YOU would expect that any evidence of how ancient volcanoes influenced Earth鈥檚 climate went up in smoke long ago. Not so. It now seems that traces of past eruptions are locked up in the Antarctic ice, and can reveal if the plumes were massive enough to affect climate.
Volcanic particles that enter the stratosphere 鈥� the layer of Earth鈥檚 atmosphere from about 10 to 50 kilometres up 鈥� undergo a distinctive reaction in the presence of intense ultraviolet light, affecting the ratios of sulphur isotopes that are eventually carried down to Earth as sulphate compounds. M茅lanie Baroni of Joseph Fourier University in St-Martin-d鈥橦猫res, France, and her colleagues studied volcanic particles in ice core samples from Antarctica, a region not contaminated by human emissions.
They detected two past eruptions that punched through into the stratosphere: the Philippines鈥� Mount Pinatubo in 1991 and Indonesia鈥檚 Mount Agung in 1963. Both eruptions affected Earth鈥檚 climate by blocking out sunlight. Pinatubo is estimated to have cooled Earth by about 0.5 掳C.
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Now Baroni and her colleagues have drilled an ice core that dates back 1 million years, in order to find stratospheric eruptions. 鈥淚t is helping us to work out the climatic impact these eruptions have,鈥� she says.
