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Arctic has survived 'astonishing' periods extreme warming before

Doug O'Harra
Courtesy Olaf Juschus, Eberswalde University for Sustainable Development

Imagine a much, much warmer climate enveloping Alaska and the Arctic.

Sea levels have risen, and sea ice hardly exists. Greenland’s ice cap has vanished. The Bering Strait flows strong and deep, sluicing warm Pacific water into the polar ocean all year long.

Forests of spruce and possibly pine grow close to the shores of the Chukchi and Beaufort seas. Tundra has all but disappeared. A rise in annual temperatures regularly bathes frigid Barrow with warmth comparable to that now found south of the Brooks Range, and chilly Kotzebue gets soothed and pampered with a soft regime that feels somewhat like Fairbanks and the Tanana Valley of today.

Yeah, yeah, you say. Is this yet another one of those tedious warnings about what will happen to us Northerners sometime in the future if we don’t turn down the thermostat and park our four-wheel-drive mud trucks?

Not at all. This is a startling glimpse into the polar climate of the not-so-distant past.

Deep drilling into the never-glaciated Siberian Lake El’gygytgyn has uncovered evidence of extreme Arctic warming occurring at irregular intervals during the past 2.8 million years, with at least two episodes where the Far North climate posted average annual temperatures up to 9 degrees Fahrenheit warmer than our modern hiatus from ice age conditions.

An international scientific team says that these “super-interglacials” — one about 400,000 years ago and one about 1.1 million years ago — cannot be explained by existing understanding of how ice ages wax and wane, according to a new study published in the journal Science.

“What we see is astonishing,” said Julie Brigham-Grette, the lead U.S. scientist in the project, in a recent story. “We had no idea that we’d find this. It’s astonishing to see so many intervals when the Arctic was really warm, enough so forests were growing where today we see tundra and permafrost. And the intensity of warming is completely unexpected.”

Arctic warming triggers

Changes in solar energy or shifts in greenhouse gas concentrations or any other known climate forcings do not create the same results in supercomputing climate models. But in what shows that the home planet’s climate system might be far more interactive and intricate than anyone has realized, the scientists found these episodes of Arctic summer were linked to the collapsing of the West Antarctic Ice Sheet, some 12,000 miles away at the bottom of the world in the opposite hemisphere.

“Analytical results from the longest sediment core that has ever been drilled in the terrestrial areas of the Arctic have shown temperatures that were previously considered impossible for the Arctic Circle,” the 17 co-authors reported in this story about the results, posted by the German research center that helped date the samples. “In addition, a notable correlation of the warm periods in the Arctic with large melting events in Antarctica points to previously unknown interactions between the Polar Regions.”

"The polar regions are much more vulnerable to change than we thought before," added the project's co-chief scientists Martin Melles of the University of Cologne, Germany, Brigham-Grette of the University of Massachusetts Amherst, and Pavel Minyuk of Russia's North-East Interdisciplinary Scientific Research Institute in Magadan, in another story released to media around the world.

"The exceptional climate warmings in the Arctic and the obvious inter-hemispheric interdependencies were not known before our studies,” they added. "The data are of global significance, taking strong indications for an ongoing collapse of ice shelves around the Antarctic Peninsula and margins of the West Antarctica Ice Sheet and its potential acceleration in the near future. In this respect, the past could be the key to the future.”

The results come from a team involving more than 50 scientists from four countries. The new Science report is the first of two overview papers, to be followed by another two dozen reports.

Ancient crater gives up its secrets

The focus, really, is on the product of an ancient interplanetary accident.

Lake El’igygytgyn formed some 3.6 million years ago, after a meteorite smashed into a remote patch of Siberia and created a crater about 11 miles wide. The locale — some 650 miles northwest of Nome and about 1,200 miles from Anchorage — was never glaciated during the many ice age maximums that overran much of the Far North ever since. That means the lake has been continuously accumulating gunk and other sediment without interruption — in effect storing an unbroken record of the regional climate over millions of years.

In contrast, ice cores taken from the Greenland ice cap reach back only about 110,000 years.

For the project, sponsored largely by the National Science Foundation, the team bored four holes into the lake sediments during the winter of 2008-09, in one instance recovering 900 feet from a 1,400-foot-long core reaching back in time nearly three million years. The samples underwent a battery of sophisticated tests for trace mineral ratios and biochemical signatures that would offer clues into air temperature when the material was deposited. They also looked at pollen to get a fix on what types of plants thrived before, during and after the extraordinary warm periods.

Much more detail about the project can be found posted by University of Cologne and U Mass.

In general, the scientists found evidence of a much warmer and wetter Arctic world, a place where forests spread another 600 miles farther north than they do now, all during an era when ice melted away and sea level soared.

“The sediment cores from Lake El'gygytgyn reflect the climatic and environmental history of the Arctic with great sensitivity,” the scientists explained in this NSF story:

To quantify the climate differences, the scientists studied four warm phases in detail: the two youngest, called "normal" interglacials, from 12,000 years and 125,000 years ago; and two older phases, called "super" interglacials, from 400,000 and 1.1 million years ago.

According to climate reconstructions based on pollen found in sediment cores, summer temperatures and annual precipitation during the super interglacials were about 4 to 5 degrees C warmer, and about 12 inches wetter, than during normal interglacials.

A disturbing Antarctic connection

In a search for causes, the scientists looked to sediment cores from Antarctica and discovered a remarkable correlation between these Arctic “super-interglacials” and the disintegration of the ice sheet off West Antarctica. More work needs to be done, but Melles said it’s possible the genesis for episodes of extreme warming in the Far North might lie in the Far South.

“Despite being half a world away, the collapse of the ice sheet might be the trigger for an Arctic super-interglacial, says Melles,” according to a good explainer published this week in New Scientist. “As the (West Antarctic Ice Sheet) disintegrates, it would raise global sea levels by about 5 metres. This would push more warm water from the Pacific Ocean through the Bering Strait into the Arctic Ocean, warming the Arctic region.”

“We have a lot more to learn,” Brigham-Grette said in this story. “But our results mesh with what glaciologists are seeing today. Seven of the 12 major ice shelves around the Antarctic are melting or are gone. We suspect the tipping point for the gradual de-glaciation of Greenland and the Arctic may be lower than glaciologists once thought.”