200 Years Ago This Week: Tambora's Eruption Causes a Planet-Wide Climate Emergency

Two hundred years ago this week, an obscure volcano in Indonesia named Tambora rumbled to life after centuries of dormancy. On April 5, 1815, huge plumes of fire jetted from the mountain for three hours, rocking the ground and painfully assaulting the ears of the local residents. But the eruption suddenly stopped, and the great mountain lapsed back into a fitful slumber. During the week that followed, Tambora sent occasional plumes of ash into the air, but most of the residents that had fled the initial eruption returned to farm the fertile soils on the flanks of the volcano. But on April 10, 1815, the mightiest volcanic explosion ever witnessed and recorded by humans rent Tambora in a cataclysmic eruption heard more than 1,200 miles (2,000 km) away. As recounted in Gillen D'Arcy Wood's excellent 2014 book, Tambora: The Eruption That Changed the World, "three distant columns of fire burst in cacophonous roar from the summit to the west, blanketing the stars and uniting in a ball of swirling flame. The mountain itself began to glow as stream of boiling liquified rock coursed down its slopes." Whole villages, totaling perhaps 10,000 people, were consumed by fiery pyroclastic flows. Tambora threw so much rock into the air that the mountain collapsed in on itself, chopping 9/10 of a mile (1.5 km) off the height of the mountain, and creating a massive caldera 4 miles (7 km) wide. The volcano's ash cloud covered an area nearly twice the size of the continental U.S., and at least 60,000 people died from the combined effect of Tambora's ash, pyroclastic flows, and tsunamis.


Figure 1. Aerial view of the caldera of Indonesia's Mount Tambora, formed during the colossal 1815 eruption. Image credit: Wikipedia.

Tambora creates a climate emergency
Tabora's eruption was a magnitude 7 event on the Volcanic Explosivity Index (VEI)--a "super colossal" eruption that one can expect to occur only once every 1000 years. The Volcanic Explosivity Index is a logarithmic scale like the Richter scale used to rate earthquakes, so a magnitude 7 eruption would eject ten times more material than the two largest eruptions of the past century--the magnitude 6 eruptions of Mt. Pinatubo in the Philippines (1991) and Novarupta in Alaska (1912).

The Tambora eruption threw so much sulfur dioxide (SO2) gas into the stratosphere that a "Volcanic Winter" resulted. Sulfur dioxide reacts with water to form sulfuric acid droplets (aerosol particles), which are highly reflective and reduce the amount of incoming sunlight. The sulfur pumped by this eruption into the stratosphere dimmed sunlight so extensively that global temperatures fell by about 0.4–0.7 °C (0.7–1.3 °F) for 1 - 2 years afterward, triggering the infamous Year Without a Summer in 1816. In Western Europe, summer temperatures in 1816 were up to 3°C (5.4°F) below average, resulting in crop yields that plunged more than 75%. Tens of thousands died of starvation, and tens of thousands more died in the typhus epidemic that followed. The situation was even more dire in India, where the eruption caused the failure of the monsoon rains from June through August 1816--the longest recorded break in the Southwest Monsoon in recorded history. The resulting famine and cholera epidemic that erupted ended up killing millions over the next few decades. Unprecedented July snows also hit Yunnan, China in 1816, resulting in widespread famine, and killing frosts in June, July, and August 1816 in Eastern Canada and New England caused widespread crop failures. A cold wave on June 5 - 11 dumped up to a foot of snow on the Northeast U.S., and lake and river ice were observed as far south as Pennsylvania in July and August.


Figure 2. Summertime temperatures in Europe during the summer of 1816 were up to 3°C (5.4°F) below average over France, Switzerland, and Spain. Image credit: Giorgiogp2 on Wikipedia Commons.


Figure 3. A promotional photo of Boris Karloff as Frankenstein's monster, using Jack Pierce's makeup design. The failure of the Southwest Monsoon in 1816 due to the ash cloud from Tambora caused storm tracks over Western Europe to shift to the south, and recurrent low pressure systems brought cold air and heavy and long-lasting rainfall to western and central Europe. While trapped indoors for weeks by constant rain and gloomy skies during her vacation at Lake Geneva in Switzerland during the summer of 1816, Mary Shelley was inspired to write Frankenstein, a horror novel set in an often stormy environment. Image credit: Wikipedia.

