TIME CAPSULES
Until you see one, the idea of an iceberg can seem quite academic. Seen for the first time it will look astonishingly white. This whiteness comes from the bubbles of air trapped in the ice and will tend more towards blue if the ice has been compressed in its formation.
These bubbles are fascinating to climate scientists as they are perfect samples of the atmosphere from times past. The Antarctic ice sheet, where these icebergs are formed, is up to 4km thick in places and this can provide examples of atmosphere back a good 200,000 years or so.
That is far enough back to record major climate events and the ill-conceived sins of civilization. Volcanic eruptions, nuclear tests and the rise of the coal-fired steam engine are
