The world's longest cores have been drilled in the oldest ice sheets of Greenland and Antarctica, but ice from glaciers on tropical mountain summits also contains important information.

Ancient ice frozen for millennia in high altitudes in the tropics can provide a window to historical climate change says researcher Lonnie Thompson, who drills into tropical ice sheets in a search for clues about prehistoric weather. Thompson has pioneered the study of tropical ice cores, which he says are an important complement to polar cores (ice from near the North and South poles). Meet Thompson and take a tour of his freezer, where he stores ice cores from 45 expeditions in 18 countries. Thompson says clues in the ice suggest vast temperature changes over a short period of time.

	Tropical Ice Cores Ice samples are taken from snow-capped mountains in the tropics. See the lab where one team studies tropical ice cores. Lonnie Thompson A leading scientist in tropical ice core research explains the findings of his work.