Scientists recognize that there are many factors that control our climate. Volcanic eruptions are one factors. Although we have known this for a long time, how the volcanic-climatic process works is still not fully understood.
In late 1700s, Ben Franklin recognized that abnormally cold summer of 1783 in the northern hemisphere was related to the large scale basaltic eruption of the Laki fissure in Iceland. This volcanic event produced an ash cloud reaching into the upper stratosphere and dense haze from Europe to Siberia that dimmed the sun. It also lowered temperatures in the northern hemisphere by 1 C.
Initially, scientists believed that it was volcanic ash clouds that had the dominant effect on global temperatures. However, it was only in 1982, after eruption of El Chichn in Mexico, did this view change. Just two years earlier, the massive eruption of Mt. St. Helens in Washington had lowered global temperatures by about 0.1 degree C. The much smaller eruption of El Chichn, had three to five times the global cooling effect worldwide. The difference was El Chichn emitted more than 40 times the volume of sulfur-rich gases than Mt. St. Helens.
Of the two main types of volcanic eruptions, rhyolitic and basaltic, it is basaltic eruptions that release large amounts of sulfur into the atmosphere, mostly as SO2 and H2S, and can have extreme climatic and environment consequences.
Scientist have now linked flood basalt eruptions with major fauna and flora extinction events in the last 500 million years. There have been as many as 11 basaltic eruptions associated with various extinction events and five basaltic eruptions associated with major extinctions.
The largest of these basaltic eruptions occurred around 251 million years ago, at the boundary of Permian-Triassic geological periods. At this time, the massive eruption of the basaltic Siberian Traps in Russia produced the world’s largest extinction, killing almost all life on the planet. This mass extinction has also been referred to as ‘the Great Dying’.
During this eruption, basaltic lava flooded an area about 7 million square kilometers with up to 4 million cubic kilometers of basaltic magma. The series of eruptions lasted 1 million years and was responsible for the extinction of 96% of ALL marine species, 70% of all terrestrial vertebrate species and ALL insects becoming extinct.
It was a devastating effect. Large expanses of land were scorched with acid rain, the atmosphere became clouded with dust, climate-altering greenhouse gases were released into the atmosphere causing global warming and caused acidification. The temperature rose by 8C, CO2 level increased to 2000 ppm.
Extreme environmental conditions persisted for around 5-10 million years after the eruptions stopped.
It was only after the environmental volatility subsided did more complex ecosystem emerged. New groups such as crab and lobsters, as well as reptiles, appeared. Despite all the negative consequences of the eruptions, the event had re-set evolution and new advanced life emerged. It was the catalyst of early modern life.
And now, researchers at Harvard believe larger volcanic eruptions occur in regular cycles. S Kutterol, et. al. (2013) have dated volcanic ash in Pleistocene rock along the Pacific ‘Ring of Fire’ and conclude large eruption have occurred in 40,000 and 100,000 year cycles. They believe these volcanic cycles also correspond to Milankovitch Cycles (Climate Change- A Geological Perspective), or the regular changes in the Earth’s elliptical orbit and also the axis of the earth rotation. They reasoned that change in orbital and rotational axis cause changes the areas of weakness in stress regime at the earth’s surface where eruptions occur.
There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more volcanoes which are under our oceans. Underwater volcanoes effect the temperature of the ocean, which also effects the amount of CO2 and water vapor in the atmosphere. Both components lead to increased climatic warming. And oceans are the primary source of atmospheric CO2. Therefore, ocean temperature has a very important climatic effect.
We now know volcanism, the global carbon cycle and climate are certainly connected. However, our earth’s climate is a complex process that is a result of the interplay between many factors that are not fully understood. Volcanic activity is just one factor.
Solar output, interstellar dust, Milankovitch Cycles, plate tectonics, oceanic temperature, atmospheric chemistry and not least, volcanic activity ALL effect earth’s climate.
There is a famous weather forecaster, Ms. Evelyn Browning Garriss, who became known as the ‘Volcano Lady’ because of the high frequency of volcanic activity that affected her seasonal weather predictions. We have uploaded a video of her discussing volcanic influence on weather.
I believe our ability to predict our future climate is limited by the understanding of the interplay between ALL the climatic factors. We need far more research and more refined climatic modelling to develop meaningful climatic models. Until this happens it is hard to differentiate between man’s footprint and natural factors.