Starting on March 22, a series of major eruptions have taken place from Mt. Redoubt in Alaska. The biggest exceeded 65,000 feet in height. More than a dozen eruptions as high as 60,000 have followed the first week alone. Activity may continue for weeks or months based on the volcano’s history. Climatologists may disagree on how much the recent global warming is natural or manmade but there is general agreement that volcanism constitutes a wildcard in climate, producing significant global scale cooling for at least a few years following a major eruption. However, there are some interesting seasonal and regional variations of the effects.
Oman et al (2005) and others have shown that though major volcanic eruptions seem to have their greatest cooling effect in the summer months, the location of the volcano determines whether the winters are colder or warmer over large parts of North America and Eurasia. According to their modeling, tropical region volcanoes like El Chichon and Pinatubo actually produce a warming in winter due to a tendency for a more positive North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). In the positive phase of these large scale pressure oscillations, low pressure and cold air is trapped in high latitudes and the resulting more westerly jet stream winds drives milder maritime air into the continents. Oman found high latitude volcanoes like Katmai (Alaska in 1912) instead favored the negative phase of the Arctic and North Atlantic Oscillations and cold winters. In the negative phase, the jet stream winds buckled and forced cold air south from Canada into the eastern United States and west from Siberia into Europe. They also favored a cooling of middle and higher latitudes the year round of that atmosphere and a weakening of the summer monsoon in India and Africa.
In this analysis, we looked at 11 significant high latitude volcanic eruptions in Alaska, Iceland and Russia (Kamchatka) and any observed climatic effects. Here are two examples:
The largest eruption in the world last century (VEI=6) occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 to 30 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6—about 30 to 60 times the volume erupted by Mount St. Helens in 1980! The expulsion of such a large volume of magma excavated a funnel-shaped vent 2 kilometers wide and triggered the collapse of Mount Katmai volcano. Katmai was once a cluster of 3 or 4 small volcanoes. Pyroclastic flows traveled as far as 15 miles (23 km) and filled a valley adjacent to the volcano to produce the Valley of Ten Thousand Smokes. The withdrawal of magma from beneath the cluster of small volcanoes at Katmai caused the area to collapse and produce a caldera. A lake has filled part of the caldera. The summer in the lower 48 states was a cool one nearly coast to coast.
Laki, volcano, 2,684 ft (818 m) high, S Iceland, at SW edge of the Vatnajokull glacier. Its eruption in 1783 was one of the more devastating on record, leading to the deaths of a quarter of Iceland’s inhabitants (mainly due to a famine that resulted from the eruption’s effects). Haze from the eruption spread over parts of Europe, where some experts believe it affected the inhabitants’ health.
Laki is also known for its atmospheric effects. The convective eruption column of Laki carried gases to altitudes of 15 km (10 miles). These gases formed aerosols that caused cooling in the Northern Hemisphere, possibly by as much as 1 degree C. This cooling is the largest such volcanic-induced event in historic time. In Iceland, the haze lead to the loss of most of the islands livestock (by eating fluorine contaminated grass), crop failure (by acid rain) and the death of 9,000 people, one-quarter of the human residents (by famine).
This event is rated as VEI6 on the Volcanic Explosivity Index, but the eight month emission of sulfuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium.
In Great Britain, the summer of 1783 was known as the “sand-summer” due to ash fallout. The eruption continued until 7 February 1784. Gr�msvotn volcano, from which the Laki fissure extends, was also erupting at the time from 1783 until 1785. The outpouring of gases, including an estimated 8 million tons of fluorineand estimated 120 million tons of sulfur dioxide gave rise to what has since become known as the “Laki haze” across Europe. This was the equivalent of three times the total annual European industrial output in 2006, and also equivalent to a Mount Pinatubo-1991 eruption every three days. This outpouring of sulfur dioxide during unusual weather conditions caused a thick haze to spread across western Europe, resulting in many thousands of deaths throughout 1783 and the winter of 1784.This disruption then led to a most severe winter in 1784, where an estimated to have caused 8,000 additional deaths in the UK. In the spring thaw, Germany and Central Europe then reported severe flood damage.
In North America, the winter of 1784 was the longest and one of the coldest on record. It was the longest period of below-zero temperatures in New England, the largest accumulation of snow in New Jersey, and the longest freezing over of Chesapeake Bay. There was ice skating in Charleston Harbor, a huge snowstorm hit the south, the Mississippi River froze at New Orleans, and there was ice in the Gulf of Mexico.
I averaged the 10 volcano years this last century for summer and winter temperatures. This is the summer composite finding: