Can polar ice persist in hot times? Perhaps, under some conditions.
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Posted on 01/10/2008 6:13:59 PM PST by neverdem
Can polar ice persist in hot times? Perhaps, under some conditions.
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A large ice cap seems to have formed in Antarctica around 91 million years ago, during a period of extreme greenhouse warming.
The Turonian, a subsection of the Cretaceous that lasted from 93.5 million to 89.3 million years ago, was one of the warmest periods since life began. Tropical sea-surface temperatures were about 34-37 ºC — more than 5 ºC warmer than today. Even the waters surrounding Antarctica were about 20 ºC, warm enough for crocodiles to live where penguins swim today.
It was assumed that this world, where the atmosphere was thought to contain 3-10 times the level of greenhouse gases it does today, wouldn't have had large glaciers at the poles. But this seems to be wrong, researchers report in Science 1.
“It’s stimulating and informative to think about what sorts of climatic conditions generally allow the formation of polar ice caps,” says Michael Oppenheimer, a geoscientist at Princeton University in New Jersey. “But one should be very cautious about forming analogues between the Earth’s deep history and modern times.” There's too little in terms of firm facts or details about this ancient event to extrapolate to the climate today, he says.
Chemical shift
An international team, led by geologist André Bornemann of the University of Leipzig in Germany, looked at sediments from the bed of the tropical Atlantic. They found that 91.2 million years ago, seawater changed to contain a greater proportion of a heavier form of oxygen. The best explanation, they say, is that lighter isotopes preferentially evaporated, and were later locked up in ice after falling as snow at the pole.
This conclusion is consistent with other data suggesting that sea levels dropped by up to 40 metres at roughly the same time. A build-up of polar ice is one possible explanation.
The team suggests that large glaciers covered parts of Antarctica, which was then at its present polar position, for about 200,000 years. The glaciers were probably about half the size of the present Antarctic ice cap, and, unlike today, didn't reach the sea.
What's most puzzling to researchers is how glacier growth was triggered during a period of intense global warming. One possible explanation, says Bornemann, is that an intensified water cycle in the greenhouse climate led to increased snowfall over Antarctica's mountains and high plateaus.
But researchers think that this hydrological activity lasted longer than the 200,000-year duration of the ice cap. So some other shorter-lived phenomenon must have also been at work. Perhaps a known 400,000-year cycle in the eccentricity of the Earth’s orbit around the Sun also helped to cool the poles, the team speculates.
Future ice
The work should add to researchers' understanding of how ice caps form, persist, and melt away.
Most models of the current climate suggest that that the bulk of Antarctica’s ice, which lies to the east of a mountain range running across the continent, won't collapse even in the face of quite substantial warming. But the ice to the west of the mountains isn't so secure.
"What we are really concerned about is the fate of the smaller and much more vulnerable west-Antarctic and Greenland ice sheets, which some believe could entirely disappear by the end of this century," says Oppenheimer.
The data from this paper isn't precise enough to help determine if and when that ice will melt. "We could rapidly lose all of Greenland’s and western Antarctica’s ice, and it would still not be inconsistent with this paper," Oppenheimer says.
They didn’t get the memo.
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Milankovitch Orbital Theory of global climate strikes again!
Plus, data suggests that there is ice at one pole on Mercury! (No, not Mercury Nevada).
Actually, it looks like they did get it...
~~Anthropogenic Global Warming ™ ping~~
Bushes fault! He must have gone back in time in Roves time machine and done it!
Hey, someone finally read those 30-year-old text books on oceanic atmospheric interactions. Glaciers form at altitude on mountain from warm moist air. Most of our glaciers are shrinking now because we are too cold. They are melting at the bottom end while their top ends are not being fed with fresh snow. We need to reverse this global warming argument and ask why we are being denied the benefits of a warmer world. The Roman Empire flourished when it was a degree and half warmer. We are still shy by a half a degree of the weather that forth the renaissance.
Global warming doesn’t explain why the artic ice is refreezing earlier and faster than ever before after one of the larger melting seasons this century.
Of course, global warming cannot predict virtually anything that its adherents would be willing to bet on.
Thanks for the link.
They are making it up as they go along, hoping to plug holes that keep appearing in their current “global warming” / “climate change” theory.
YEC INTREP
What the global warming freaks never understand about the POLES, is that they are in 6 months of darkness every year. The arctic sea ice is going to reform as soon as the sun goes below the horizon on September 21st EVERY year.
There has always been ice at the poles in the history of the planet (at least in the winter).
There has always been glaciers at the poles whenever there was a landmass at the poles.
Oceans might have sea ice in the winter and melt in the summer, but if there is land over the pole, there has always been glaciers there (see 6 months of darkness followed by 6 months of sunlight at 23 degrees above the horizon ie. no power.)
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