RE: Global Warming Nonsense.This is a neat bullet point summary of issues arising from Gobal warming, again anybody want diagrams inbox me an email address, or Join NewScientist.com
Appreciate this is partially off topic. Related only BB only in so far that action on global warming is likely to increase use of Hybrids and battery technology and hence Cobalt.
Idle
Climate change: Awaking the sleeping giants
* 12 February 2005
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Ice shelf collapse
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Ice shelf collapse
The soil problem
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The soil problem
The ocean conveyor belt
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The ocean conveyor belt
Greenland ice cap melts
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Greenland ice cap melts
Ocean becomes more acid
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Ocean becomes more acid
Deep-sea danger
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Deep-sea danger
West Antarctic ice sheet on the slide
WHILE the east Antarctic ice sheet sits on land, the west Antarctic ice sheet rests mostly on a part of the continental shelf that is below sea level. This may mean that the ice sheet is particularly prone to collapse, John Mercer of Ohio State University predicted in 1978. If the entire ice sheet slides off the continental shelf, iceberg by iceberg, global sea levels would rise by 5 metres regardless of whether the ice melts or not.
It appears the sheet is now slipping into the sea faster than it is being built up by snow. "The irreversible retreat of the west Antarctic ice sheet has already begun in the Pine Island Bay sector and will proceed to completion in 200 years." So warned Terry Hughes, a glaciologist at the University of Maine in 1983. Other glaciologists and more recently the Intergovernmental Panel on Climate Change have dismissed the idea that the collapse is under way and could happen on such a short timescale. But at the Exeter meeting, Chris Rapley, director of the British Antarctic Survey, warned of ominous signs of change. "We could be seeing the start of a runaway collapse of the ice sheet," he said. "This is a real cause for concern. We need to marshal world resources to find out what is going on."
Evidence: Three of the continent's biggest glaciers, around Pine Island in west Antarctica, are disappearing fast. They are losing an estimated 250 cubic kilometres a year. It may be a natural oscillation. But Rapley says the simultaneous melting suggests otherwise. Together, the three glaciers drain a third of the ice sheet.
How likely? Unclear.
When? Could already be under way.
Has it happened before? Yes. The last time may have been 100,000 years ago.
Impacts: Would raise sea levels by 5 metres within a few hundred years and, Hughes says, could destabilise the east Antarctic ice sheet, which contains enough ice to raise sea levels by 50 metres.
Reversible? Not this side of an ice age.
Soils give up their carbon stores
AT the moment, soils and forests absorb about a quarter of the carbon dioxide from the fossil fuels we pour into the air. The amount is increasing because plants are growing faster, fertilised by higher CO2 levels.
The natural system, says Peter Cox of the Centre for Ecology and Hydrology at Winfrith, UK, is helping to save us from ourselves. But it won't last. As temperatures rise, the rate at which wood, leaves, roots and organic material in the soil decompose and release CO2 is also speeding up. At some point, the rate of release will overtake the rate of absorption, and the land biosphere will switch from being a sink of CO2 to a large source. Once this threshold has been passed, stabilising CO2 levels will require much greater cuts in emissions (see Graphic).
Some models suggest the threshold will be reached when the level of CO2 in the atmosphere is between 400 and 500 parts per million. "I'd say this is one definition of what dangerous climate change means," Cox says.
Evidence: The underlying processes are not contentious, and are backed by small field and greenhouse experiments.
How likely? Very.
When? Within 10 to 50 years.
Has it happened before? Probably, millions of years ago.
Impacts: Rapid acceleration of global warming.
Reversible? Yes. Eventually sources and sinks would probably come back into balance, but only after large releases to the atmosphere.
Ocean conveyor belt shuts down
THE thermohaline circulation or ocean "conveyor belt" moves vast amounts of heat from the tropics towards the poles. Its best-known feature is the Gulf Stream, which keeps western Europe warm.
The conveyor is driven by the formation of ice in the North Atlantic, which leaves behind dense, salty water that sinks to the ocean floor. But this driver could be shut down if the ocean becomes too warm for ice to form or if the dense salty water is diluted by large amounts of fresh water from a melting Greenland ice cap.
The ocean circulation seems to have two distinct modes, depending on whether the thermohaline circulation is on or off. It could shut down in a matter of days, Hughes says. While many oceanographers say a switch-off is unlikely this century, a few researchers presented results in Exeter suggesting this may be unduly optimistic. Michael Schlesinger of the University of Illinois at Urbana-Champaign warns that if the melting Greenland ice cap is factored in, the circulation would "most probably shut down" after a 2 to 2.5 °C rise in temperatures. Another study puts the chance at 1 in 3 after a 3 °C rise.
Evidence: The North Atlantic has become less salty in recent years, perhaps due to Greenland's Zacharia ice stream and a sharp rise in river flows into the Arctic since 1965.
