Australia: The Land Where Time Began
Global warming to global freezing
According to climatologist William H Calvin, global climate switches from colder to warmer and vice versa every few thousand years (White, 2000). The suggestion is that global warming could lead to glacial conditions in as little as a decade. As global temperatures rise they will eventually reach a point at which there is enough freshwater entering the ocean from the glaciers on Greenland and other northern countries to shut down the global salt conveyor, the current powered by the increasing salt concentration of ocean water that result from ice formation in the northern winter. If this happens for more than a few consecutive winters major currents such as the Gulf Stream, and its extension, the North Atlantic Current, that is warmed by warm currents flowing north from the tropics that merges with the Gulf Stream, the now warmer water travelling eastward to Europe, and the eastward-blowing wind is warmed by this current, would stop flowing. These currents bring warmer water to the north of Europe that means they are 5-10o C warmer than the equivalent latitudes in North America and Asia. Should this occur, it could be expected that most food-producing areas of Europe would no longer be able to grow food, a more catastrophic event, with a much more rapid onset, than the much more slowing increasing effects of rising temperatures. The most heavily populated parts of the USA and Canada lie between 30o and 45o deg N latitude. The west to east wind, and the North Atlantic Current that warms it, bring enough warmth with them to allow food production 15o further north, up to 60o N at the tip of Greenland, that feeds a population more than double that of the US and Canada.
This warming current partially failed in the Little Ice Age. If it stopped completely, it would have a severe impact in Europe, and also the rest of the world. It has been estimated that the temperature at the equatorial regions would drop by about 5o C, this is estimated to drop the production of methane from tropical swamps, a cooling effect because methane is a greenhouse gas. Places like the Gobi Desert would put more dust into the air, also with a cooling effect. Based on geological history, Australia could be expected to become drier and windier.
If the salt conveyor current (thermohaline circulation) (great ocean conveyor) stopped flowing because ice didn't form in winter at the sites in the north Atlantic where it does at present the knock on effects would be felt globally.
There is some evidence that the thermohaline circulation may be slowing. Diminished wind chill, more floating ice, and more rain in the northern seas.
Diminished wind chill
This happens in places like the Labrador Sea at times when the North Atlantic Oscillation (an atmospheric circulation pattern similar to the El Nino of the Pacific) occurs. This atmospheric circulation pattern often lasts for a decade, from the Azores to Greenland. Weaker winds cause less salinity sinking in the Labrador Sea, Europe has colder winters. The atmosphere entered such a North Atlantic Oscillation Phase in 1996. And the Northern Hemisphere had colder winters.
Increased area of floating ice
The insulation of the sea surface from the atmosphere reduces the amount of evaporation from the ocean. The result is that more heat is retained in the water that then melts the ice. This cycle repeats about every 5 years.
Increased rainfall entering the northern seas
Fresh water in the ocean dilutes salt flushing (the sinking of water with high salt content). This is one of the effects predicted to result from global warming. The same effect could result from the moving of ice from the Arctic Ocean, as well as meltwater from the glaciers on Greenland. It is known that fjords on the east coast of Greenland have sometimes been dammed by glaciers that have collapsed. When these dams break they release Huge quantities of freshwater in a single mass. These large masses of freshwater usually remain mostly intact, not mixing significantly with the surrounding salty water. Just such an event is believed to be the origin of Great Salinity Anomaly, a mass of freshwater in the North Atlantic with a volume of 500 cubic miles. Such salinity anomalies move around the ocean and can disrupt currents, and ones of such huge dimensions can disrupt major currents.
Greenland ice cores have demonstrated that even within interglacials there is evidence that the climate can switch from a warm to a cool phase in 1or 2 decades. The Little Ice Age, from the early Renaissance to the end of the 19th century is an example. 2 other examples are the Younger Dryas from 12,700 to 11,400 BP, and one at 8200 BP that lasted for 100 years. The climate has been unusually stable for the last 8,000 years.
After the last glacial maximum the warming began abruptly 15,000 years ago, even though ice was still present, and Antarctica is still in the ice age. The Earth's orbit around the Sun has been connected to the 100,000 year cycle of glacial phases during the Pleistocene ice age over the last 2.6 million years.
Several of the links below report observations from the Arctic and Antarctic of events that could threaten the continued operation of the ocean conveyor.
Biomixing of the oceans
50 years ago, Charles Darwin, the grandson of the Charles Darwin of Origin of Species fame, discovered a mixing effect of marine creatures, the 'Darwin effect". Recent studies are finding that the combined effects of such vast numbers of marine animals, from krill to whales, play a major role in the mixing of the oceans. The fisheries of the world, as well as whalers, potentially have been changing the oceans, and ultimately the global climate, in ways that were not previously suspected. The vast numbers of jellyfish appearing in many places as the chemistry of the oceans change would be changing things still further. Animals that migrate between the surface and the depths on a daily basis, including plankton and jellyfish, may potentially have a disruptive effect on the ocean currents that presently redistribute heat around the oceans, thereby affecting the climate. See 14 and 15 below.
Increased volcanic activity
The history of Iceland's volcanoes suggests that volcanoes that are buried beneath glaciers can wake from dormancy when the covering glaciers are thinned. In the past, Icelandic volcanoes have undergone active periods when the glaciers covering them have thinned, resulting in lower pressure that allows more rock to become molten until the pressure is great enough to blast through any remaining covering. There are a number of volcanoes beneath glaciers, in particular a very large one in Antarctica that is covered by the 3 km of ice of the West Antarctic Ice Sheet, the same sheet that has been found to have collapsed without warning in the past, and has been described as Antarctica's most rapidly changing ice sheet. It last erupted in 325 BC, a bit over 2000 years ago.
Increased snowfall on Antarctica
It has been claimed that the Antarctic ice is not melting because the snowfall over Antarctica is increasing. This is only half the story, according to observations of scientists studying the Antarctic ice. The water temperature around Antarctica has increased more than the water temperatures in lower latitudes. As always occurs in other parts of the world, warmer water leads to higher rates of evaporation. In the Antarctic region this extra moisture in the air falls as snow, much of it over the central areas of the continent. They have found that the ice sheets are indeed growing by the addition of snow in their central regions, but simultaneously they are melting around their edges. Whether the ice sheets increase or decrease depends on which way the balance swings, is the snowfall the dominant factor, or is it the ice melting at the edges of the sheet the dominant factor? It is believed that the dominant factor is the loss of ice from the edges.
The situation is complicated by another observation. The same increased water temperature that increased the amount of snowfall is melting some the ice shelves from below. It has been found that while some are formed by the freezing of the sea water (the salt being added to the unfrozen water to increase the salinity locally), a number of these ice shelves are extensions of continental glaciers, the shelf being the part that extends out over the sea. With this type of ice shelf back pressure from the enormous amount of ice in the shelf, they can be up to 600 m thick and cover very large areas, greatly slows the flow of the associated glacier. As the ice shelves thin and disintegrate, as has occurred with the Larsen B Ice Shelf, among others, the associated glaciers flow to the sea accelerates. In the case of the Larsen B Ice Shelf that disintegrated in 2002, the associated glaciers were seen to increase their flow rate to about 8 times the rate while there was still backpressure from the ice shelf. Even though ice shelves can be up to 600 m thick, when they disintegrate and melt they don't raise the sea level by much (the 9/10ths below the surface characteristic of icebergs), when the ice from the glacier enters the sea it does raise the sea level. It is this (24). The same is happening with the Greenland ice sheets.
Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|