17 December 2011

Glacial chill ebbs and flows

This excellent article on some of the mechanics of climate change, most specifically the polar icecaps, is thought-provoking. The author alludes to both the medieval warm period and the little ice age. the latter one of the prime causal factors for the disappearance of the Norse settlements on Greenland. Take a look at my Axe of Iron novel series on the subject.


Glacial chill ebbs and flows

• by: Ian Plimer

• From: The Australian

• December 17, 2011 12:00AM

Ice conditions at the end of the Arctic melt season in 2007, captured by NASA's Advanced Microwave Scanning Radiometer and overlaid on the NASA Blue Marble. Source: AFP

ICE sheets grow and shrink. At times, they disappear. At other times, ice starts to cover polar areas and high mountains. That's what ice has done over the history of our planet. The Greenland and Antarctic basins are more than 1km deep, and deeper in the centres than around the edges, so that ice is squeezed uphill like toothpaste out of a tube by the weight of overlying ice. The alarmist media stresses that changing sea ice and continental glaciers indicate rapid global warming. Is this really so?

Since the last interglacial started some 10,500 years ago, summer sea ice in the Arctic has been far from constant. Sea ice comes and goes without leaving a clear record. For this reason, our knowledge about its variations and extent was limited before we had satellite surveillance or observations from aeroplanes and ships. A huge amount of the earth's surface water moves alternately between the ice sheets and the oceans.

Svend Funder, commenting on his recent Science paper, stated: "Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years. During the so-called Holocene Climate Optimum, from approximately 8000 to 5000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50 per cent of the summer 2007 coverage, which is absolutely the lowest on record.

"Our studies also show that when the ice disappears in one area, it may accumulate in another. We have discovered this by comparing our results with observations from northern Canada. While the amount of sea ice decreased in northern Greenland, it increased in Canada. This is probably due to changes in the prevailing wind systems. This factor has not been sufficiently taken into account when forecasting the imminent disappearance of sea ice in the Arctic Ocean."

In order to reach their unsurprising conclusions, Funder and the rest of the team organised several expeditions to Peary Land in northern Greenland. Funder said: "Our key to the mystery of the extent of sea ice during earlier epochs lies in the driftwood we found along the coast. One might think that it had floated across (the) sea, but such a journey takes several years, and driftwood would not be able to stay afloat for that long. The driftwood is from the outset embedded in sea ice and reaches the north Greenland coast along with it. The amount of driftwood therefore indicates how much multi-year sea ice there was in the ocean back then. And this is precisely the type of ice that is in danger of disappearing today."

What is interesting about this study is that the new understanding came from getting away from computer modelling and doing fieldwork in pretty inhospitable areas. Back in the laboratory and again away from computer models, the wood type was determined and dated using carbon-14. This wood came from near the great rivers of present-day North America and Siberia. This shows that wind and current directions have changed. The field study of coastal beach ridges shows that at times there were waves breaking unhindered by ice over at least 500km of coastline. At other times, due to sea ice cover, there were no beaches. This is the present situation.

Even if there is a great reduction in sea ice, all is not lost. Funder stated: "Our studies show that there are great natural variations in the amount of Arctic sea ice. The bad news is that there is a clear connection between temperature and the amount of sea ice. And there is no doubt that continued global warming will lead to a reduction in the amount of summer sea ice in the Arctic Ocean. The good news is that even with a reduction to less than 50 per cent of the current amount of sea ice, the ice will not reach a point of no return: a level where the ice no longer can regenerate itself even if the climate was to return to cooler temperatures.

"Finally, our studies show that the changes to a large degree are caused by the effect that temperature has on the prevailing wind systems. This has not been sufficiently taken into account when forecasting the imminent disappearance of the ice, as often portrayed in the media."

Those playing with computer climate models need to get outside, collect new data and take into account far more factors than they feed into computer models.

Studies of the behaviour of tropical glaciers over the last 11,000 years show irregular shrinkage, with slower rates in the Little Ice Age and faster rates in the 20th century. Glaciers such as the Bolivian Telata glacier reflect long-term warming during the current 10,500-year-long interglacial and that glacial retreat was in progress thousands of years before industrialisation.

