THE discovery of the oldest ice in North America suggests that ice in permafrost regions can survive warmer periods than we thought.
Duane Froese of the University of Alberta in Edmonton, Canada, and colleagues dated a layer of ancient volcanic ash deposited above ice wedges within the permafrost of the Canadian Yukon. It proved the ice was 750,000 years old. This means it survived periods when the air temperature was up to 3 掳C higher than today (Science, vol 321, p 1648).
Many worry that if global warming melts such permafrost in the Arctic, it may release large volumes of greenhouse gases locked inside. But the newly found ice was a huge, deeply buried chunk, unlike the ice at shallow depths that may melt this century.
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