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Retrospections Earth on the Rocks
 
Earth on the Rocks
Based on a blog entries for The Hot Zone
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Climate
Posted:   06/01/10
Author:    Alison Hawkes

Summary: There is a lot we don't yet understand about climate change, but humankind's influence on the Earth is becoming more and more apparent. Studying our effect will help us understand life's future on Earth.

Rebound

Sea Ice off Greenland's Coast
Greenland’s coastal areas, rebounding like a sponge as the ice melts away, is rising upward about an inch a year.

Geophysicists at the University of Miami found that if the trend continues, the acceleration could be as much as two inches per year by 2025.

“It’s been known for several years that climate change is contributing to the melting of Greenland’s ice sheet,” said Tim Dixon, a co-author of a study published in the latest Nature Geoscience.

“What’s surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response,” he said. “Even more surprising, the rise seems to be accelerating, implying that melting is accelerating.”

Apparently, the same uplift of rocky surfaces is happening on the islands of Iceland and Svalbard. The research fits expectations of what happens when the pressure caused by heavy ice eases.

Arctic Sea Ice. Credit: NASA
The researchers used GPS receivers stationed on Greenland’s rocky shores to come up with measurements of the position, vertical velocity, and acceleration for each site from 1995 onward.The rebound seems to have started in the 1990s and is a signal that Greenland could become the largest contributor to global sea level rise, according to the researchers.

They now want to go back to other GPS stations in areas where ice loss is believed to be the highest.

Ice Ice Baby

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.

Sea Ice minimum, 1979. Credit: 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.

Sea Ice minimum, 2005. Credit: NASA
“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).

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


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