Scientists urged on by the media state that ice calving off glaciers indicates global warming. Ice always falls off the front of a glacier. If ice did not melt, then the planet would now be covered in ice. Ice drops off the toe of both advancing and retreating glaciers and the melting snout of a glacier is at a point determined by the balance between the forward movement of the ice by gravity and the rate at which it melts. Ice falling off the front of a glacier means absolutely nothing when the air temperature is less than zero. Ice sheets grow and contract. At times, ice sheets disappear. The story of glacial retreat is far more complex than a television image.

Many glaciers that are now in retreat did not exist until the Little Ice Age (which climaxed in the middle to late 17th century). During the medieval warming (which peaked around AD1000), alpine glaciers in the northern hemisphere were smaller or did not exist. Over much of the Canadian Cordillera, there may have been no glaciers at all during the Holocene Maximum (8000 to 6500 years ago), when temperatures were considerably higher than now.

Records from New Zealand and Norway show glacier retreat started in the 18th and 19th centuries. Most of the modern ice retreat is due to post-Little Ice Age warming, changes in humidity and a decrease in ice flow rates.

The idea that a glacier slides downhill on a base lubricated by melt water was a good idea when first presented by Horace-Benedict de Saussure in 1779. We now know a lot more, yet this treasured idea remains. Ice moves by creep, a process of constant recrystallisation of ice crystals. Ice at the snout of a glacier has crystals 1000 times larger than those in snow as a result of growth during recrystallisation.

Ice sheets in Antarctica and Greenland first flow uphill before flowing down glaciers. The upward flow of ice cannot be due to human-induced global warming producing melting. There are some places in the world today where glaciers are expanding.

Ice sheets and glaciers grow and retreat for a great diversity of reasons. For scientists to argue that ice retreat is due to human activity is simplifying a very complex process. Furthermore, it is too cold in Antarctica and Greenland for ice to melt.

Since the discovery of the Hubbard Glacier (in Alaska) in 1895, it has been advancing 25m a year during periods of cooling and warming. The ice front is 10km long and 27m high. What does the ice do at the snout of the glacier? It falls off, because it is getting pushed from behind. This has nothing to do with temperature; it shows ice behaves as a plastic and brittle material and that ice sheets are always changing.

As with all areas of science, there are regular surprises. It was always thought that ice formed from frozen snow. The science was settled and there was a consensus. Recent work in East Antarctica shows that the deepest part of the ice sheet contains ice that did not originate as snow. It was melt water that seeped to the base of the ice sheet and then froze. The amount of ice formed by this method is probably greater in volume than all the glaciers on earth outside Antarctica and Greenland. The computer models predicted this melt-water escaped to the oceans and contributed to sea level rise. Wrong. The volume of water in this ice is larger than Antarctica's sub-glacial lakes. The addition of hundreds of metres of ice at the base of an ice sheet bends the overlying ice and causes uplift of the surface of the glacier. This changes the slope and flow of the ice. The thickest sub-glacial ice was 1100m and this pushed the top of glaciers up 410m to reflect the shape of the added basal ice.

Antarctica has another little surprise. Underneath the ice sheets are volcanoes. The last big eruption was in Roman times and Mount Erebus is continually restless. Addition of heat from below could cause massive melting and detachment of a large block of ice.

As snow falls, it traps air. This air is preserved as the snow becomes an ice sheet. This air remains trapped and uncontaminated in ice, otherwise it cannot be used to measure past atmospheres. Antarctic ice core (Siple) shows that there were 330 parts per million of carbon dioxide in the air in 1900; Mauna Loa Hawaiian measurements in 1960 show that the air then had 260ppm carbon dioxide.

Either the ice core data is wrong, the Hawaiian carbon dioxide measurements are wrong, or the atmospheric carbon dioxide content was decreasing during a period of industrialisation.

As in all other areas of science, uncertainty rules.

This is an extract from Ian Plimer's book How to Get Expelled from School: A Guide to Climate Change for Pupils, Parents & Punters.

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