How likely? Uncertain, but recent studies are worrying.
When? Within the next 200 years.
Has it happened before? Yes, most recently 12,000 years ago.
Impacts: Europe would cool rapidly, more than negating the effects of global warming, while other areas such as Alaska would warm even faster. The Asian monsoon might fail.
Reversible? Not by reverting to conditions just before the switch.
Greenland's ice cap melts
MELTING of the 2-kilometre-thick Greenland ice cap would raise global sea levels by 7 metres. Once the ice cap starts to melt faster than ice accumulates from snowfall, the melting will accelerate. That is because the lower the altitude of the surface of the ice cap, the warmer the air above it will be. The consensus of model studies is that this "tipping point" will occur when there has been around 2.7 °C of warming.
Melting would probably take between 1000 and 3000 years to complete. But once it is under way, even a fall in global temperatures would not halt it, according to modellers at the UK's Hadley Centre. And in the shorter term, the rush of fresh meltwater into the North Atlantic could help halt the ocean conveyor belt.
Evidence: A massive river of ice 700 kilometres long, known as the Zacharia ice stream, is flowing out of north-eastern Greenland, but it is unclear if the flow is increasing.
How likely? Probable.
When? Could be under way later this century.
Has it happened before? Yes.
Impacts: The sea would inundate many of today's major population centres.
Reversible? Not this side of an ice age.
Methane burps
Locked away in sediments in the deep ocean and in permafrost on land is an estimated 5000 billion tonnes of methane, formed over millions of years from the decay of organic matter. In the ocean sediments the methane exists in the form of a gas hydrate, whose stability depends on high pressure and low temperatures.
Melting of permafrost and penetration of ocean warming into the sediments could release some of this methane. As methane is a potent greenhouse gas, this would cause a major and potentially catastrophic acceleration of global warming. The question is how much might be released, and how quickly. Danny Harvey of the University of Toronto will predict later this month that likely releases in the near future will increase warming by only 10 to 25 per cent. But David Archer of the University of Chicago says that a 3 °C warming would release 85 per cent of the methane after a few thousand years.
Evidence: Seasonal fluxes of methane from Arctic sediments suggest a response to temperature changes. And studies at Blake Ridge off the US east coast suggest rapid releases are possible.
How likely? Probable.
When? Impossible to predict.
Has it happened before? Yes, methane releases may have helped end past ice ages. There may have been a massive release around 55 million years ago.
Impacts: Potentially catastrophic global warming. Enough, suggests Archer, to prevent another ice age for half a million years, whatever we do.
Reversible? No.
Oceans become more acid
More than a third of the CO2 put into the air by human activity has dissolved in the oceans to form carbonic acid.
On currents trends, if there are no cuts in emissions, the pH of the ocean will fall 0.4 units by 2100 and 0.77 by 2250, according to estimates by Carol Turley of the Plymouth Marine Laboratory in the UK. "While climate change has uncertainty, these geochemical changes are highly predictable," she says.
Acidification will damage a wide range of organisms, including coral and shellfish that fix calcium carbonate from the ocean. There could also be unexpected feedbacks affecting the climate, with changes to nitrification processes disrupting phytoplankton, marine ecosystems and the ocean carbon cycle.
Evidence in the field: Ocean pH has already fallen by 0.1 units to 8.1.
How likely? Certain.
When? It is already under way.
Has it happened before? Not for at least 30 million years.
Impacts: Turley predicts a loss of a third of the world's coral by 2085.
Reversible? Yes, if CO2 levels fall. But by the time this is achieved, some species will be extinct, leaving affected ecosystems irreversibly changed.
Regional impacts
In addition to global changes, there could be a number of regional "sleeping giants" that could wake to have enormous impacts on certain parts of the globe. These include:
Death of the Amazon
Some climate models predict a big decline in rainfall that would leave it to dry out and burn sometime after 2050, adding to global CO2 emissions from the land biosphere.
The "greening" of the Sahara
It is not all bad. The Sahara seems to flip between desert and green partly because vegetation, once established, will generate enough extra rain to sustain itself. The Sahara was last "green" 6000 years ago, and global warming might make it green again. But even here there is a downside: dust from Sahara storms helps fertilise the Amazon, and its loss could add to the stress on drying rainforests.
Bigger ozone holes
Greenhouse gases trap heat in the lower atmosphere, leaving the stratosphere above cooler. This increases the risk of ozone holes forming over the Arctic and, perhaps, extending far enough south to affect heavily populated parts of Europe each spring.
Monsoon disrupted
The Asian monsoon, on which half of the world's population depends, could be affected in several ways. Warming alone is expected to increase its intensity, but a collapse of the ocean conveyor would, on past evidence, diminish the monsoon. Warming will also melt Himalayan glaciers, making the river flows on which many people depend less predictable.
From issue 2486 of New Scientist magazine, 12 February 2005, page 9