Findings: Volcano threat to climate

The possibility of asteroids or comets hitting Earth is considered a real threat, and investigation into their detection, deflection or destruction is high on most science agendas, writes Caroline Davis. But an American scientist believes we face an even greater threat from the Earth itself - in the form of volcanic super-eruptions.

Michael Rampino, an expert in earth and environmental science at New York University, said: "As much thought needs to be given to volcanoes as to asteroid impacts. They can be just as disastrous, and it is hard to think what one can do for prevention. They have more impact and happen more often."

Large volcanic eruptions can produce more than 1,000km3 of lava and enormous atmospheric clouds of dust and suspended matter. The clouds reflect solar radiation, leading to climatic cooling that could threaten crops, causing famine, conflict and ecological disaster.

Dr Rampino estimates that such super-eruptions happen about every 50,000 years, twice as often as asteroid impacts that would have similar effects.

Dr Rampino said the last super-eruption - at Mount Toba, Sumatra, about 73,000 years ago - created clouds that lasted six years, cooling the Earth by up to 5C and reducing the human population to a few thousand.

Toba's effect was calculated to be similar to that of the impact of an asteroid 1km across, which would cause global climate catastrophe and destruction of the ozone layer.

The most recent major eruption was in 1815 in Tambora, Indonesia. It has been associated with a 1C drop in temperatures in the northern hemisphere. This made 1816 cold and wet - the "year without a summer" - and led to crop failure and famine.

Although progress has been made on short-term eruption prediction, Dr Rampino said: "No method has proven successful in consistently predicting the timing and, more important, the magnitude of the resulting eruption."

The research appeared in Icarus , the journal of solar system studies.