Earlier this year geologists warned that North Korea's nuclear tests could trigger an eruption of the Mount Paektu volcano. New research shows just how much of a worry that is, with evidence that Paektu's last big eruption released far more sulfur than previously thought.

Paektu sits on the border between China and North Korea, making it one of the most difficult places on Earth for scientists to study. Nevertheless, it is known that a little over a thousand years ago the mountain underwent a major eruption. Research published in Science Advances suggests this released more sulfur than the fearsome explosions from Krakatau and Tambora.

Paektu's most recent eruption is thought to have occurred in 946 CE. We don't have records of the event, but an estimated 23 cubic kilometers (5.5 cubic miles) of rock was hurled into the air, along with enormous amounts of carbon dioxide and sulfur. The effects of these on the climate would have been contradictory, with the CO₂ warming the world while the sulfur particles reflected sunlight and cooled us down.

The timescales of these two contributions would have been different. Sulfur washes out of the air relatively quickly, causing one or two cool years, while we are learning – to our sorrow – how long carbon dioxide sticks around.

A team led by Dr Kayla Iacovino of the US Geological Survey set out to quantify how much sulfur Paektu injected into the atmosphere. Past estimates have used what is known as the petrologic method comparing concentrations of volatile materials in the first crystals formed in the eruption and those left behind in later material. However, satellite observations of recent eruptions have found that this often underestimates how much sulfur is released.

Iacovino adopted a different method, examining the way certain crystals form and their distribution in the magma the explosion left behind. These figures were combined with estimates of the way gases were released to produce a total sulfur estimate, which exceeds that of the Mount Tambora explosion of 1815.

The paper then looks at what impact this is likely to have had on the climate of the era. The Tambora eruption led to what is known as the “Year Without A Summer” in 1816 after dust and sulfur blocked so much sunlight temperatures stagnated and crops withered.

The effects of Paektu's eruption were much less dramatic, which the authors attribute to Paektu being at a higher latitude. An eruption coinciding with winter, when stratospheric particles are removed more quickly from polar regions, would have helped as well.

Evidence that Paektu is building towards a future eruption has grown so strong that the notoriously uncooperative North Korean government has sought help from international scientists to assess the risks. Such an explosion would not necessarily replicate the 946 event in size, but if it did, the impact could be found far beyond the Korean peninsula.

^{The sulfur from the Mt Tambora explosion caused a worldwide cooling and starvation from crop failure. Mt Paektu released even more (Note that since the scale is logarithmic the difference is later than it looks.) Carla Schaeffer/AAAS}