Magnitude 7 Super-colossal eruptions
In an article published in 2008 in the American Geophysical Union journal EOS, Dr. Ken Verosub of the University of California, Davis Department of Geology estimated that future eruptions capable of causing "Volcanic Winter" effects severe enough to depress global temperatures by 2°F (1°C) and trigger widespread crop failures for 1 - 2 years afterwards should occur about once every 200 - 300 years. Even a magnitude 6 eruption, such as the 1600 eruption of the Peruvian volcano Huaynaputina, can cause climatic change capable of killing millions of people. The Huaynaputina eruption is blamed for the Russian famine of 1601-1603, which killed over half a million people and led to the overthrow of Tsar Boris Godunov. Thankfully, the climatic impacts of all of these historic magnitude 6 and 7 eruptions have been relatively short-lived. After about two years, the sulfuric acid aerosol particles have settled out of the stratosphere, returning the climate to its former state.

Magnitude 8 Mega-colossal eruptions
Even more extreme eruptions have occurred in Earth's past--eruptions ten times more powerful than the Tambora eruption, earning a ranking of 8 out of 8 on the Volcanic Explosivity Index (VEI). These "mega-colossal" eruptions occur only about once every 10,000 years, but have much longer-lasting climatic effects and thus are a more significant threat to human civilization. A mega-colossal eruption at Toba Caldera, Sumatra (Indonesia), about 74,000 years ago, was 3500 times greater than the Tambora eruption. According to model simulations, an eruption this large can pump so much sulfur dioxide gas into the stratosphere that the atmosphere does not have the capacity to oxidize all the SO2 to sulfuric acid aerosol. The atmosphere oxidizes as much SO2 as it can, leaving a huge reservoir of SO2 in the stratosphere. This SO2 gradually reacts to form sulfuric acid as the OH radicals needed for this reaction are gradually produced. The result is a much longer-lasting climate effect than the 1 - 2 years that the magnitude 6 and 7 events of Tambora of 1815 and Pinatubo of 1991 lasted. A magnitude 8 eruption like the Toba event can cool the globe for 6 - 10 years by 3 - 5°C (5 - 9°F), and the controversial Toba Catastrophe Theory asserts that the resulting sudden climate change reduced the Earth's population of humans to 1,000 - 10,000 breeding pairs, creating a "genetic bottleneck".


Figure 4. The 100x30 square kilometer Toba Caldera is situated in north-central Sumatra around 200 km north of the Equator. It is comprised of four overlapping calderas aligned with the Sumatran volcanic chain. Repeated volcanic cataclysms culminated in the stupendous expulsion of the Younger Toba Tuff around 74,000 years ago. The lake area is 100 square kilometers. Samosir Island formed as a result of subsequent uplift above the evacuated magma reservoir. Such resurgent domes are typically seen as the concluding phase of a large eruption. Landsat Enhanced Thematic Mapper Plus (ETM+) browse images for path/row 128/58 (6 September 1999) and 129/58 (21 January 2001) from http://landsat7.usgs.gov/. Copyright USGS. Image source: Oppenheimer, C., 2002, "Limited global change due to the largest known Quaternary eruption, Toba 74 kyr BP?"Quaternary Science Reviews, 21, Issues 14-15, August 2002, Pages 1593-1609.

When can we expect the next magnitude 8 eruption?
Given the observed frequency of one mega-colossal magnitude 8 volcanic eruption every 1.4 million years, the odds of another hitting in the next 100 years is about .014%, according to Mason et al., 2004. This works out to a 1% chance over the next 7200 years. Rampino (2002) puts the average frequency of such eruptions at once every 50,000 years--about double the frequency with which 1-km diameter comets or asteroids capable of causing a similar climatic effect hit the Earth. A likely location for the next mega-colossal eruption would be at the Yellowstone Caldera in Wyoming, which has had magnitude 7 or 8 eruptions as often as every 650,000 years. The last mega-colossal eruption there was about 640,000 years ago. But don't worry, the USGS states that "the Yellowstone volcanic system shows no signs that it is headed toward such an eruption. The probability of a large caldera-forming eruption within the next few thousand years is exceedingly low".

