The world is facing into a century of extreme weather disruption as a consequence of global warming, but volcanic activity is going to be “the joker in the pack” that will test the planet’s coping abilities, a new study has predicted.
Volcanoes are rarely included in simulations of future climate, because eruptions cannot be predicted. But following an evaluation of the behaviour of past eruptions as a substitute, researchers at the University of Bergen and Maynooth University warn that 21st century climate may be more variable than previously thought.
The study led by Dr Ingo Bethke of the Bjerknes Centre for Climate Research and Prof Peter Thorne of Irish Climate Analysis and Research Units in Maynooth, suggests "future volcanism will likely increase stresses on ecosystems and society by causing a more fluctuating climate with more extremes."
Volcanoes have a severe and rapid cooling effect, which can extend over much of the planet. This is usually followed quickly by a period of warming. “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. The results show a potentially more variable climate than suggested by the latest assessments” Dr Bethke said.
The research team, whose study is published in Nature Climate, used records of past volcanic eruptions obtained from ice cores to insert a range of plausible volcanic events into future climate model projections. This allowed the “Norwegian Earth System model” to account for the various possible impacts of volcanic eruptions on future climate..
The world has not seen a major volcanic event for at least 25 years, but the tropical volcano Mt Agung on Bali is now threatening to erupt. Some 75 000 people were evacuated from its vicinity last week. 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. It 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 year of extreme weather 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.
Climate impact and risk assessments were previously based on climate model simulations that did not include realistic volcanic influences in the 21st Century and hence did not cover the range of possible future outcomes, explained Prof Thorne. To exclude eruptions from such simulations has been a natural choice because eruptions cannot be predicted in advance and there have been so few of such events in recent decades.
A 2,500 year-long ice core record of volcanic activity shed 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.
Increased computer power enabled the scientists run larger numbers (so-called super-ensembles) of climate simulations. These can be used to better explore climate variability and changes in climate extremes. Combining knowledge about past volcanism with running 60 possible volcanic-future simulations, Bethke and Thorne demonstrate that including plausible volcanic activity is possible and important in future assessments. “If we are to be climate resilient, it is important to account for potential volcanic activities in our planning,” Prof Thorne added.
Such short-term volcanic cooling will not mitigate long-term human-induced climate changes, he stressed. “Even the most extreme plausible volcanic activity in the 21st century causes little reduction in temperatures at the end of the century.”
