- Posts: 10120
- Joined: Wed Jul 01, 2009 9:10 pm
- Location: Packing my stuff and moving to Denver like you should be doing
ScienceDaily (Sep. 25, 2009) — The most comprehensive picture of the rapidly thinning glaciers along the coastline of both the Antarctic and Greenland ice sheets has been created using satellite lasers. The findings are an important step forward in the quest to make more accurate predictions for future sea level rise.
Reporting this week in the journal Nature, researchers from British Antarctic Survey and the University of Bristol describe how analysis of millions of NASA satellite measurements* from both of these vast ice sheets shows that the most profound ice loss is a result of glaciers speeding up where they flow into the sea.
The authors conclude that this 'dynamic thinning' of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic coastlines, is penetrating far into the ice sheets' interior and is spreading as ice shelves thin by ocean-driven melt. Ice shelf collapse has triggered particularly strong thinning that has endured for decades.
Lead author Dr Hamish Pritchard from British Antarctic Survey (BAS) says, "We were surprised to see such a strong pattern of thinning glaciers across such large areas of coastline – it's widespread and in some cases thinning extends hundreds of kilometres inland. We think that warm ocean currents reaching the coast and melting the glacier front is the most likely cause of faster glacier flow. This kind of ice loss is so poorly understood that it remains the most unpredictable part of future sea level rise."
The scientists compared the rates of change in elevation of both fast-flowing and slow-flowing ice. In Greenland for example they studied 111 fast-moving glaciers and found 81 thinning at rates twice that of slow-flowing ice at the same altitude.They found that ice loss from many glaciers in both Antarctica and Greenland is greater than the rate of snowfall further inland.
In Antarctica some of the fastest thinning glaciers are in West Antarctica (Amundsen Sea Embayment) where Pine Island Glacier and neighbouring Smith and Thwaites Glacier are thinning by up to 9 metres per year.
FAIR USE NOTICE.
Section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, . http://www.law.cornell.edu/uscode/17/107.shtml
The Snowball Earth hypothesis as it was originally proposed suggests that the Earth was entirely covered by ice during parts of the Cryogenian period, from 790 to 630 million years ago. It was developed to explain sedimentary deposits generally regarded as of glacial origin at seemingly tropical latitudes, and other enigmatic features of the Cryogenian geological record. The existence of a Snowball Earth remains controversial, and is contested by various scientists who dispute the geophysical feasibility of a completely frozen ocean, or the geological evidence on which the hypothesis is based. The initiation of a Snowball Earth event would involve some initial cooling mechanism, followed by runaway cooling due to increasing ice accumulation. The initial cooling could be facilitated by an equatorial continental distribution, which would increase the Earth's albedo near the equator, where most solar radiation is incident.
This arrangement would also allow rapid, unchecked weathering of continental rocks, a process that absorbs the greenhouse gas carbon dioxide from the atmosphere, resulting in further cooling. Alternatively, changes in solar energy output or perturbations of Earth's orbit could act as a trigger. However the initial cooling comes about, resultant ice accumulation would reflect solar energy back to space, further cooling the atmosphere and generating more ice cover. This feedback loop could eventually produce a frozen equator as cold as modern-day Antarctica. To break out of this icy condition either the level of solar energy incident on Earth would have to increase significantly, or huge quantities of greenhouse gases, emitted primarily by volcanic activity, would have to accumulate over millions of years. The eventual melting would perhaps take as little as 1,000 years.
One computer simulation of conditions during the Snowball Earth period.
There is a controversial theory that for millions of years the Earth was entirely smothered in ice, up to one kilometre thick. The temperature hovers around -40ºC everywhere, even in the tropics and the equator. If it did, then virtually nothing could survive this ferocious climate. There are some tantalising geological clues that show this theory may be true but the problem is, the clues and the Snowball Earth theory defy the laws of nature. For over fifty years a group of scientists has been trying to prove this incredible period of Earth history. Struggling against scepticism and disbelief, now finally the many mysteries have been solved and the scientific community is slowly coming around to the extraordinary idea not just of the dramatic freeze, but of an equally dramatic thaw. Scientists across the world are starting to believe that in the past the Earth froze over completely for ten million years... then warmed up rapidly about 600 million years ago. Almost all life was wiped out. But out of the freeze emerged the first complex creatures on Earth. Scientists now believe that the so-called Snowball Earth theory could hold the key to the evolution of complex life on this planet.
The discovery of this theory is a classic scientific detective story. For decades there had been a growing 'X-File' of geological anomalies haunting the scientific community. Telltale signs of past glaciation have been found in places that should have been much too hot - very near the equator. Even during the most severe ice age, scientists believed that the ice only reached as far down as Northern Europe and the middle of the USA. So what could these tropical deposits mean? Back in the 1960s one of the first climate modellers, Mikhail Budyko, stumbled on an ingenious answer. Through some simple mathematical formulae, he calculated that if the polar ice caps had spread past a crucial point, a runaway freezing process would have followed, eventually freezing over the whole of the planet. The idea fascinated scientists, but no one thought his runaway glaciation was anything more than a theoretical result. Surely it had never actually happened on planet Earth?
The idea foundered because according to the model, once the Earth was frozen there was no way out - the Earth would remain frozen forever. The big freeze would wipe out all life; we would not exist today. It seemed patently absurd. But then came a series of insights and inspirations from a geologist in California, Joe Kirschvink, who came up with a brilliant solution - that volcanoes, protruding above the frozen landscape, would have carried on pumping out carbon dioxide, the greenhouse gas, even though the world had entered the deep freeze. On Snowball Earth there was no rain to wash this carbon dioxide out of the atmosphere. Instead it would have built up to higher and higher concentrations - until eventually it sparked off not just global warming but global meltdown.
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials
From the baking landscape of Africa to ice-covered Antarctica, Horizon follows the tale of a theory which, if true, would have huge implications. Because scientists now believe this cycle of freezing and frying may have created the unique conditions needed for the evolution of complex life, including our own. Survival of life through frozen periods: A tremendous glaciation would curtail plant life on Earth, thus letting the atmospheric oxygen be drastically depleted and perhaps even disappear, and thus allow non-oxidized iron-rich rocks to form.
However, organisms and ecosystems, as far as it can be determined by the fossil record, do not appear to have undergone the significant change that would be expected by a mass extinction. Even if life were to cling on in all the ecological refuges listed above, the post-Snowball biota would have a noticeably different diversity and composition. This change in diversity and composition has not yet been observed. In fact, the organisms which ought to be most susceptible to climatic variation emerge unscathed from the Snowball Earth.
= Since Dawn Of Time The Fate Of Man Is That Of Lice =
- Related topics
- Last post