Volcanoes are rarely included in simulations of future climate, because eruptions cannot be predicted. Using the behavior of past eruptions as a substitute, a new study warns that 21^st Century climate may be more variable than previously thought.

An international team led by Ingo Bethke from Uni Research and the Bjerknes Centre for Climate Research is behind a new study published in Nature Climate Change 2 October.

Figure: Global-mean temperature evolution with and without volcanic eruptions. The red curve shows how the temperature evolves from year to year in a simulation without volcanic activity. The blue curve shows the result for the simulation of the study with largest volcanic activity. Strong volcanic eruptions lead to periods of cooling that are generally followed by periods of accelerated warming. While making the climate more variable, volcanic eruptions have little influence on the long-term temperature trend. Background: NASA picture of the Sarychev eruption in 2009 on Matua Island.The study suggests that future volcanism will likely increase stresses on ecosystems and society by causing a more fluctuating climate with more extremes.

“By excluding volcanoes, existing projections of future climate miss out on how much the global climate may vary from year to year or decade to decade”, says Bethke.

Bethke and his team have used records of past volcanic eruptions obtained from ice cores to insert a range of plausible volcanic events into future climate model projections. This allows the Norwegian Earth System model to account for the various possible impacts of volcanic eruptions on future climate. The results show a potentially more variable climate than suggested by the latest assessments.    

Volcanoes cool the Earth

In Bali, 75 000 people were evacuated last week, for fears of an eruption from the volcano Mount Agung. Even a few days ahead, it is not possible to predict a volcanic eruption, but repeated tremors and gas coming out of the crater indicates that an eruption may occur soon. 

Mount Agung is one of 120 active volcanoes in Indonesia, and throughout history, eruptions in this region have affected the world’s climate. Explosive volcanic activity acts to cool the surface of the Earth, sometimes for several years and has impacts on other aspects such as rainfall. 

The devastating eruption of the volcano Tambora in Indonesia in 1815 cast a veil of aerosols over the Earth. A weather-wise extreme year followed, with frost destroying crops in Europe and North America. The year 1816 has been termed ‘the year without summer’. 

After the last eruption of Mount Agung, in 1963, the global temperature dropped between 0.1 and 0.4 degrees, according to James Hansen in Science 1978. See also the Guardian

Climate prediction without volcanoes

Currently, climate impact and risk assessments are based on climate model simulations that do not include realistic volcanic influences in the 21^st Century and hence do not cover the range of possible future outcomes.

To exclude eruptions from such simulations has been a natural choice because eruptions cannot be predicted in advance and there have been only a few such events in recent decades.

“If we are to be climate resilient, it is important to account for potential volcanic activities in our planning”, says Bethkes co-author Peter Thorne, from the Irish Climate Analysis and Research Units at Maynooth University.

Thorne stresses that such short-term volcanic cooling will not mitigate long-term human-induced climate changes.

“Even the most extreme plausible volcanic activity in the 21^st Century causes little reduction in temperatures at the end of the century.”

New ice core reconstructions

A 2,500 year-long ice core record of volcanic activity¹, sheds new light on potential future volcanism. Sulphuric acid layers in ice cores prove that several centuries were volcanically much more active than the recent one, calling into question the decision of modelling groups to omit plausible eruptions in future climate simulations.

Meanwhile, increasing computer power has enabled scientists to run larger numbers (so-called super-ensembles) of climate simulations, with each simulation representing a possible climate future. These can be used to better explore climate variability and changes in climate extremes.

Nansen Center scientist Dr. Stephen Outten is the 2nd author of the paper, that includes totally three authors from the Bjerknes Centre in Bergen.Climate prediction with volcanoes

“By analyzing the volcanic eruptions over the past 2,500 years, we were able to generate a statistically plausible volcanic activity for the 21^st Century and create sixty possible volcanic-future simulations” says co-author Stephen Outten from the Nansen Environmental and Remote Sensing Center. “Our work has demonstrated that it is not only possible to include volcanic activity in future assessments, but that it is important to do so. Preparing for future climate change without accounting for a more fluctuating climate may be a costly oversight for society.”

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¹ Sigl et al., 2015, Nature, 523, 543-549.

A discussion of the paper can be posted on Climate Lab Book by Ed Hawkins blog.

Citation and authors affiliation

Potential volcanic impacts on future climate variability

Ingo Bethke¹, Stephen Outten², Odd Helge Otter^å1, Ed Hawkins³, SebastianWagner⁴, Michael Sigl^5,6 and Peter Thorne⁷
Nature Climate Change (2017), http://dx.doi.org/10.1038/nclimate3394

1) Uni Research Climate, Bjerknes Centre for Climate Research, Bergen, Norway.

2) Nansen Environmental and Remote Sensing Center, Bjerknes Centre for

Climate Research, Bergen, Norway.

3) NCAS-Climate, Department of Meteorology, University of Reading, Reading, UK.

4) Institute for Coastal Research, Helmholtz-Zentrum Geesthacht, Germany.

5) Laboratory of Environmental Chemistry, Paul Scherrer Institute, Switzerland.

6) Oeschger Centre for Climate Change Research, University of Bern, Switzerland.

7) Irish Climate Analysis and Research Units, Department of Geography, Maynooth University, Ireland.