Little Ice Age volcanism refers to the massive volcanic activities during the Little Ice Age. Scientists suggested a hypothesis that volcanism was the major driving force of the global cooling among the other natural factors, i.e. the sunspot activities by orbital forcing and greenhouse gas. The Past Global Change (PAGES), a registered paleo-science association for scientific research and networking on past global changes in the University of Bern, Switzerland, suggested that from 1630 to 1850, a total of 16 major eruptions and cooling events had taken place. When a volcano erupts, ashes burst out of the vent together with magma and forms a cloud in the atmosphere. The ashes act as an isolating layer that block out a proportion of solar radiation, causing global cooling. The global cooling effect impacts ocean currents, atmospheric circulation and cause social impacts such as drought and famine. Wars and rebellions were therefore triggered worldwide in the Little Ice Age. It was suggested that the crisis on Ottoman Empire and Ming-Qing Transition in China were typical examples that closely correlated with Little Ice Age.
Volcanism during the Little Ice Age
Three major cooling periods
Three large cooling periods caused by volcanic eruptions in 1641–1642, 1667–1694 and 1809–1831 respectively. Also, some major volcanic eruptions caused the fall of the temperature. During the Little Ice Age, all major volcanic eruptions were stratovolcano, also known as composite volcanos. They were built by the escape of magma through separate vents over thousands of years, accumulated into layers. A large amount of sulfate and volcanic ashes escaped from the volcano, resulting in a significant decrease in temperature.
1641–1642
Komaga-take volcano, Japan (1640) (probably the largest eruption in Japan's history, deposited a large amount of ashes) Mount Villarica, Chile (1640) Parker Volcano, Philippines (1641)
1667–1694
Shikotsu (Tarumae), Japan (1667) Gamkonora , Halmahera (1673) Tongkoko , Sulawesi (1680)
1809–1831
Tambora, Indonesia (1815) (The largest eruption known in history) Galunggung, Indonesia (1822) *Two unknown volcanic activities (1809, 1831) Cosigüina Volcano, Nicaragua (1835)
Other major volcanic eruptions
Long Island, New Guinea (1660) Usu, Japan (1663) Mount Fuji, Japan (1707) Shikotsu (Tarumae), Japan (1739) St Helens, Washington, US (1800)
*All Volcanic Eruptions have a Volcanic Explosivity Index (VEI) of 5 or above. It means that the volume of gases and aerosols ejected were more than 1 km3 and the eruption column height was more than 25 km.
Cooling effect of volcanic eruptions
Volcanoes are usually formed along plate boundaries or hotspots. Each eruption allows lava, volcanic ash and gases (toxic gases and greenhouse gases) to escape from the magma chamber under the surface. The escaped materials trigger the global cooling effect.
Global cooling
The temperature on the surface is affected by the greenhouse effect. During the Little Ice Age, volcanic eruptions produced ashes that blocked solar insolation. The Earth surface received less radiation, the temperature decreased significantly. The effect lasted for around 6–8 years (Fig. 5). In addition, sulfur dioxide produced from eruptions reacted with the ozone layer to form sulfuric acid. Fine sulfate aerosols were formed in the atmosphere, which increased the reflection of solar and caused global cooling.
Correlation between volcanism and Little Ice Age
Scientists pointed out several natural causes of the Little Ice Age, e.g. volcanic activity, orbital cycles, decreased solar activity and Greenhouse gas. Gabriele C. Hegerl compared the different forcing of Little Ice Age based on various studies. An energy balance model was simulated, with volcanic, solar and greenhouse gas signals as parameters. They created various models to calculate the correlation between natural forcing and temperature change. It showed natural forcing acted as an important role in temperature change (Fig. 5). Also, the research also compared the contribution of temperature change among three natural factors. Volcanic activities was the main driver of the Little Ice Age (Fig. 7), because volcanism was the largest forcing.
Geophysical impact
Little Ice Age Volcanism caused a temperature anomaly. It affected the climate system, i.e. the atmosphere, the hydrosphere. The influence of the climate system would cause the impact of the ecosystem and the society.