Volcanic eruptions can cool the planet

Indonesian authorities ordered an evacutation of the area around Bali's Mount Agung volcano as it erupted Sunday. Other volcanic eruptions have cooled the climate, with one even leading to the "year without a summer."

Plunging temperatures, snow, freezing rain and gloomy days devoid of sunshine - such was the weather scenario in 1816. So cold and miserable that it became known as the year without a summer.

From China to Europe and North America, crops failed, famine-like conditions prevailed, and infectious diseases spread, leaving a trail of civil unrest in their wake. As devastating as the inclement weather and its consequences were, they inspired their share of dark literary masterpieces.

It was during that year that Mary Godwin penned her stormy and bleak Frankenstein, while her soon-to-be husband, poet Percy Shelley, wrote of the extinguished sun and stars and the mornings that "came and went and came, and brought no day."

Indonesien Vulkan Tambora auf Sumbawa

Mount Tambora on quieter days

At the time, the reason for the summer's disappearance was unknown, and it wasn't in fact until the 20th Century that scientists began to link it to the four-month eruption of Indonesia's Mount Tambora in April 1815.

Read more: Why an eruption of Bali's Mount Agung is so dangerous

A huge explosion with global consequences

It was one of the largest volcanic eruptions on record, which a book entitled The Year Without Summer, says claimed more than 70,000 lives. According to the UCAR Center for Science Education, it also spewed such vast amounts of ash into the atmosphere that the sun was blocked from view and houses in nearby towns collapsed beneath thelarge particles that coated them. 

The eruption was so powerful that smaller particles of ash and sulphate aerosols (SO2) spread into the stratosphere and distributed around the world, affecting the global climate.

Leuchtende Lavaströme Tungurahua Vulkan

It is hard to equate such violent heat with a cooling effect

Volcanic ash shades sunlight and causes temporary cooling, but aerosols reflect incoming solar radiation and can stay in the stratosphere for longer periods. The earth's average temperature temporarily dropped by 3 degrees Celsius.

Cooling volcanoes

The Mount Agung eruption is not expected to be big, according to the Indonesian authorities. Indeed, Tambora-scale eruptions have been relatively rare in human history. The Indonesian volcano had been dormant for more than 1,000 years. But smaller blasts can also affect global climate and temperature.

Read more: Bali's Mount Agung volcano erupts, prompting mass evacuation order

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When Mount Pinatubo in the Philippines blew in 1991, it pumped 17 million tons of SO2 into the atmosphere and caused an approximate 0.6 degrees Celsius cooling effect in the Northern Hemisphere in 1992 and 1993, writes Scientific American.

Researchers and policymakers have been looking at ways to use this explosive cooling effect to help reverse global warming. Ideas include continuously spraying sulphate aerosols into the stratosphere to reflect sunlight. But there are currently too many uncertainties regarding the consequences of such "climate engineering" to take action.


Mount Agung

Villagers gather outside the 12-kilometer (7.5-mile) exclusion zone in the Karangasem Regency in Northeast Bali to get a look at Mount Agung. People located outside the exclusion zone have also evacuated, fearing an eruption of the volcano is imminent.


Praying for hope

Last week, Balinese residents carried offerings to pray at a temple on the resort island. Indonesian officials raised the alert level of the volcano to its highest level, which means an eruption is imminent.


Abandoned island

Tulamben, a village on Bali famous for its scuba diving, appeared completely deserted on Thursday as the mass exodus continued. Indonesian officials said more than 120,000 people have evacuated the region around Mount Agung.


Taking shelter

Evacuees have gathered in camps like this one in Klungkung in southeast Bali as they heed warnings that the volcano will erupt. Over 500 locations on the resort island, including sporting centers and public buildings, have been turned into shelter evacuees.


Learning from history

On Wednesday, Indonesian President Joko Widodo visited one of the camps in Klungkung. Mount Agung last erupted in 1963, killing 1,100 people as it spewed ash clouds, toxic gases and rock fragments that traveled down the mountain at high speeds.


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