An ice core from Antarctica showing a thick layer of volcanic ash (grey). Oregon State University

The Earth’s ice caps, in Greenland and Antarctica, are an invaluable record of climate over the past hundreds of thousands years. As each annual layer of snow falls, gets buried and eventually becomes glacial ice, it traps with it particles and gases from the time it fell. We use that record to examine how the atmosphere has changed.

This turns out to be one of the most important pieces of e