Volcanic eruptions could lead to “years without summers” – and climate change is to blame

If the climate continues to change at its current rate, our children – and even some of us – could experience “years without summers” in the not too distant future.

By studying the potential impact major volcanic eruptions could have on Earth in the future, scientists have warned that our oceans will no longer be capable of buffering the effects any erupting sulphur and aerosols will have on our atmosphere as they have done in the past.

The research was led by the National Center for Atmospheric Research (NCAR) in the US. Its authors began by studying the impact the eruption of Indonesia’s Mount Tambora had on Earth’s climate in April 1815. It is believed – and this study appears to have confirmed – that this devastating eruption triggered the so-called “year without a summer” in 1816.

According to data from the Community Earth System Model’s (CESM) Last Millennium Ensemble Project, which simulates Earth’s climate using the historical record of volcanic eruptions from the year 850 to 2005, the eruption caused a significant global cooling event. 

In particular, Mount Tambora’s eruption in April 1815 threw sulfur dioxide into Earth’s upper atmosphere where it became sulfate particles called aerosols. This thin layer of particles reflected light from the Sun away from Earth which cooled the planet and subsequently caused more snow and ice to form over larger areas of land, particularly in Europe.

This is said to have caused temperatures the following summer, in 1816, to plummet which in turn have been linked to widespread crop failure, disease and the deaths of 100,000 people.

Researchers then ran CESM’s historical data forward and simulated a Mount Tambora-style eruption in 2085 – assuming greenhouse gas emissions continue to rise as they are.

The historical simulations revealed that two climatic processes helped regulate Earth’s temperature after Mount Tambora’s eruption. As the aerosols fuelled a rise of snow and ice on land, and reflected heat from the planet, the surface of the oceans cooled in line with the increasing ice, causing colder water to sink and warmer water to rise and release heat back into the atmosphere.

As the aerosol layer dissipated, more heat reached Earth, at which point the ocean helped cool the atmosphere as large bodies of water take longer to warm up and release heat than land.

If a similar eruption was to take place in 2085, the simulations show that global temperatures would plunge “more deeply” than in 1815. Rather than increase the amount of land covered by snow and ice, though, the future warming predicted by climate change would see coverage remain approximately the same.

This sounds like relatively good news, however, in the future models the ocean is more stratified. As our climate warms, sea surface temperatures rise and the warmer water at the ocean’s surface is less able to mix with the colder, denser water below.

In the simulations, this increase in ocean stratification could cause the water that is cooled following the volcanic eruption to become trapped at the surface instead of mixing deeper into the ocean, reducing the amount of heat released into the atmosphere.

This means the ocean’s ability to moderate the cooling of the land in 2085 would be diminished “substantially”. These cooler sea surface temperatures would also decrease the amount of water that evaporates into the atmosphere and, therefore, reduce global average rainfall and precipitation. This could play further havoc on crops.

What’s more, the cooling of the Earth (modelled at around 1.1 degrees Celsius) would not be enough to offset the warming caused by climate change, predicted to reach 4.2 degrees Celsius by 2085.

The findings are presented with a word of caution, however. The exact effects and magnitude of the cooling is “difficult to quantify,” according to the researchers, since there were only a small number of simulations to work with.

It is also not known how the climate will respond between now and the time of a major eruption, and how it will react to changes and policies being introduced by governments.

“The response of the climate system to the 1815 eruption of Indonesia’s Mount Tambora gives us a perspective on potential surprises for the future, but with the twist that our climate system may respond much differently,” author Otto-Bliesner explained.

The research is published in the journal Nature Communications.