What would happen if a magnitude 8 mega-colossal eruption were to occur today?
If a mega-colossal eruption were to occur today, it would probably not be able to push Earth into an ice age, according to a modeling study done by Jones et al. (2005). They found that an eruption like Toba would cool the Earth by about 17°F (9.4°C) after the first year (Figure 5), and the temperature would gradually recover to 3°F (1.8°C) below normal ten years after the eruption. They found that the eruption would reduce rainfall by 50% globally for the first two years, and up to 90% over the Amazon, Southeast Asia, and central Africa. This would obviously be very bad for human civilization, with the cold and lack of sunshine causing widespread crop failures and starvation of millions of people. Furthermore, the eruption would lead to a partial loss of Earth's protective ozone layer, allowing highly damaging levels of ultraviolet light to penetrate to the surface.

Not even a mega-colossal eruption of this magnitude would stop global warming, though. The level of greenhouse gases in the atmosphere would not be affected by the volcanic eruption, and warming would resume where it left off once the stratospheric dust settled out in a decade. With civilization crippled by the disaster, greenhouse gas emissions would be substantially reduced, though (small solace!) If we really want to say goodbye to civilization, a repeat of the only magnitude 9 eruption in recorded history should do the trick--the magnitude 9.2 La Garita, Colorado blast of 27.8 million years ago (Mason et al., 2004).


Figure 5. Annual near-surface temperature anomalies for the year following a mega-colossal volcanic eruption like the Toba eruption of 74,000 years ago, if it were to occur today. Most land areas cool by 22°F (12°C) compared to average. Some areas, like Africa, cool by 29°F (16°C). Image credit: Jones, G.S., et al., 2005, "An AOGCM simulation of the climate response to a volcanic super-eruption", Climate Dynamics, 25, Numbers 7-8, pp 725-738, December, 2005.

What would happen if a magnitude 7 super-colossal eruption were to occur today?
An eruption today like the magnitude 7 Tambora eruption of 1815 would cause cause isolated regional crop failures for 1 - 2 years after the eruption. With food supplies in the world already stretched thin by rising population, decreased water availability, and conversion of cropland to grow biofuels, such a volcanic eruption might trigger regional famine, threatening the lives of millions of people and potentially igniting wars over scarce resources. However, society's vulnerability to major volcanic eruptions is less than it was, since the globe has warmed significantly in the past 200 years. The famines from the eruptions of 1600 and 1815 both occurred during the Little Ice Age, when global temperatures were about 1.4°F (0.8°C) cooler than today. Crop failures would not be as wide-spread with today's global temperatures, if a super-colossal eruption were to occur. Fifty years from now, when global temperatures are expected to be at least 1.8°F (1°C) warmer, a magnitude 7 eruption should only be able to cool the climate down to year 2009 levels.

For further information
Tambora: The Eruption That Changed the World, a 2014 book by Gillen D'Arcy Wood, is an excellent read.

Volcanic Winter, my April 2009 post.

Volcanic winter article from wikipedia.

Realclimate.org has a nice article that goes into the volcano-climate connection in greater detail.

The International Conference on Volcanoes, Climate, and Society is holding a special conference this week in Switzerland, Bicentenary of the great Tambora eruption (thanks go to Mike Chenoweth for alerting me to this.)

References
Jones, G.S., et al., 2005, "An AOGCM simulation of the climate response to a volcanic super-eruption", Climate Dynamics, 25, Numbers 7-8, pp 725-738, December, 2005.

Mason, B.G., D.M. Pyle, and C. Oppenheimer, 2004, "The size and frequency of the largest observed explosive eruptions on Earth", Bulletin of Volcanology" 66, Number 8, December 2004, pp 735-748.

Verosub, K.L., and J. Lippman, 2008, "Global Impacts of the 1600 Eruption of Peru's Huaynaputina Volcano", EOS 89, 15, 8 April 2008, pp 141-142.

Jeff Masters