Samstag, 20. September 2008

Ice wedges and climate change

The computer models used in climate change prediction lacks an important factor – the change in permafrost geographically extension and depth. Covering at least 22 to 38 millions square kilometres, mostly in circumarctic belt, it is thawing.
But still data about the mostly hidden ground ice is not complete, about his change and the impact of this change on the climate, for example trough the release of methane in the atmosphere.
Canadian researchers have published now an article in “Science” (Nr. 321, pag.1648) about an important find – impossible (or at least improbable) permafrost.
Duane Froese and colleagues of the University of Alberta have discovered ice wedges near the Dominion Creek in the Yukon, dated at least having 750.000 +- 60.000 years –the oldest ice of the nordamerican continent.

The ice is conservated in a depth of 3 to 4m under the modern landscape level, and was dated with ash-layers incorporated in the ice (Gold Run Tephra). This age implies that the ice has “survived” warm periods in the past, like the Eem-interglacial (126.000-115.000), considered so warm or even much warmer then the Holocene.
The researches do not dispute the fact that modern permafrost is thawing. Maybe the Canadian discontinuous permafrost reacts slower then previously though on climatic change, or the soil provides enough isolation to buffer warmer temperatures for longer periods.

Old ground ice is also known from permafrost in Siberia, but younger, with “only” 200.000 years.

Now only more discoveries of this kind can provide a clue if this are only local exceptions, or global warming is not consistent on the entire planet, or that there is the possibility that permafrost reactions to a warmer climate are more complex then we think and simulate.

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