The conclusions cited here appear to conflict with other available proxies that are themselves interpretive. I likely need access to the data itself so that it may be compared and perhaps correlated. The conclusions are a bit to glib and discovering the weaknesses of other data sets makes one skeptical and cautious.
I have one hundred thousand year cycles in the ice cores or perhaps they are forty thousand year cycles. It does not seem likely, does it?
I suspect that uniform cycles were observed and they convinced themselves that the proper time component was forty thousand years. I am beginning to think that trusting any age assignment is reckless.
I also observe the crustal shift conjecture would have made the western ice sheet specifically more vulnerable to a full melt and that is not necessarily true today.
We will have to keep our eyes open for the papers and the data.
I hate to be a spoil sport, but a careful reading of the material strongly suggests that they have linked the data to the known Milankovitch cycle and have corelated their data accordingly. If in fact the data is actually reflecting the 100,000 Sirius orbit then the data has been distorted by a factor of 2.5.
More importantly, the Milankovitch cycle is a very unlikely contender as a causitive agent for full polar melting. The variation is not convincing enough. However, a passage through the high infrared environment of Sirius is very convincing. Space habitats are looking better all the time when the earth turns into an alligator swamp.
Antarctic drilling yields global warming insights
By William Mullen Tribune reporter
1:46 PM CDT, March 18, 2009
Scientists studying the geophysical mechanisms behind the periodic cycles of freezing and melting at the polar ends of the earth reported today that Earth is headed toward another thaw, though it might take a thousand years or more for it to happen.
The research comes from cores drilled out of the ocean floor in Antarctica in 2006. The drilling project, co-directed by a scientist from Northern Illinois University and known as ANDRILL, was one of the largest science projects ever undertaken on the continent.
In a report published on the cover of the research journal Nature, the researchers found that during the Pliocene epoch 3 to 5 million years ago--a time when conditions in Antarctica are similar to today's -- the ice in Antarctica collapsed and melted on a regular basis, raising world sea levels.
Polar ice began melting on a massive scale when atmospheric carbon dioxide levels were up to around 400 parts per million in the Pliocene, said Northern Illinois University geologist Ross Powell, one of the chief ANDRILL scientists. "Today and we are now at 386 parts per million and rising," he said, and it grows by one part per million every year, thanks to carbon dioxide that human activity is putting into the atmosphere.
Scientists are particularly concerned about the West Antarctic Ice Sheet, which has collapsed with great regularity about every 40,000 years and is currently in an unstable state. If all the ice atop West Antarctica today melted, it would raise world sea levels 16 feet, inundating major cities and coastal areas where billions of people live.Two climate modelers, David Pollard of Pennsylvania State University and Robert DeConto of the University of Massachusetts, say the ANDRILL data suggest it probably would take 1,000 or more years from the beginning of a warm-up until the ice sheet would melt away.
Over the Earth's geologic history, polar freeze/thaw cycles have occurred about every 40,000 years because of a natural shift in the tilt of the Earth's axis known as the Milankovitch Cycle.
"The tilting changes the amount of radiation absorbed into each hemisphere of the Earth, depending on which hemisphere is tilted closest to the sun," said Powell. That leads to a gradual build-up of atmospheric carbon dioxide, he said, and eventually destabilizes and melts the ice shelves and ice sheets in Antarctica.
But human activity appears to be having its own effect on the world's climate, by driving temperatures warmer than they otherwise would be, said geologist Reed Scherer, also a member of the ANDRILL team from Northern Illinois University.
"If something is an external cycle," Scherer said. "It should be predictable. But it is much more complicated than that, and we seem to be throwing the pattern off balance now. It used to be that carbon dioxide rises were driven by the cycle. Now atmospheric carbon dioxide is driving the system."
In the past, everything known about climate history came from geological data collected in the northern hemisphere and very little scientific data existed from Antarctica, which holds 70 percent of the world's fresh water as ice atop the continent.
The ANDRILL core, extracted by a rig constructed atop an ice shelf in west Antarctica's Ross Sea, is the first detailed geological data on Antarctic climate history, giving scientists and climate modelers a far more complete picture of world climate history.
Earth's average annual temperature has risen 1.4 degrees Fahrenheit in the last 100 years, but over west Antarctica it has risen 4.5 degrees.
DeConto said that the historical data provided by ANDRILL has been a great milestone in climate understanding but that the role of heating and cooling ocean temperatures is even more pertinent to the stability of both the Antarctic ice sheets and the ice shelves that surround the continent.
"The next big step," said DeConto, "is to determine what is happening to the ocean temperatures under the ice shelves and around the ice sheet. We really need that information."