The Hot Zone

Ice, ice baby

Posted by Alison Hawkes on May 16, 2010
Category : Climates of the Past, The Oceans

Maybe the most defining characteristic of the Arctic is its ice. What would the Arctic be, if not for a frigid, barren, icy landscape?

We’ve come to lament the loss of sea ice in the Arctic. Yet it’s interesting to note that the Arctic has, in fact, been ice free and for long periods of time. As recently as 125,000 years ago, the summertime brought ice-free conditions. In fact, it probably wasn’t until 14 million years ago — the launch of a cooling period — that the Arctic sea ice achieved any kind of perennial presence.

Arctic Sea Ice, NASA

Arctic Sea Ice, NASA

Sea ice has varied by cycles of warm and cold, determined by Earth orbital patterns and other factors. Just 5,500 years ago — around the time of the first human writings — the Arctic ice became thick and “old,” the kind of ice we sent explorers into and that colored childhood visions of the North Pole.

Research into long term changes in Arctic sea ice conditions has been carried out by many scientists, who have looked at such cues as ice cores, remnants of coastal vegetation, marine sediments, skeletal remains of organisms, and even historical records from the shipping industry that dates back to 1870. Icelanders have been keeping records of drift ice since they settled the frigid island in 870 AD.

But pulling it all together was Ohio State University geologist Leonid Polyak and his colleagues in a comprehensive summary, History of Sea Ice in the Arctic, published in February in the journal Quaternary Science Reviews. The objective is clear. Polyak et. al. make a compelling case for modern day climate change.

“Arctic sea ice extent and volume are declining rapidly,” they write. “Several studies project that the Arctic Ocean may become seasonally-ice free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions throughout the geologic past.”

It’s not that the Arctic hasn’t experienced ice-free conditions in the past. The point they’re underscoring is the pace of change. Seasonal ice has been in retreat since about 1900 – the Industrial Revolution — and has greatly accelerated in pace in the last five decades. Old Arctic ice, defined as ice that has been in place for least five years, dropped by 56 percent from 1982 to 2007 (the lowest level of sea ice in satellite records).

Sea Ice minimum, 1979, NASA

Sea Ice minimum, 1979, NASA

Sea Ice minimum, 2005, NASA

Sea Ice minimum, 2005, NASA

With higher temperatures potentially reversing what has been a long-term cooling trend in Earth history, human behavior is essentially driving the change.

- Alison Hawkes

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