe for several days, the end effect is that the eruption actually offset its own CO2 production and then some, saving a net 50,000 tons of CO2 from entering the atmosphere by grounding flights. Links to the primary data for the graphic are on the Info. is Beautiful website.